BOK Financial (BOKF) 10-K 27 Feb 18 2017 FY Annual report Financial data

Document And Entity Information

Document And Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2017	Jan. 31, 2018	Jun. 30, 2017
Document and Entity Information [Abstract]
Entity Registrant Name	BOK FINANCIAL CORP ET AL
Entity Central Index Key	875,357
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Entity Public Float			$ 2,096,658,923
Entity Common Stock, Shares Outstanding		65,550,406
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	FY
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2017

Consolidated Statements of Earn

Consolidated Statements of Earnings - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Interest and dividend revenue [Abstract]
Loans	$ 696,479	$ 581,030	$ 529,683
Residential mortgage loans held for sale	8,706	12,658	13,602
Trading securities	17,002	8,527	2,240
Investment securities	16,121	16,894	18,098
Available for sale securities	177,070	175,321	174,829
Fair value option securities	16,755	6,723	9,264
Restricted equity securities	18,490	17,238	13,532
Interest-bearing cash and cash equivalents	22,128	10,726	5,580
Total interest and dividend revenue	972,751	829,117	766,828
Interest expense [Abstract]
Deposits	53,803	40,494	44,170
Borrowed funds	69,124	35,336	14,204
Subordinated debentures	8,123	6,059	5,100
Total interest expense	131,050	81,889	63,474
Net interest and dividend revenue	841,701	747,228	703,354
Provision for credit losses	(7,000)	65,000	34,000
Net interest and dividend revenue after provision for credit losses	848,701	682,228	669,354
Other operating revenue [Abstract]
Brokerage and trading revenue	131,601	138,377	129,556
Transaction card revenue	119,988	116,452	109,579
Fiduciary and asset management revenue	162,893	135,477	126,153
Deposit service charges and fees	112,075	111,499	109,473
Mortgage banking revenue	104,719	133,914	126,002
Other revenue	52,168	51,029	49,883
Total fees and commissions	683,444	686,748	650,646
Other gains, net	9,004	4,030	5,702
Gain (loss) on derivatives, net	779	(15,685)	430
Loss on fair value option securities, net	(2,733)	(10,555)	(3,684)
Change in fair value of mortgage servicing rights	172	(2,193)	(4,853)
Gain on available for sale securities, net	4,428	11,675	12,058
Total other-than-temporary impairment losses	0	0	(2,443)
Portion of loss recognized in other comprehensive income	0	0	624
Net impairment losses recognized in earnings	0	0	(1,819)
Total other operating revenue	695,094	674,020	658,480
Other operating expense [Abstract]
Personnel	573,408	553,119	515,298
Business promotion	28,877	26,582	27,851
Charitable contributions to BOKF Foundation	2,000	2,000	796
Professional fees and services	51,067	56,783	40,123
Net occupancy and equipment	86,477	80,024	76,016
Insurance	19,653	32,489	20,375
Data processing and communications	146,970	131,841	122,383
Printing, postage and supplies	15,689	15,584	13,498
Net losses and operating expenses of repossessed assets	9,687	3,359	1,446
Amortization of intangible assets	6,779	6,862	4,359
Mortgage banking costs	52,856	61,387	38,813
Other expense	32,054	47,560	35,233
Total other operating expense	1,025,517	1,017,590	896,191
Net income before taxes	518,278	338,658	431,643
Federal and state income taxes	182,593	106,377	139,384
Net income	335,685	232,281	292,259
Net income (loss) attributable to Non-controlling interests	1,041	(387)	3,694
Net income attributable to BOK Financial Corporation shareholders	$ 334,644	$ 232,668	$ 288,565
Earnings per share: [Abstract]
Basic (in dollars per share)	$ 5.11	$ 3.53	$ 4.22
Diluted (in dollars per share)	$ 5.11	$ 3.53	$ 4.21
Average shares used in computation: [Abstract]
Basic (in shares)	64,745,364	65,085,627	67,594,689
Diluted (in shares)	64,806,284	65,143,898	67,691,658
Dividends declared per share (in dollars per share)	$ 1.77	$ 1.73	$ 1.69

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Comprehensive Income [Abstract]
Net income		$ 335,685	$ 232,281	$ 292,259
Other comprehensive income (loss), before income taxes: [Abstract]
Net change in unrealized gain (loss)		(26,152)	(41,521)	(46,803)
Reclassification adjustments included in earnings: [Abstract]
Interest revenue, Investment securities, Taxable securities		0	(112)	(503)
Interest expense, Subordinated debentures		0	0	121
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Period Increase (Decrease)		0	0	(1,819)
Gain on available for sale securities, net		(4,428)	(11,675)	(12,058)
Other comprehensive loss, before income taxes		(30,580)	(53,308)	(57,424)
Federal and state income taxes	[1]	(11,923)	(20,754)	(22,338)
Other comprehensive loss, net of income taxes		(18,657)	(32,554)	(35,086)
Comprehensive income		317,028	199,727	257,173
Comprehensive income (loss) attributable to non-controlling interests		1,041	(387)	3,694
Comprehensive income attributable to BOK Financial Corp. shareholders		$ 315,987	$ 200,114	$ 253,479
[1]	Calculated using 39% effective tax rate.

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Assets [Abstract]
Cash and due from banks	$ 602,510	$ 620,846
Interest-bearing cash and cash equivalents	1,714,544	1,916,651
Trading securities	462,676	337,628
Investment securities	461,793	546,145
Available for sale securities	8,321,578	8,676,829
Fair value option securities	755,054	77,046
Restricted equity securities	320,189	307,240
Residential mortgage loans held for sale	221,378	301,897
Loans	17,153,424	16,989,660
Allowance for loan losses	(230,682)	(246,159)
Loans, net of allowance	16,922,742	16,743,501
Premises and equipment, net	317,335	325,849
Receivables	442,897	772,952
Goodwill	447,430	448,899
Intangible assets, net	28,658	46,931
Mortgage servicing rights	252,867	247,073
Real estate and other repossessed assets, net of allowance	28,437	44,287
Derivative contracts	220,502	689,872
Cash surrender value of bank-owned life insurance	316,498	308,430
Receivable on unsettled available for sale securities sales	75,980	7,188
Other assets	359,092	353,017
Total assets	32,272,160	32,772,281
Deposits [Abstract]
Noninterest-bearing demand deposits	9,243,338	9,235,720
Interest-bearing Deposit Liabilities [Abstract]
Transaction	10,250,393	10,865,105
Savings	469,158	425,470
Time	2,098,416	2,221,800
Total deposits	22,061,305	22,748,095
Funds purchased	58,628	57,929
Repurchase agreements	516,335	668,661
Other borrowings	5,134,897	4,846,072
Subordinated debentures	144,677	144,640
Accrued interest, taxes and expense	164,895	146,704
Derivative contracts	171,963	664,531
Due on unsettled available for sale securities purchases	151,198	6,508
Other liabilities	349,928	182,784
Total liabilities	28,753,826	29,465,924
Shareholders' equity: [Abstract]
Common stock	4	4
Capital surplus	1,035,895	1,006,535
Retained earnings	3,048,487	2,823,334
Treasury stock	(552,845)	(544,052)
Accumulated other comprehensive loss	(36,174)	(10,967)
Total shareholders’ equity	3,495,367	3,274,854
Non-controlling interests	22,967	31,503
Total equity	3,518,334	3,306,357
Total liabilities and equity	$ 32,272,160	$ 32,772,281

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Investment securities [Abstract]
Investment securities, fair value	$ 480,035	$ 565,493
Real estate and other repossessed assets, allowance	$ 12,648	$ 9,562
Shareholders' equity: [Abstract]
Common stock, par value (in dollars per share)	$ 0.00006	$ 0.00006
Common stock, authorized (in shares)	2,500,000,000	2,500,000,000
Common stock, shares issued (in shares)	75,147,686	74,993,407
Common stock, shares outstanding (in shares)	75,147,686	74,993,407
Treasury stock, shares at cost (in shares)	9,752,749	9,655,975

Consolidated Statements of Chan

Consolidated Statements of Changes in Equity - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock [Member]	Capital Surplus [Member]	Retained Earnings [Member]	Treasury Stock [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Total Shareholders' Equity [Member]	Non-Controlling Interests [Member]
Balance, beginning of period (in shares) at Dec. 31, 2014		74,004			4,890
Balance, beginning of period at Dec. 31, 2014	$ 3,336,206	$ 4	$ 954,644	$ 2,530,837	$ (239,979)	$ 56,673	$ 3,302,179	$ 34,027
Net income	292,259			288,565			288,565	3,694
Other comprehensive loss	(35,086)					(35,086)	(35,086)
Repurchase of common stock (in shares)					3,634
Repurchase of common stock	(229,540)				$ (229,540)		(229,540)
Stock options exercised (in shares)		286
Stock options exercised	14,357		14,357				14,357
Non-vested shares awarded, net (in shares)		240
Non-vested shares awarded,net	925		925				925
Vesting of non-vested shares (in shares)					112
Vesting of non-vested shares	(7,646)				$ (7,646)		(7,646)
Share-based compensation	12,083		12,083				12,083
Cash dividends on common stock	(115,281)			(115,281)			(115,281)
Sale of non-controlling interest	5,500							5,500
Capital calls and distributions, net	(6,138)							(6,138)
Balance, end of period (in shares) at Dec. 31, 2015		74,530			8,636
Balance, end of period at Dec. 31, 2015	3,267,639	$ 4	982,009	2,704,121	$ (477,165)	21,587	3,230,556	37,083
Net income	232,281			232,668			232,668	(387)
Other comprehensive loss	(32,554)					(32,554)	(32,554)
Repurchase of common stock (in shares)					1,005
Repurchase of common stock	(66,792)				$ (66,792)		(66,792)
Stock options exercised (in shares)		214
Stock options exercised	12,465		12,465				12,465
Non-vested shares awarded, net (in shares)		249
Non-vested shares awarded,net	1,590		1,590				1,590
Vesting of non-vested shares (in shares)					15
Vesting of non-vested shares	(95)				$ (95)		(95)
Share-based compensation	10,471		10,471				10,471
Cash dividends on common stock	(113,455)			(113,455)			(113,455)
Capital calls and distributions, net	(5,193)							(5,193)
Balance, end of period (in shares) at Dec. 31, 2016		74,993			9,656
Balance, end of period at Dec. 31, 2016	3,306,357	$ 4	1,006,535	2,823,334	$ (544,052)	(10,967)	3,274,854	31,503
Net income	335,685			334,644			334,644	1,041
Other comprehensive loss	(18,657)					(18,657)	(18,657)
Repurchase of common stock (in shares)					80
Repurchase of common stock	(7,403)				$ (7,403)		(7,403)
Stock options exercised (in shares)		100
Stock options exercised	5,758		5,758				5,758
Non-vested shares awarded, net (in shares)		55
Non-vested shares awarded,net	0		0				0
Vesting of non-vested shares (in shares)					17
Vesting of non-vested shares	(1,390)				$ (1,390)		(1,390)
Share-based compensation	23,602		23,602				23,602
Cash dividends on common stock	(116,041)			(116,041)			(116,041)
Capital calls and distributions, net	(9,577)							(9,577)
Reclassification of stranded accumulated other comprehensive loss to retained earnings related to tax reform	(6,550)			6,550		(6,550)
Balance, end of period (in shares) at Dec. 31, 2017		75,148			9,753
Balance, end of period at Dec. 31, 2017	$ 3,518,334	$ 4	$ 1,035,895	$ 3,048,487	$ (552,845)	$ (36,174)	$ 3,495,367	$ 22,967

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash Flows From Operating Activities: [Abstract]
Net income	$ 335,685	$ 232,281	$ 292,259
Adjustments to reconcile net income to net cash provided by (used in) operating activities: [Abstract]
Provision for credit losses	(7,000)	65,000	34,000
Change in fair value of mortgage servicing rights due to market changes	(172)	2,193	4,853
Change in fair value of mortgage servicing rights due to loan runoff	33,527	40,744	28,064
Net unrealized losses from derivative contracts	3,704	11,234	964
Depreciation and amortization	54,466	47,016	37,918
Share-based compensation	23,602	10,471	12,083
Net amortization of securities discounts and premiums	28,693	41,643	55,145
Net realized gains on financial instruments and other net gains	(2,828)	(13,011)	(15,212)
Net gain on mortgage loans held for sale	(47,159)	(63,636)	(75,780)
Mortgage loans originated for sale	(3,286,873)	(6,117,417)	(6,372,956)
Proceeds from sale of mortgage loans held for sale	3,405,890	6,193,587	6,446,659
Capitalized mortgage servicing rights	(39,149)	(71,405)	(79,546)
Change in trading and fair value option securities	(804,204)	149,921	(69,298)
Change in receivables	321,880	(603,861)	(6,943)
Change in other assets	(5,506)	(49,565)	(29,548)
Change in accrued interest, taxes and expense	18,191	44,269	17,517
Change in other liabilities	182,184	(11,413)	15,756
Net cash provided by (used in) operating activities	214,931	(91,949)	295,935
Cash Flows From Investing Activities: [Abstract]
Proceeds from sales of available for sale securities	1,309,215	899,381	1,600,380
Proceeds from maturities or redemptions of investment securities	112,022	86,847	72,664
Proceeds from maturities or redemptions of available for sale securities	1,841,217	1,740,226	1,542,517
Purchases of investment securities	(32,972)	(41,590)	(25,132)
Purchases of available for sale securities	(2,845,557)	(2,333,740)	(3,300,601)
Change in amount receivable on unsettled securities sales	(68,792)	33,005	34,066
Loans originated, net of principal collected	(78,232)	(621,605)	(1,681,035)
Net payments on derivative asset contracts	479,409	(103,668)	(156,419)
Proceeds from disposition of assets	274,029	198,922	195,760
Acquisitions, net of cash acquired	0	56,017	(18,098)
Purchases of assets	(250,783)	(199,802)	(265,406)
Net cash provided by (used in) investing activities	739,556	(286,007)	(2,001,304)
Cash Flows From Financing Activities: [Abstract]
Net change in demand deposits, transaction deposits and savings accounts	(563,406)	1,277,285	149,951
Net change in time deposits	(123,384)	(216,084)	(202,652)
Net change in other borrowed funds	(10,909)	(606,476)	2,547,688
Repayment of subordinated debentures	0	226,550	121,810
Issuance of subordinated debentures, net of issuance costs	0	144,615	0
Change in amount due on unsettled security purchases	144,690	(10,389)	(273,643)
Issuance of common and treasury stock, net	4,368	12,455	6,711
Net change in derivative margin accounts	(17,726)	(28,806)	(43,226)
Net payments or proceeds on derivative liability contracts	(485,119)	106,051	149,428
Sale of non-controlling interests	0	0	5,500
Repurchase of common stock	(7,403)	(66,792)	(229,540)
Dividends paid	(116,041)	(113,455)	(115,281)
Net cash provided by (used in) financing activities	(1,174,930)	271,854	1,873,126
Net increase (decrease) in cash and cash equivalents	(220,443)	(106,102)	167,757
Cash and cash equivalents at beginning of period	2,537,497	2,643,599	2,475,842
Cash and cash equivalents at end of period	2,317,054	2,537,497	2,643,599
Supplemental Cash Flow Information: [Abstract]
Cash paid for interest	127,513	82,876	66,091
Cash paid for taxes	121,697	79,883	101,991
Net loans and bank premises transferred to repossessed real estate and other assets	7,367	36,391	12,592
Residential mortgage loans guaranteed by U.S. government agencies that became eligible for repurchase during the period	148,107	120,406	123,383
Conveyance of other real estate owned guaranteed by U.S. government agencies	$ 40,528	$ 68,873	$ 110,505

Significant Accounting Policies

Significant Accounting Policies	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Significant Accounting Policies [Text Block]	Significant Accounting Policies Basis of Presentation The Consolidated Financial Statements of BOK Financial Corporation (“BOK Financial” or “the Company”) have been prepared in conformity with accounting principles generally accepted in the United States ("U.S. GAAP"), including interpretations of U.S. GAAP issued by federal banking regulators and general practices of the banking industry. The Consolidated Financial Statements include the accounts of BOK Financial and its subsidiaries, principally BOKF, NA, BOK Financial Securities, Inc., The Milestone Group, Inc. and Cavanal Hill Distributors, Inc. All significant intercompany transactions are eliminated in consolidation. The Consolidated Financial Statements include the assets, liabilities, non-controlling interests and results of operations of variable interest entities (“VIEs”) when BOK Financial is determined to be the primary beneficiary. Variable interest entities are generally defined as entities that either do not have sufficient equity to finance their activities without support from other parties or whose equity investors lack a controlling financial interest. See additional discussion of variable interest entities at Note 14 following. Certain prior year amounts have been reclassified to conform to current year presentation. Check card revenue of $19.3 million in 2016 and $19.0 million in 2015 were reclassified from transaction card revenue to deposit service charges and fees. Nature of Operations BOK Financial, through its subsidiaries, provides a wide range of financial services to commercial and industrial customers, other financial institutions, municipalities, and consumers. These services include depository and cash management; lending and lease financing; mortgage banking; securities brokerage, trading and underwriting; and personal and corporate trust. BOKF, NA ("the Bank") operates as Bank of Oklahoma primarily in the Tulsa and Oklahoma City metropolitan areas of the state of Oklahoma and Bank of Texas primarily in the Dallas, Fort Worth and Houston metropolitan areas of the state of Texas. In addition, BOKF, NA does business as Bank of Albuquerque in Albuquerque, New Mexico; Colorado State Bank and Trust in Denver, Colorado; Bank of Arizona in Phoenix, Arizona; Mobank in Kansas City, Missouri/Kansas and Bank of Arkansas in Northwest Arkansas. BOKF, NA also operates the TransFund electronic funds network, Cavanal Hill Investment Management, and BOK Financial Asset Management, Inc. Use of Estimates Preparation of BOK Financial's Consolidated Financial Statements requires management to make estimates of future economic activities, including loan collectability, prepayments and cash flows from customer accounts. These estimates are based upon current conditions and information available to management. Actual results may differ significantly from these estimates. Acquisitions Assets and liabilities acquired, including identifiable intangible assets, are recorded at fair value on the acquisition date. The purchase price includes consideration paid at closing and the estimated fair value of contingent consideration that will be paid in the future, subject to achieving defined performance criteria. Premiums and discounts assigned to interest-earning assets and interest-bearing liabilities are amortized over the lives of the acquired assets and liabilities on either an individual instrument or pool basis. Provision for credit losses is recognized for changes in credit quality after the acquisition date. Goodwill is recognized as the excess of the purchase price over the net fair value of assets acquired and liabilities assumed. The Consolidated Statements of Earnings include the results of operations from the acquisition date. Goodwill and Intangible Assets Goodwill and intangible assets generally result from business combinations and are evaluated for each of BOK Financial's reporting units for impairment annually or more frequently if conditions indicate impairment. The evaluation of possible impairment of goodwill and intangible assets involves significant judgment based upon short-term and long-term projections of future performance. Reporting units are defined by the Company as significant lines of business within each operating segment. This definition is consistent with the manner in which the chief operating decision maker assesses the performance of the Company and makes decisions concerning the allocation of resources. The Company qualitatively assesses whether it is more likely than not that the fair value of the reporting units are less than their carrying value, including goodwill. Reporting unit carrying value includes sufficient capital to exceed regulatory requirements. This assessment includes consideration of relevant events and circumstances including but not limited to macroeconomic conditions, industry and market conditions, the financial and stock performance of the Company and other relevant factors. If the Company concludes based on the qualitative assessment that goodwill may be impaired, a quantitative one-step impairment test will be applied to goodwill at all reporting units. The quantitative analysis compares the fair value of the reporting unit with its carrying value, including goodwill. The fair value of each reporting unit is estimated by the discounted future earnings method. Goodwill is considered impaired if the fair value of the reporting unit is less than the carrying value of the reporting unit, including goodwill. Intangible assets are generally composed of customer relationships, naming rights, non-compete agreements and core deposit premiums. They are amortized using accelerated or straight-line methods, as appropriate, over the estimated benefit periods. These periods range from 3 years to 20 years . The net book values of identifiable intangible assets are evaluated for impairment when economic conditions indicate impairment may exist. Cash Equivalents Due from banks, funds sold (generally federal funds sold for one day), resell agreements (which generally mature within one to 30 days ) and investments in money market funds are considered cash equivalents. Securities Securities are identified as trading, investment (held to maturity) or available for sale at the time of purchase based upon the intent of management, liquidity and capital requirements, regulatory limitations and other relevant factors. Trading securities, which are acquired for profit through resale, are carried at fair value with unrealized gains and losses included in current period earnings. Investment securities are carried at amortized cost. Amortization is computed by methods that approximate level yield and is adjusted for changes in prepayment estimates. Securities identified as available for sale are carried at fair value. Unrealized gains and losses are recorded, net of deferred income taxes, as accumulated other comprehensive income in shareholders' equity. Available for sale securities are separately identified as pledged to creditors if the creditor has the right to sell or re-pledge the collateral. The purchase or sale of securities is recognized on a trade date basis. Realized gains and losses on sales of securities are based upon specific identification of the security sold. A receivable or payable is recognized for subsequent transaction settlement. Securities meeting certain criteria may also be transferred from the available for sale classification to the investment securities portfolio at fair value on the date of transfer. The unrealized gain or loss at the date of transfer is retained in accumulated other comprehensive income and in the carrying value of the investment securities portfolio. Such amounts are amortized over the estimated remaining life of the security as an adjustment to yield, offsetting the related amortization of the premium or accretion of the discount on the transferred securities. On a quarterly basis, the Company performs separate evaluations of impaired debt investment and available for sale securities and equity available for sale securities to determine if the decline in fair value below the amortized cost is other-than-temporary. For debt securities, management determines whether it intends to sell or if it is more likely than not that it will be required to sell impaired securities. This determination considers current and forecasted liquidity requirements and securities portfolio management. If the Company intends to sell or it is more likely than not that it will be required to sell the impaired debt security, a charge is recognized against earnings for the entire unrealized loss. For all impaired debt securities for which there is no intent or expected requirement to sell, the evaluation considers all available evidence to assess whether it is more likely than not that all amounts due would not be collected according to the security's contractual terms. Impairment of debt securities rated investment grade by all nationally-recognized rating agencies is considered temporary unless specific contrary information is identified. Impairment of debt securities rated below investment grade by at least one of the nationally recognized rating agencies is evaluated based on projections of estimated cash flows. Any expected credit loss due to the inability to collect all amounts due according to the security's contractual terms is recognized as a charge against earnings. Any remaining unrealized loss related to other factors would be recognized in other comprehensive income, net of taxes. For equity securities, management evaluates various factors including cause, severity and duration of the decline in value of the security and prospects for recovery, as well as the Company's intent and ability not to sell the security until the fair value exceeds amortized cost. If an unrealized loss is determined to be other-than-temporary, a charge is recognized against earnings for the difference between the security's amortized cost and fair value. BOK Financial may elect to carry certain securities at fair value with changes in fair value recognized in current period income. These securities are held with the intent that gains or losses will offset changes in the fair value of mortgage servicing rights or certain derivative instruments. Restricted equity securities represent equity interests the Company is required to hold in the Federal Reserve Banks and Federal Home Loan Banks. Restricted equity securities are carried at cost as these securities do not have a readily determined fair value because ownership of these shares is restricted and they lack a market. Derivative Instruments Derivative instruments may be used by the Company as part of its internal risk management programs or may be offered to customers. All derivative instruments are carried at fair value and changes in fair value are generally reported in income as they occur. The determination of fair value of derivative instruments considers changes in interest rates, commodity prices and foreign exchange rates. Credit risk is also considered in determining fair value. Deterioration in the credit rating of customers or other counterparties reduces the fair value of asset contracts. Deterioration of our credit rating could decrease the fair value of our derivative liabilities. When bilateral netting agreements or similar agreements exist between the Company and its counterparties that create a single legal claim or obligation to pay or receive the net amount in settlement of the individual derivative contracts, the Company reports derivative assets and liabilities on a net by derivative contract by counterparty basis. Derivative contracts may also require the Company to provide or receive cash margin as collateral for derivative assets and liabilities. Derivative assets and liabilities are reported net of cash margin when certain conditions are met. In addition, derivative contracts executed with customers under Customer Risk Management Programs may be secured by non-cash collateral in conjunction with a credit agreement with that customer. Access to collateral in the event of default is reasonably assured. Derivative instruments may be designated as cash flow hedges of variable rate assets or liabilities, or of anticipated transactions. Changes in the fair value of derivative instruments designated as cash flow hedges are recorded in accumulated other comprehensive income to the extent they are effective. The amount recorded in other comprehensive income is reclassified to earnings in the same periods as the hedged cash flows impact earnings. The ineffective portion of changes in fair value is reported in current earnings. BOK Financial may use derivative instruments in managing its interest rate sensitivity, as part of its economic hedge of the changes in the fair value of mortgage servicing rights and to mitigate the market risk of holding trading securities. Changes in the fair value of derivative instruments used in managing interest rate sensitivity and as part of its economic hedge of changes in the fair value of mortgage servicing rights are included in Other Operating Revenue - Gain (loss) on derivatives, net in the Consolidated Statements of Earnings. Changes in the fair value of derivative instruments used to mitigate the market risk of holding trading securities are included in Operating Revenue - Brokerage and trading revenue. BOK Financial also enters into mortgage loan commitments that are considered derivative contracts. Forward sales contracts that have not been designated as hedging instruments are used to economically hedge these mortgage loan commitments as well as mortgage loans held for sale. Mortgage loan commitments are carried at fair value based upon quoted prices. Changes in the fair value of mortgage loan commitments, mortgage loans held for sale and forward sales contracts are reported in Other Operating Revenue - Mortgage Banking Revenue. BOK Financial offers programs that permit its customers to manage various risks, including fluctuations in energy, cattle and other agricultural products, interest rates and foreign exchange rates with derivative contracts. Customers may also manage interest rate risk through interest rate swaps used by the borrower to modify interest rate terms of their loans or to-be-announced securities used by our mortgage banking customers to hedge their loan production. Derivative contracts are executed between the customers and BOK Financial. Offsetting contracts are executed between BOK Financial and other selected counterparties to minimize market risk from changes in commodity prices, interest rates or foreign exchange rates. The counterparty contracts are identical to customer contracts, except for a fixed pricing spread or fee paid to BOK Financial as profit and compensation for administrative costs and credit risk which is recognized over the life of the contracts and included in other Operating Revenue - Brokerage and Trading Revenue in the Consolidated Statements of Earnings. Loans Loans are either secured or unsecured based on the type of loan and the financial condition of the borrower. Repayment is generally expected from cash flow or proceeds from the sale of selected assets of the borrower. BOK Financial is exposed to risk of loss on loans due to the borrower's financial difficulties, which may arise from any number of factors, including problems within the respective industry or local economic conditions. Access to collateral, in the event of borrower default, is reasonably assured through adherence to applicable lending laws and through sound lending standards and credit review procedures. Accounting policies for all loans, excluding residential loans guaranteed by U.S. government agencies, are as follows. Interest is accrued at the applicable interest rate on the outstanding principal amount. Loans are placed on nonaccruing status when, in the opinion of management, full collection of principal or interest is uncertain. Internally risk graded loans are individually evaluated for nonaccruing status quarterly. Non-risk graded loans are generally placed on nonaccruing status when 90 days or more past due or within 60 days of being notified of the borrower's bankruptcy filing. Interest previously accrued but not collected is charged against interest income when the loan is placed on nonaccruing status. Payments received on nonaccruing loans are applied to principal or recognized as interest income, according to management's judgment as to the collectability of principal. Loans may be returned to accruing status when, in the opinion of management, full collection of principal and interest, including principal previously charged off, is probable based on improvements in the borrower's financial condition or a sustained period of performance. Loans to borrowers experiencing financial difficulties may be modified in troubled debt restructurings ("TDRs"). All TDRs are classified as nonaccruing. Modifications generally consist of extension of payment terms or interest rate concessions and may result either voluntarily through negotiations with the borrower or involuntarily through court order. Generally, principal and accrued but unpaid interest is not voluntarily forgiven. Performing loans may be renewed under the current collateral, debt service ratio and other underwriting standards. Nonaccruing loans may also be renewed and will remain classified as nonaccruing. Occasionally, loans, other than residential mortgage loans, may be held for sale in order to manage credit concentration. These loans are carried at the lower of cost or fair value with gains or losses recognized in gain (loss) on assets. All loans are charged-off when the loan balance or a portion of the loan balance is no longer supported by the paying capacity of the borrower or when the required cash flow is reduced in a TDR. The charge-off amount is determined through an evaluation of available cash resources and collateral value. Internally risk graded loans are evaluated quarterly and charge-offs are taken in the quarter in which the loss is identified. Non-risk graded loans that are past due between 60 days and 180 days , based on the loan product type, are charged off. Loans to borrowers whose personal obligation has been discharged through Chapter 7 bankruptcy proceedings are charged off within 60 days of notice of the bankruptcy filing, regardless of payment status. Loan origination and commitment fees and direct loan acquisition and origination costs are deferred and amortized as an adjustment to yield over the life of the loan or over the commitment period, as applicable. Amortization does not anticipate loan prepayments. Net unamortized fees are recognized in full at time of payoff. Qualifying residential mortgage loans guaranteed by U.S. government agencies have been sold into GNMA pools. Under certain performance conditions specified in government programs, the Company has the right, but not the obligation to repurchase loans from GNMA pools. These loans no longer qualify for sale accounting and are recognized in the Consolidated Balance Sheet. Guaranteed loans are considered to be impaired because we do not expect to receive all principal and interest based on the loan's contractual terms. The principal balance continues to be guaranteed, however, interest accrues at a curtailed rate as specified in the programs. The carrying value of these loans is reduced based on an estimate of expected cash flows discounted at the original note rate plus a liquidity spread. Guaranteed loans may be modified in TDRs in accordance with U.S. government agency guidelines. Interest continues to accrue at the modified rate. U.S. government guaranteed loans may either be resold into GNMA pools after a performance period specified by the programs or foreclosed and conveyed to the guarantors. Loans are disaggregated into portfolio segments and further disaggregated into classes. The portfolio segment is the level at which the Company develops and documents a systematic method for determining its Allowance for Credits Losses. Classes are based on the risk characteristics of the loans and the Company's method for monitoring and assessing credit risk. Allowance for Loan Losses and Accrual for Off-Balance Sheet Credit Risk The appropriateness of the allowance for loan losses and accrual for off-balance sheet credit risk (collectively "Allowance for Credit Losses") is assessed by management quarterly based on an ongoing quarterly evaluation of the probable estimated losses inherent in the portfolio, including probable losses on outstanding loans and unused commitments to provide financing. A consistent well-documented methodology has been developed and is applied by an independent Credit Administration department to assure consistency across the Company. The allowance for loan losses consists of specific allowances attributed to impaired loans that have not yet been charged down to amounts we expect to recover, general allowances based on estimated loss rates by loan class and nonspecific allowances based on factors that affect more than one portfolio segment. There were no changes to the methodology for estimating general allowances during 2017 or 2016 . Loans are considered to be impaired when it becomes probable that BOK Financial will be unable to collect all amounts due according to the contractual terms of the loan agreements. Internally risk graded loans are evaluated individually for impairment. Substantially all commercial and commercial real estate loans and certain residential mortgage and personal loans are risk graded based on a quarterly evaluation of the borrowers' ability to repay. Certain commercial loans and most residential mortgage and personal loans are small balance, homogeneous pools of loans that are not risk graded. Non-risk graded loans are identified as impaired based on performance status. Generally, non-risk graded loans 90 days or more past due, modified in a troubled debt restructuring or in bankruptcy are considered to be impaired. Specific allowances for impaired loans are measured by an evaluation of estimated future cash flows discounted at the loan's initial effective interest rate or the fair value of collateral for certain collateral dependent loans. The fair value of real property held as collateral is generally based on third party appraisals that conform to Uniform Standards of Professional Appraisal Practice, less estimated selling costs. Appraised values are on an “as-is” basis and generally are not adjusted by the Company. Updated appraisals are obtained at least annually or more frequently if market conditions indicate collateral values may have declined. Collateral value of mineral rights is generally determined by our internal staff of engineers based on projected cash flows from proven oil and gas reserves under existing economic and operating conditions. The value of other collateral is generally determined by our special assets staff based on projected liquidation cash flows under current market conditions. Collateral values and available cash resources that support impaired loans are evaluated quarterly. Historical statistics may be used as a practical way to estimate impairment in limited situations, such as when a collateral dependent loan is identified as impaired at the end of a reporting period until an appraisal of collateral value is received or a full assessment of future cash flows is completed. Estimates of future cash flows and collateral values require significant judgments and may be volatile. General allowances for unimpaired loans are based on an estimated loss rate by loan class. The appropriate historical gross loss rate for each loan class is determined by the greater of the current loss rate based on the most recent twelve months or a ten-year average gross loss rate. Recoveries are not directly considered in the estimation of historical loss rates. Recoveries generally do not follow predictable patterns and are not received until well-after the charge-off date as a result of protracted legal actions. For risk graded loans, historical gross loss rates are adjusted for changes in risk grading. For each loan class, the current weighted average risk grade is compared to the long-term weighted average risk grade. This comparison determines whether credit risk in each loan class is increasing or decreasing. Historical loss rates are adjusted upward or downward in proportion to changes in average risk grading. General allowances for unimpaired loans also consider inherent risks identified for each loan class. Inherent risks consider loss rates that most appropriately represent the current credit cycle and other factors attributable to a specific loan class which have not yet been represented in the historical gross loss rates or risk grading. These factors include changes in commodity prices or engineering imprecision which may affect the value of reserves that secure our energy loan portfolio, construction risk that may affect commercial real estate loans, changes in regulations and public policy that may disproportionately impact health care loans and changes in loan products. Nonspecific allowances are maintained for risks beyond factors specific to a particular portfolio segment or loan class. These factors include trends in the economy in our primary lending areas, concentration in large-balance loans and other relevant factors. An accrual for off-balance sheet credit risk is included in Other liabilities. The appropriateness of the accrual is determined in the same manner as the allowance for loan losses. A provision for credit losses is charged against or credited to earnings in amounts necessary to maintain an appropriate Allowance for Credit Losses. Recoveries of loans previously charged off are added to the allowance when received. Real Estate and Other Repossessed Assets Real estate and other repossessed assets are acquired in partial or total forgiveness of loans. These assets are initially recognized at cost, which is determined by fair value at date of foreclosure less estimated disposal costs. They are subsequently carried at the lower of cost or current fair value less estimated disposal costs. Decreases in fair value below cost are recognized as asset-specific valuation allowances which may be reversed when supported by future increases in fair value. Subsequent increases in fair value may be used to reduce the allowance but not below zero. Fair values of real estate are based on “as is” appraisals which are updated at least annually or more frequently for certain asset types or assets located in certain distressed markets. Fair values based on appraisals are generally considered to be based on significant other observable inputs. The Company also considers decreases in listing price and other relevant information in quarterly evaluations and reduces the carrying value of real estate and other repossessed assets when necessary. Fair values based on list prices and other relevant information are generally considered to be based on significant unobservable inputs. Additional costs incurred to complete real estate and other repossessed assets may increase the carrying value, up to current fair value based on “as completed” appraisals. The fair value of mineral rights included in repossessed assets are generally determined by our internal staff of engineers based on projected cash flows from proven oil and gas reserves under existing economic and operating conditions. The value of other repossessed assets is generally determined by our special assets staff based on projected liquidation cash flows under current market conditions. Income generated by these assets is recognized as received. Operating expenses are recognized as incurred. Gains or losses on sales of real estate and other repossessed assets are based on the cash proceeds received less the cost basis of the asset, net of any valuation allowances. The estimated disposal costs of real estate and other repossessed assets are evaluated by the Company on an annual basis based on actual results. Transfers of Financial Assets BOK Financial regularly transfers financial assets as part of its mortgage banking activities and periodically may transfer other financial assets. Transfers are recorded as sales when the criteria for surrender of control are met. The Company has elected to carry certain residential mortgage loans held for sale at fair value under the fair value option. Changes in fair value are recognized in net income as they occur. These loans are reported separately in the Consolidated Balance Sheets and changes in fair value are recorded in other operating revenue - mortgage banking revenue in the Consolidated Statements of Earnings. Fair value of conforming residential mortgage loans that will be sold to U.S. government agencies is based on sales commitments or market quotes considered Level 2 inputs. Fair value of mortgage loans that are unable to be sold to U.S. government agencies is based on Level 3 inputs using quoted prices of loans that are sold in securitization transactions with a liquidity discount applied. The fair value is corroborated with an independent third party on at least an annual basis. BOK Financial retains a repurchase obligation under underwriting representations and warranties related to residential mortgage loans transferred and generally retains the right to service the loans. The Company may incur a recourse obligation in limited circumstances. Separate accruals are recognized in Other liabilities in the Consolidated Balance Sheets for repurchase and recourse obligations. These reserves reflect the estimated amount of probable loss the Company will incur as a result of repurchasing a loan, indemnifications, and other settlement resolutions. Repurchases of loans with an origination defect that are also credit impaired are considered collateral dependent and are initially recognized at net realizable value (appraised value less the cost to sell). The difference between unpaid principal balance and net realizable value is not accreted. Repurchases of loans with an origination defect that are not credit impaired are carried at fair value as of the repurchase date. Interest income continues to accrue on these loans and the discount is accreted over the estimated life of the loan. The Company may also choose to purchase GNMA loans once certain mandated delinquency criteria are met. The loans that are eligible and are chosen to be repurchased are initially recognized at fair value based on expected cash flow discounted using the average agency guaranteed debenture rates, average actual principal loss rates and liquidity premium. Mortgage Servicing Rights Mortgage servicing rights may be purchased or may be recognized when mortgage loans are originated and sold with servicing rights retained. All mortgage servicing rights are carried at fair value. Changes in the fair value are recognized in earnings as they occur. Mortgage servicing rights are not traded in active markets. A cash flow model is used to determine fair value. Key assumptions and estimates, including projected prepayment speeds and assumed servicing costs, earnings on escrow deposits, ancillary income and discount rates, used by this model are based on current market sources. Assumptions used to value mortgage servicing rights are considered significant unobservable inputs. A separate third party model is used to estimate prepayment speeds based on interest rates, housing turnover rates, estimated loan curtailment, anticipated defaults and other relevant factors. The prepayment model is updated daily for changes in market conditions and adjusted to better correlate with actual performance of BOK Financial's servicing portfolio. Fair value estimates from outside sources are received at least annually to corroborate the results of the valuation model. Premises and Equipment Premises and equipment are carried at cost, including capitalized interest when appropriate, less accumulated depreciation and amortization. Depreciation and amortization are computed on a straight-line basis over the estimated useful lives of the assets or, for leasehold improvements, over the shorter of the estimated useful lives or remaining lease terms. Useful lives range from 5 years to 40 years for buildings and improvements, 3 years to 10 years for software and 3 years to 10 years for furniture and equipment. Construction in progress represents facilities construction and data processing systems projects underway that have not yet been placed into service. D

Securities

Securities	12 Months Ended
	Dec. 31, 2017
Marketable Securities [Abstract]
Securities [Text Block]	Securities Trading Securities The fair value and net unrealized gain (loss) included in trading securities is as follows (in thousands): December 31, 2017 December 31, 2016 Fair Value Net Unrealized Gain (Loss) Fair Value Net Unrealized Gain (Loss) U.S. government agency debentures $ 21,196 $ 8 $ 6,234 $ (4 ) U.S. government agency residential mortgage-backed securities 392,673 (517 ) 310,067 635 Municipal and other tax-exempt securities 13,559 83 14,427 50 Asset-backed securities 23,885 (26 ) — — Other trading securities 11,363 4 6,900 57 Total trading securities $ 462,676 $ (448 ) $ 337,628 $ 738 Investment Securities The amortized cost and fair values of investment securities are as follows (in thousands): December 31, 2017 Amortized Fair Gross Unrealized Cost Value Gain Loss Municipal and other tax-exempt securities $ 228,186 $ 230,349 $ 2,967 $ (804 ) U.S. government agency residential mortgage-backed securities – Other 15,891 16,242 446 (95 ) Other debt securities 217,716 233,444 17,095 (1,367 ) Total investment securities $ 461,793 $ 480,035 $ 20,508 $ (2,266 ) December 31, 2016 Amortized Fair Gross Unrealized Cost Value Gain Loss Municipal and other tax-exempt securities $ 320,364 $ 321,225 $ 2,272 $ (1,411 ) U.S. government agency residential mortgage-backed securities – Other 20,777 21,473 767 (71 ) Other debt securities 205,004 222,795 18,115 (324 ) Total investment securities $ 546,145 $ 565,493 $ 21,154 $ (1,806 ) The amortized cost and fair values of investment securities at December 31, 2017 , by contractual maturity, are as shown in the following table (dollars in thousands): Less than One Year One to Five Years Six to Ten Years Over Ten Years Total Weighted Average Maturity² Municipal and other tax-exempt securities: Carrying value $ 102,569 $ 74,738 $ 14,929 $ 35,950 $ 228,186 3.51 Fair value 102,414 74,467 15,538 37,930 230,349 Nominal yield¹ 1.82 % 2.34 % 5.06 % 5.19 % 2.73 % Other debt securities: Carrying value $ 13,996 $ 51,502 $ 135,233 $ 16,985 $ 217,716 6.23 Fair value 14,058 53,827 149,517 16,042 233,444 Nominal yield 4.24 % 4.75 % 5.69 % 4.36 % 5.27 % Total fixed maturity securities: Carrying value $ 116,565 $ 126,240 $ 150,162 $ 52,935 $ 445,902 4.83 Fair value 116,472 128,294 165,055 53,972 463,793 Nominal yield 2.11 % 3.32 % 5.63 % 4.92 % 3.97 % Residential mortgage-backed securities: Carrying value $ 15,891 ³ Fair value 16,242 Nominal yield 4 2.76 % Total investment securities: Carrying value $ 461,793 Fair value 480,035 Nominal yield 3.93 % 1 Calculated on a taxable equivalent basis using a 39% effective tax rate. 2 Expected maturities may differ from contractual maturities because borrowers may have the right to call or prepay obligations with or without penalty. 3 The average expected lives of residential mortgage-backed securities were 4.8 years based upon current prepayment assumptions. 4 The nominal yield on residential mortgage-backed securities is based upon prepayment assumptions at the purchase date. Actual yields earned may differ significantly based upon actual prepayments. See Quarterly Financial Summary - Unaudited for current yields on the investment securities portfolio. Available for Sale Securities The amortized cost and fair value of available for sale securities are as follows (in thousands): December 31, 2017 Amortized Fair Gross Unrealized Cost Value Gain Loss OTTI U.S. Treasury securities $ 1,000 $ 1,000 $ — $ — $ — Municipal and other tax-exempt securities 27,182 27,080 181 (283 ) — Residential mortgage-backed securities: U.S. government agencies: FNMA 3,021,551 2,997,563 11,549 (35,537 ) — FHLMC 1,545,971 1,531,009 3,148 (18,110 ) — GNMA 787,626 780,580 1,607 (8,653 ) — Total U.S. government agencies 5,355,148 5,309,152 16,304 (62,300 ) — Private issue 74,311 93,221 19,301 — (391 ) Total residential mortgage-backed securities 5,429,459 5,402,373 35,605 (62,300 ) (391 ) Commercial mortgage-backed securities guaranteed by U.S. government agencies 2,858,885 2,834,961 1,963 (25,887 ) — Other debt securities 25,500 25,481 50 (69 ) — Perpetual preferred stock 12,562 15,767 3,205 — — Equity securities and mutual funds 14,487 14,916 515 (86 ) — Total available for sale securities $ 8,369,075 $ 8,321,578 $ 41,519 $ (88,625 ) $ (391 ) December 31, 2016 Amortized Fair Gross Unrealized Cost Value Gain Loss OTTI U.S. Treasury securities $ 1,000 $ 999 $ — $ (1 ) $ — Municipal and other tax-exempt securities 41,050 40,993 343 (400 ) — Residential mortgage-backed securities: U.S. government agencies: FNMA 3,062,525 3,055,676 25,066 (31,915 ) — FHLMC 1,534,451 1,531,116 8,475 (11,810 ) — GNMA 878,375 873,594 2,259 (7,040 ) — Total U.S. government agencies 5,475,351 5,460,386 35,800 (50,765 ) — Private issue 101,192 115,535 14,577 (16 ) (218 ) Total residential mortgage-backed securities 5,576,543 5,575,921 50,377 (50,781 ) (218 ) Commercial mortgage-backed securities guaranteed by U.S. government agencies 3,035,750 3,017,933 5,472 (23,289 ) — Other debt securities 4,400 4,152 — (248 ) — Perpetual preferred stock 15,561 18,474 2,913 — — Equity securities and mutual funds 17,424 18,357 1,060 (127 ) — Total available for sale securities $ 8,691,728 $ 8,676,829 $ 60,165 $ (74,846 ) $ (218 ) The amortized cost and fair values of available for sale securities at December 31, 2017 , by contractual maturity, are as shown in the following table (dollars in thousands): Less than One Year One to Five Years Six to Ten Years Over Ten Years Total Weighted Average Maturity 5 U.S. Treasury securities: Amortized cost $ 1,000 $ — $ — $ — $ 1,000 0.04 Fair value 1,000 — — — 1,000 Nominal yield 0.87 % — % — % — % 0.87 % Municipal and other tax-exempt securities: Amortized cost 9,008 2,680 — 15,494 27,182 9.15 Fair value 9,022 2,811 — 15,247 27,080 Nominal yield¹ 3.45 % 6.04 % — % 2.26 % 6 3.03 % Commercial mortgage-backed securities: Amortized cost 22,742 970,611 1,604,465 261,067 2,858,885 7.17 Fair value 22,667 965,099 1,590,107 257,088 2,834,961 Nominal yield 1.49 % 1.93 % 2.03 % 2.03 % 1.99 % Other debt securities: Amortized cost — — — 25,500 25,500 14.68 Fair value — — — 25,481 25,481 Nominal yield — % — % — % 1.59 % 1.59 % Total fixed maturity securities: Amortized cost $ 32,750 $ 973,291 $ 1,604,465 $ 302,061 $ 2,912,567 7.25 Fair value 32,689 967,910 1,590,107 297,816 2,888,522 Nominal yield 2.01 % 1.94 % 2.03 % 2.01 % 2.00 % Residential mortgage-backed securities: Amortized cost $ 5,429,459 2 Fair value 5,402,373 Nominal yield 4 2.04 % Perpetual preferred stock. equity securities and mutual funds: Amortized cost $ 27,049 ³ Fair value 30,683 Nominal yield — % Total available-for-sale securities: Amortized cost $ 8,369,075 Fair value 8,321,578 Nominal yield 2.02 % 1 Calculated on a taxable equivalent basis using a 39% effective tax rate. 2 The average expected lives of mortgage-backed securities were 4.2 years based upon current prepayment assumptions. 3 Primarily common stock and preferred stock of corporate issuers with no stated maturity. 4 The nominal yield on mortgage-backed securities is based upon prepayment assumptions at the purchase date. Actual yields earned may differ significantly based upon actual prepayments. See Quarterly Financial Summary –– Unaudited following for current yields on available for sale securities portfolio. 5 Expected maturities may differ from contractual maturities, because borrowers may have the right to call or prepay obligations with or without penalty. 6 Nominal yield on municipal and other tax-exempt securities and other debt securities with contractual maturity dates over ten years are based on variable rates which generally are reset within 35 days . Sales of available for sale securities resulted in gains and losses as follows (in thousands): Year Ended December 31, 2017 2016 2015 Proceeds $ 1,309,215 $ 899,381 $ 1,600,380 Gross realized gains 10,223 11,696 15,849 Gross realized losses (5,795 ) (21 ) (3,791 ) Related federal and state income tax expense 1,722 4,542 4,691 A summary of investment and available for sale securities that have been pledged as collateral for repurchase agreements, public trust funds on deposit and for other purposes, as required by law was as follows (in thousands): December 31, 2017 2016 Investment: Carrying value $ 226,852 $ 322,208 Fair value 229,429 323,808 Available for sale: Amortized cost 7,151,468 7,353,116 Fair value 7,089,346 7,327,470 The secured parties do not have the right to sell or re-pledge these securities. Temporarily Impaired Securities as of December 31, 2017 (In thousands) Number of Securities Less Than 12 Months 12 Months or Longer Total Fair Value Unrealized Loss Fair Value Unrealized Loss Fair Value Unrealized Loss Investment: Municipal and other tax-exempt securities 100 $ 145,960 $ 643 $ 5,833 $ 161 $ 151,793 $ 804 U.S. government agency residential mortgage-backed securities – Other 1 — — 3,356 95 3,356 95 Other debt securities 49 20,091 1,238 3,076 129 23,167 1,367 Total investment securities 150 $ 166,051 $ 1,881 $ 12,265 $ 385 $ 178,316 $ 2,266 Number of Securities Less Than 12 Months 12 Months or Longer Total Fair Value Unrealized Loss Fair Value Unrealized Loss Fair Value Unrealized Loss Available for sale: U.S. Treasury securities — $ — $ — $ — $ — $ — $ — Municipal and other tax-exempt securities 19 12,765 18 4,802 265 17,567 283 Residential mortgage-backed securities: U.S. government agencies: FNMA 113 1,203,041 9,618 824,029 25,919 2,027,070 35,537 FHLMC 69 863,778 7,297 385,816 10,813 1,249,594 18,110 GNMA 27 201,887 1,452 248,742 7,201 450,629 8,653 Total U.S. agencies 209 2,268,706 18,367 1,458,587 43,933 3,727,293 62,300 Private issue 1 8 5,898 391 — — 5,898 391 Total residential mortgage-backed securities 217 2,274,604 18,758 1,458,587 43,933 3,733,191 62,691 Commercial mortgage-backed securities guaranteed by U.S. government agencies 185 1,465,703 11,824 652,296 14,063 2,117,999 25,887 Other debt securities 2 19,959 41 472 28 20,431 69 Perpetual preferred stock — — — — — — — Equity securities and mutual funds 111 911 7 2,203 79 3,114 86 Total available for sale securities 534 $ 3,773,942 $ 30,648 $ 2,118,360 $ 58,368 $ 5,892,302 $ 89,016 1 Includes securities for which an unrealized loss remains in AOCI after an other-than-temporary credit loss has been recognized in income. Temporarily Impaired Securities as of December 31, 2016 (In thousands) Number of Securities Less Than 12 Months 12 Months or Longer Total Fair Value Unrealized Loss Fair Value Unrealized Loss Fair Value Unrealized Loss Investment: Municipal and other tax- exempt securities 151 $ 219,892 $ 1,316 $ 4,333 $ 95 $ 224,225 $ 1,411 U.S. government agency residential mortgage-backed securities – Other 1 4,358 71 — — 4,358 71 Other debt securities 41 11,820 322 855 2 12,675 324 Total investment securities 193 $ 236,070 $ 1,709 $ 5,188 $ 97 $ 241,258 $ 1,806 Number of Securities Less Than 12 Months 12 Months or Longer Total Fair Value Unrealized Loss Fair Value Unrealized Loss Fair Value Unrealized Loss Available for sale: U.S. Treasury securities 1 $ 999 $ 1 $ — $ — $ 999 $ 1 Municipal and other tax-exempt securities 24 15,666 22 4,689 378 20,355 400 Residential mortgage-backed securities: U. S. government agencies: FNMA 91 1,787,644 30,238 72,105 1,677 1,859,749 31,915 FHLMC 58 964,017 11,210 18,307 600 982,324 11,810 GNMA 31 548,637 6,145 25,796 895 574,433 7,040 Total U.S. agencies 180 3,300,298 47,593 116,208 3,172 3,416,506 50,765 Private issue 1 6 7,931 174 13,508 60 21,439 234 Total residential mortgage-backed securities 186 3,308,229 47,767 129,716 3,232 3,437,945 50,999 Commercial mortgage-backed securities guaranteed by U.S. government agencies 171 1,904,584 22,987 38,875 302 1,943,459 23,289 Other debt securities 2 — — 4,152 248 4,152 248 Perpetual preferred stock — — — — — — — Equity securities and mutual funds 104 2,127 41 817 86 2,944 127 Total available for sale securities 488 $ 5,231,605 $ 70,818 $ 178,249 $ 4,246 $ 5,409,854 $ 75,064 1 Includes securities for which an unrealized loss remains in AOCI after an other-than-temporary credit loss has been recognized in income. Based on separate evaluations of impaired debt and equity securities, including perpetual preferred stocks, as of December 31, 2017 , the Company does not intend to sell any impaired available for sale securities before fair value recovers to the current amortized cost and it is more-likely-than-not that the Company will not be required to sell impaired securities before fair value recovers, which may be maturity. No other-than-temporary impairment losses were recorded in earnings during 2017 and none were recorded in 2016 . Cumulative other-than-temporary impairment on available for sale securities was $55 million at December 31, 2017 . Fair Value Option Securities Fair value option securities represent securities which the Company has elected to carry at fair value and are separately identified on the Consolidated Balance Sheets with changes in the fair value recognized in earnings as they occur. Certain residential mortgage-backed securities issued by U.S. government agencies and derivative contracts are held as an economic hedge of the mortgage servicing rights. The fair value and net unrealized gain (loss) included in Fair value option securities is as follows (in thousands): December 31, 2017 December 31, 2016 Fair Value Net Unrealized Gain (Loss) Fair Value Net Unrealized Gain (Loss) U.S. government agency residential mortgage-backed securities $ 755,054 $ (1,877 ) $ 77,046 $ (1,777 ) Restricted Equity Securities Restricted equity securities include stock we are required to hold as members of the Federal Reserve system and the Federal Home Loan Banks ("FHLB"). Restricted equity securities are carried at cost as these securities do not have a readily determined fair value because ownership of these shares is restricted and they lack a market. A summary of restricted equity securities follows (in thousands): December 31, 2017 2016 Federal Reserve Bank stock $ 40,746 $ 36,498 Federal Home Loan Bank stock 279,200 270,541 Other 243 201 Total $ 320,189 $ 307,240

Derivatives

Derivatives	12 Months Ended
	Dec. 31, 2017
Derivative Instrument Detail [Abstract]
Derivatives [Text Block]	Derivatives The following table summarizes the fair values of derivative contracts recorded as “derivative contracts” assets and liabilities in the balance sheet at December 31, 2017 (in thousands): Assets Notional 1 Gross Fair Value Netting Adjustments Net Fair Value Before Cash Collateral Cash Collateral Fair Value Net of Cash Collateral Customer risk management programs: Interest rate contracts To-be-announced residential mortgage-backed securities $ 12,347,542 $ 23,606 $ (18,096 ) $ 5,510 $ — $ 5,510 Interest rate swaps 1,478,944 28,278 — 28,278 (4,964 ) 23,314 Energy contracts 1,190,067 103,044 (47,873 ) 55,171 (196 ) 54,975 Agricultural contracts 53,238 1,576 (960 ) 616 — 616 Foreign exchange contracts 132,397 129,551 — 129,551 (448 ) 129,103 Equity option contracts 99,633 5,503 — 5,503 (920 ) 4,583 Total customer risk management programs 15,301,821 291,558 (66,929 ) 224,629 (6,528 ) 218,101 Internal risk management programs 4,736,701 9,494 (7,093 ) 2,401 — 2,401 Total derivative contracts $ 20,038,522 $ 301,052 $ (74,022 ) $ 227,030 $ (6,528 ) $ 220,502 Liabilities Notional¹ Gross Fair Value Netting Adjustments Net Fair Value Before Cash Collateral Cash Collateral Fair Value Net of Cash Collateral Customer risk management programs: Interest rate contracts To-be-announced residential mortgage-backed securities $ 11,537,742 $ 20,367 $ (18,096 ) $ 2,271 $ (704 ) $ 1,567 Interest rate swaps 1,478,944 28,298 — 28,298 (12,896 ) 15,402 Energy contracts 1,166,924 101,603 (47,873 ) 53,730 (42,767 ) 10,963 Agricultural contracts 48,552 1,551 (960 ) 591 — 591 Foreign exchange contracts 126,251 123,321 — 123,321 (53 ) 123,268 Equity option contracts 99,633 5,503 — 5,503 — 5,503 Total customer risk management programs 14,458,046 280,643 (66,929 ) 213,714 (56,420 ) 157,294 Internal risk management programs 5,728,421 21,762 (7,093 ) 14,669 — 14,669 Total derivative contracts $ 20,186,467 $ 302,405 $ (74,022 ) $ 228,383 $ (56,420 ) $ 171,963 1 Notional amounts for commodity contracts are converted into dollar-equivalent amounts based on dollar prices at the inception of the contract. The following table summarizes the fair values of derivative contracts recorded as “derivative contracts” assets and liabilities in the balance sheet at December 31, 2016 (in thousands): Assets Notional 1 Gross Fair Value Netting Adjustments Net Fair Value Before Cash Collateral Cash Collateral Fair Value Net of Cash Collateral Customer risk management programs: Interest rate contracts To-be-announced residential mortgage-backed securities $ 16,949,152 $ 180,695 $ (60,555 ) $ 120,140 $ — $ 120,140 Interest rate swaps 1,403,408 34,442 — 34,442 (4,567 ) 29,875 Energy contracts 835,566 64,140 (28,298 ) 35,842 (71 ) 35,771 Agricultural contracts 53,209 1,382 (515 ) 867 — 867 Foreign exchange contracts 580,886 494,349 — 494,349 (5,183 ) 489,166 Equity option contracts 100,924 4,357 — 4,357 (730 ) 3,627 Total customer risk management programs 19,923,145 779,365 (89,368 ) 689,997 (10,551 ) 679,446 Internal risk management programs 2,514,169 10,426 — 10,426 — 10,426 Total derivative contracts $ 22,437,314 $ 789,791 $ (89,368 ) $ 700,423 $ (10,551 ) $ 689,872 Liabilities Notional¹ Gross Fair Value Netting Adjustments Net Fair Value Before Cash Collateral Cash Collateral Fair Value Net of Cash Collateral Customer risk management programs: Interest rate contracts To-be-announced residential mortgage-backed securities $ 16,637,532 $ 176,928 $ (60,555 ) $ 116,373 $ — $ 116,373 Interest rate swaps 1,403,408 34,442 — 34,442 (11,977 ) 22,465 Energy contracts 820,365 64,306 (28,298 ) 36,008 (31,534 ) 4,474 Agricultural contracts 53,216 1,365 (515 ) 850 (769 ) 81 Foreign exchange contracts 580,712 494,695 — 494,695 (3,630 ) 491,065 Equity option contracts 100,924 4,357 — 4,357 — 4,357 Total customer risk management programs 19,596,157 776,093 (89,368 ) 686,725 (47,910 ) 638,815 Internal risk management programs 2,582,202 25,716 — 25,716 — 25,716 Total derivative contracts $ 22,178,359 $ 801,809 $ (89,368 ) $ 712,441 $ (47,910 ) $ 664,531 1 Notional amounts for commodity contracts are converted into dollar-equivalent amounts based on dollar prices at the inception of the contract. The following summarizes the pre-tax net gains (losses) on derivative instruments and where they are recorded in the Consolidated Statements of Earnings (in thousands): Year Ended December 31, 2017 2016 2015 Brokerage and Trading Revenue Gain (Loss) on Derivatives, Net Brokerage and Trading Revenue Gain (Loss) on Derivatives, Net Brokerage and Trading Revenue Gain (Loss) on Derivatives, Net Customer risk management programs: Interest rate contracts To-be-announced residential mortgage-backed securities $ 34,532 $ — $ 38,523 $ — $ 33,877 $ — Interest rate swaps 2,647 — 2,589 — 2,066 — Energy contracts 5,536 — 5,027 — 4,060 — Agricultural contracts 79 — 111 — 123 — Foreign exchange contracts 1,352 — 945 — 797 — Equity option contracts — — — — — — Total customer risk management programs 44,146 — 47,195 — 40,923 — Internal risk management programs 4,615 779 (4,592 ) (15,685 ) (209 ) 430 Total derivative contracts $ 48,761 $ 779 $ 42,603 $ (15,685 ) $ 40,714 $ 430 As discussed in Note 7 , certain derivative contracts not designated as hedging instruments related to mortgage loan commitments and forward sales contracts are included in Residential mortgage loans held for sale on the Consolidated Balance Sheets. See Note 7 for additional discussion of notional, fair value and impact on earnings of these contracts. No derivative contracts have been designated as hedging instruments for financial reporting purposes.

Loans and Allowances for Credit

Loans and Allowances for Credit Losses	12 Months Ended
	Dec. 31, 2017
Loans Receivable, Net [Abstract]
Loans [Text Block]	Loans and Allowances for Credit Losses The portfolio segments of the loan portfolio are as follows (in thousands): December 31, 2017 December 31, 2016 Fixed Rate Variable Rate Non-accrual Total Fixed Rate Variable Rate Non-accrual Total Commercial $ 2,217,432 $ 8,379,240 $ 137,303 $ 10,733,975 $ 2,327,085 $ 7,884,786 $ 178,953 $ 10,390,824 Commercial real estate 548,692 2,928,440 2,855 3,479,987 624,187 3,179,338 5,521 3,809,046 Residential mortgage 1,608,655 317,584 47,447 1,973,686 1,647,357 256,255 46,220 1,949,832 Personal 154,517 810,990 269 965,776 154,971 684,697 290 839,958 Total $ 4,529,296 $ 12,436,254 $ 187,874 $ 17,153,424 $ 4,753,600 $ 12,005,076 $ 230,984 $ 16,989,660 Accruing loans past due (90 days) 1 $ 633 $ 5 Foregone interest on nonaccrual loans $ 16,496 $ 15,990 1 Excludes residential mortgage loans guaranteed by agencies of the U.S. government. At December 31, 2017 , loans to businesses and individuals with collateral primarily located in Texas totaled $5.8 billion or 34% of the total loan portfolio. Loans to businesses and individuals with collateral primarily located in Oklahoma totaled $3.3 billion or 19% of our total loan portfolio. Loans for which the collateral location is not relevant, such as unsecured loans and reserve-based energy loans, are distributed by the borrower’s primary operating location. These geographic concentrations subject the loan portfolio to the general economic conditions within these areas. At December 31, 2016 , loans to businesses and individuals with collateral primarily located in Texas totaled $5.4 billion or 32% of the loan portfolio and loans to businesses and individuals with collateral primarily located in Oklahoma totaled $3.5 billion or 21% of the loan portfolio. Commercial Commercial loans represent loans for working capital, facilities acquisition or expansion, purchases of equipment and other needs of commercial customers primarily located within our geographical footprint. Commercial loans are underwritten individually and represent on-going relationships based on a thorough knowledge of the customer, the customer’s industry and market. While commercial loans are generally secured by the customer’s assets including real property, inventory, accounts receivable, operating equipment, interest in mineral rights and other property and may also include personal guarantees of the owners and related parties, the primary source of repayment of the loans is the on-going cash flow from operations of the customer’s business. Inherent lending risk is centrally monitored on a continuous basis from underwriting throughout the life of the loan for compliance with commercial lending policies. At December 31, 2017 , commercial loans with collateral primarily located in Texas totaled $3.6 billion or 34% of the commercial loan portfolio segment and commercial loans with collateral primarily located in Oklahoma totaled $2.0 billion or 18% of the commercial loan portfolio segment. The commercial loan portfolio segment is further divided into loan classes. The services loan class totaled $3.0 billion or 17% of total loans. Approximately $1.5 billion of loans in the services class consisted of loans with individual balances of less than $10 million . Businesses included in the services class include governmental, educational, commercial services, consumer services and utilities. The energy loan class totaled $2.9 billion or 17% of total loans, including $2.5 billion of outstanding loans to energy producers. Approximately 57% of committed production loans were secured by properties primarily producing oil and 43% are secured by properties producing natural gas. The healthcare loan class totaled $2.3 billion or 13% of total loans. The healthcare loan class consists primarily of loans for the development and operation of senior housing and care facilities, including independent living, assisted living and skilled nursing. Healthcare also includes loans to hospitals and other medical service providers. At December 31, 2016 , commercial loans with collateral primarily located in Texas totaled $3.3 billion or 32% of the commercial loan portfolio segment and commercial loans with collateral primarily located in Oklahoma totaled $2.1 billion or 21% of the commercial loan portfolio segment. The energy loan class totaled $2.5 billion or 15% of total loans, including $2.0 billion of outstanding loans to energy producers. At December 31, 2016 , approximately 57% of committed production loans were secured by properties primarily producing oil and 43% were secured by properties producing natural gas. The services loan class totaled $3.1 billion or 18% of total loans. Approximately $1.4 billion of loans in the services category consisted of loans with individual balances of less than $10 million . The healthcare loan class totaled $2.2 billion or 13% of total loans. Commercial Real Estate Commercial real estate loans are for the construction of buildings or other improvements to real estate and property held by borrowers for investment purposes primarily within our geographical footprint. We require collateral values in excess of the loan amounts, demonstrated cash flows in excess of expected debt service requirements, equity investment in the project and a portion of the project already sold, leased or permanent financing already secured. The expected cash flows from all significant new or renewed income producing property commitments are stress tested to reflect the risks in varying interest rates, vacancy rates and rental rates. As with commercial loans, inherent lending risks are centrally monitored on a continuous basis from underwriting throughout the life of the loan for compliance with applicable lending policies. At December 31, 2017 , 35% of commercial real estate loans are secured by properties primarily located in the Dallas and Houston areas of Texas. An additional 12% of commercial real estate loans are secured by properties located primarily in the Tulsa and Oklahoma City metropolitan areas of Oklahoma. At December 31, 2016 , 30% of commercial real estate loans were secured by properties in Texas, 11% of commercial real estate loans were secured by properties in Oklahoma. Residential Mortgage and Personal Residential mortgage loans provide funds for our customers to purchase or refinance their primary residence or to borrow against the equity in their home. Residential mortgage loans are secured by a first or second mortgage on the customer’s primary residence. Personal loans consist primarily of loans secured by the cash surrender value of insurance policies and marketable securities. It also includes direct loans secured by and for the purchase of automobiles, recreational and marine equipment as well as other unsecured loans. Residential mortgage and personal loans are made in accordance with underwriting policies. Credit scoring is assessed based on significant credit characteristics including credit history, residential and employment stability. Residential mortgage loans retained in the Company’s portfolio are primarily composed of various mortgage programs to support customer relationships including jumbo mortgage loans, non-builder construction loans and special loan programs for high net worth individuals and certain professionals. Jumbo loans may be fixed or variable rate and are fully amortizing. Jumbo loans generally conform to government sponsored entity standards, except that the loan size exceeds maximums required under these standards. These loans generally require a minimum FICO score of 720 and a maximum debt-to-income ratio (“DTI”) of 38% . Loan-to-value (“LTV”) ratios are tiered from 60% to 100% , depending on the market. Special mortgage programs include fixed and variable fully amortizing loans tailored to the needs of certain healthcare professionals. Variable rate loans are fully indexed at origination and may have fixed rates for three to ten years, then adjust annually thereafter. At December 31, 2017 and 2016 , residential mortgage loans included $198 million and $199 million , respectively, of loans guaranteed by U.S. government agencies previously sold into GNMA mortgage pools. These loans either have been repurchased or are eligible to be repurchased by the Company when certain defined delinquency criteria are met. Although payments on these loans generally are past due more than 90 days, interest continues to accrue based on the government guarantee. Home equity loans totaled $733 million at December 31, 2017 and $744 million at December 31, 2016 . At December 31, 2017 , 64% of the home equity loan portfolio was comprised of first lien loans and 36% of the home equity portfolio was comprised of junior lien loans. Junior lien loans were distributed 46% to amortizing term loans and 54% to revolving lines of credit. At December 31, 2016 , 65% of the home equity portfolio was comprised of first lien loans and 35% of the home equity loan portfolio was comprised of junior lien loans. Junior lien loans were distributed 52% to amortizing term loans and 48% to revolving lines of credit. Home equity loans generally require a minimum FICO score of 700 and a maximum DTI of 40%. The maximum loan amount available for our home equity loan products is generally $400 thousand . Revolving loans have a 5 year revolving period followed by 15 year term of amortizing repayments. Interest-only home equity loans may not be extended for any additional revolving time. All other home equity loans may be extended at management's discretion for an additional 5 year revolving term subject to an update of certain credit information. At December 31, 2017 , 31% of residential mortgage loans are secured by properties located in Oklahoma, 30% of residential mortgage loans are secured by properties located in Texas and 11% of residential mortgage are secured by properties located in Colorado. At December 31, 2016 , 33% of residential mortgage loans were secured by properties in Oklahoma, 29% of residential mortgage were secured by properties in Texas, 10% of residential mortgage loans are secured by properties in New Mexico and 10% of residential mortgage loans are secured by properties in Colorado. Credit Commitments Commitments to extend credit are agreements to lend to a customer as long as there is no violation of conditions established in the contract. Commitments generally have fixed expiration dates or other termination clauses and may require payment of a fee. At December 31, 2017 , outstanding commitments totaled $10.0 billion . Because some commitments are expected to expire before being drawn upon, the total commitment amounts do not necessarily represent future cash requirements. BOK Financial uses the same credit policies in making commitments as it does loans. The amount of collateral obtained, if deemed necessary, is based upon management’s credit evaluation of the borrower. Standby letters of credit are conditional commitments issued to guarantee the performance of a customer to a third party. Because the credit risk involved in issuing standby letters of credit is essentially the same as that involved in extending loan commitments, BOK Financial uses the same credit policies in evaluating the creditworthiness of the customer. Additionally, BOK Financial uses the same evaluation process in obtaining collateral on standby letters of credit as it does for loan commitments. The term of these standby letters of credit is defined in each commitment and typically corresponds with the underlying loan commitment. At December 31, 2017 , outstanding standby letters of credit totaled $648 million . Commercial letters of credit are used to facilitate customer trade transactions with the drafts being drawn when the underlying transaction is consummated. At December 31, 2017 , outstanding commercial letters of credit totaled $3.2 million . Allowances for Credit Losses BOK Financial maintains an allowance for loan losses and an accrual for off-balance sheet credit risk. The accrual for off-balance sheet credit risk is maintained at a level that is appropriate to cover estimated losses associated with credit instruments that are not currently recognized as assets such as loan commitments, standby letters of credit or guarantees. As discussed in greater detail in Note 7 , the Company also has separate accruals related to off-balance sheet credit risk related to residential mortgage loans previously sold with full or partial recourse and for residential mortgage loans sold to government sponsored agencies under standard representations and warranties. The allowance for loan losses consists of specific allowances attributed to impaired loans that have not yet been charged down to amounts we expect to recover, general allowances for unimpaired loans based on estimated loss rates by loan class and nonspecific allowances based on general economic conditions, concentration in loans with large balances and other relevant factors. The activity in the allowance for loan losses and the accrual for off-balance sheet credit risk related to loan commitments and standby letters of credit for the year ended December 31, 2017 is summarized as follows (in thousands): Commercial Commercial Real Estate Residential Mortgage Personal Nonspecific Allowance Total Allowance for loan losses: Beginning balance $ 140,213 $ 50,749 $ 18,224 $ 8,773 $ 28,200 $ 246,159 Provision for loan losses (595 ) 4,008 116 2,964 (5,983 ) 510 Loans charged off (19,810 ) (76 ) (649 ) (5,064 ) — (25,599 ) Recoveries 4,461 1,940 760 2,451 — 9,612 Ending balance $ 124,269 $ 56,621 $ 18,451 $ 9,124 $ 22,217 $ 230,682 Accrual for off-balance sheet credit risk: Beginning balance $ 11,063 $ 123 $ 50 $ 8 $ — $ 11,244 Provision for off-balance sheet credit risk (7,419 ) (78 ) (7 ) (6 ) — (7,510 ) Ending balance $ 3,644 $ 45 $ 43 $ 2 $ — $ 3,734 Total provision for credit losses $ (8,014 ) $ 3,930 $ 109 $ 2,958 $ (5,983 ) $ (7,000 ) The activity in the allowance for loan losses and the accrual for off-balance sheet credit risk related to loan commitments and standby letters of credit for the year ended December 31, 2016 is summarized as follows (in thousands): Commercial Commercial Real Estate Residential Mortgage Personal Nonspecific Allowance Total Allowance for loan losses: Beginning balance $ 130,334 $ 41,391 $ 19,509 $ 4,164 $ 30,126 $ 225,524 Provision for loan losses 43,980 8,075 (1,972 ) 7,310 (1,926 ) 55,467 Loans charged off (35,828 ) — (1,312 ) (5,448 ) — (42,588 ) Recoveries 1,727 1,283 1,999 2,747 — 7,756 Ending balance $ 140,213 $ 50,749 $ 18,224 $ 8,773 $ 28,200 $ 246,159 Accrual for off-balance sheet credit risk: Beginning balance $ 1,506 $ 153 $ 30 $ 22 $ — $ 1,711 Provision for off-balance sheet credit risk 9,557 (30 ) 20 (14 ) — 9,533 Ending balance $ 11,063 $ 123 $ 50 $ 8 $ — $ 11,244 Total provision for credit losses $ 53,537 $ 8,045 $ (1,952 ) $ 7,296 $ (1,926 ) $ 65,000 The activity in the allowance for loan losses and the accrual for off-balance sheet credit risk related to loan commitments and standby letters of credit for the year ended December 31, 2015 is summarized as follows (in thousands): Commercial Commercial Real Estate Residential Mortgage Personal Nonspecific Allowance Total Allowance for loan losses: Beginning balance $ 90,875 $ 42,445 $ 23,458 $ 4,233 $ 28,045 $ 189,056 Provision for loan losses 43,464 (11,189 ) (3,004 ) 2,167 2,081 33,519 Loans charged off (6,734 ) (944 ) (2,205 ) (5,288 ) — (15,171 ) Recoveries 2,729 11,079 1,260 3,052 — 18,120 Ending balance $ 130,334 $ 41,391 $ 19,509 $ 4,164 $ 30,126 $ 225,524 Accrual for off-balance sheet credit risk: Beginning balance $ 475 $ 707 $ 28 $ 20 $ — $ 1,230 Provision for off-balance sheet credit risk 1,031 (554 ) 2 2 — 481 Ending balance $ 1,506 $ 153 $ 30 $ 22 $ — $ 1,711 Total provision for credit losses $ 44,495 $ (11,743 ) $ (3,002 ) $ 2,169 $ 2,081 $ 34,000 The allowance for loan losses and recorded investment of the related loans by portfolio segment for each impairment measurement method at December 31, 2017 is as follows (in thousands): Collectively Measured for Impairment Individually Measured for Impairment Total Recorded Investment Related Allowance Recorded Investment Related Allowance Recorded Investment Related Allowance Commercial $ 10,596,672 $ 115,438 $ 137,303 $ 8,831 $ 10,733,975 $ 124,269 Commercial real estate 3,477,132 56,621 2,855 — 3,479,987 56,621 Residential mortgage 1,926,239 18,451 47,447 — 1,973,686 18,451 Personal 965,507 9,124 269 — 965,776 9,124 Total 16,965,550 199,634 187,874 8,831 17,153,424 208,465 Nonspecific allowance — — — — — 22,217 Total $ 16,965,550 $ 199,634 $ 187,874 $ 8,831 $ 17,153,424 $ 230,682 The allowance for loan losses and recorded investment of the related loans by portfolio segment for each impairment measurement method at December 31, 2016 is as follows (in thousands): Collectively Measured for Impairment Individually Measured for Impairment Total Recorded Investment Related Allowance Recorded Investment Related Allowance Recorded Investment Related Allowance Commercial $ 10,211,871 $ 139,416 $ 178,953 $ 797 $ 10,390,824 $ 140,213 Commercial real estate 3,803,525 50,749 5,521 — 3,809,046 50,749 Residential mortgage 1,903,612 18,178 46,220 46 1,949,832 18,224 Personal 839,668 8,773 290 — 839,958 8,773 Total 16,758,676 217,116 230,984 843 16,989,660 217,959 Nonspecific allowance — — — — — 28,200 Total $ 16,758,676 $ 217,116 $ 230,984 $ 843 $ 16,989,660 $ 246,159 Credit Quality Indicators The Company utilizes loan class and risk grading as primary credit quality indicators. Substantially all commercial and commercial real estate loans and certain residential mortgage and personal loans are risk graded based on a quarterly evaluation of the borrowers’ ability to repay the loans. Certain commercial loans and most residential mortgage and personal loans are small, homogeneous pools that are not risk graded. The allowance for loan losses and recorded investment of the related loans by portfolio segment for risk graded and non-risk graded loans at December 31, 2017 is as follows (in thousands): Internally Risk Graded Non-Graded Total Recorded Investment Related Allowance Recorded Investment Related Allowance Recorded Investment Related Allowance Commercial $ 10,706,035 $ 123,383 $ 27,940 $ 886 $ 10,733,975 $ 124,269 Commercial real estate 3,479,987 56,621 — — 3,479,987 56,621 Residential mortgage 234,477 2,947 1,739,209 15,504 1,973,686 18,451 Personal 877,390 6,461 88,386 2,663 965,776 9,124 Total 15,297,889 189,412 1,855,535 19,053 17,153,424 208,465 Nonspecific allowance — — — — — 22,217 Total $ 15,297,889 $ 189,412 $ 1,855,535 $ 19,053 $ 17,153,424 $ 230,682 The allowance for loan losses and recorded investment of the related loans by portfolio segment for risk graded and non-risk graded loans at December 31, 2016 is as follows (in thousands): Internally Risk Graded Non-Graded Total Recorded Investment Related Allowance Recorded Investment Related Allowance Recorded Investment Related Allowance Commercial $ 10,360,725 $ 139,293 $ 30,099 $ 920 $ 10,390,824 $ 140,213 Commercial real estate 3,809,046 50,749 — — 3,809,046 50,749 Residential mortgage 243,703 2,893 1,706,129 15,331 1,949,832 18,224 Personal 744,602 5,035 95,356 3,738 839,958 8,773 Total 15,158,076 197,970 1,831,584 19,989 16,989,660 217,959 Nonspecific allowance — — — — — 28,200 Total $ 15,158,076 $ 197,970 $ 1,831,584 $ 19,989 $ 16,989,660 $ 246,159 Loans are considered to be performing if they are in compliance with the original terms of the agreement which is consistent with the regulatory guideline of “pass.” Performing also includes loans considered to be “other loans especially mentioned” by regulatory guidelines and all residential mortgage loans guaranteed by agencies of the U.S. government that continue to accrue interest based on criteria of the guarantor's programs. Other loans especially mentioned are currently performing in compliance with the original terms of the agreement but may have a potential weakness that deserves management's close attention, consistent with regulatory guidelines. The risk grading process identified certain loans that have a well-defined weakness (e.g. inadequate debt service coverage or liquidity or marginal capitalization; repayment may depend on collateral or other risk mitigation) that may jeopardize liquidation of the debt and represent a greater risk due to deterioration in the financial condition of the borrower. This is consistent with the regulatory guideline for “substandard.” Because the borrowers are still performing in accordance with the original terms of the loan agreements, these loans were not placed in nonaccruing status. Nonaccruing loans represent loans for which full collection of principal and interest in accordance with the original terms of the loan agreements is uncertain. This is substantially the same criteria used to determine whether a loan is impaired and includes certain loans considered “substandard” and all loans considered “doubtful” by regulatory guidelines. The following table summarizes the Company’s loan portfolio at December 31, 2017 by the risk grade categories (in thousands): Internally Risk Graded Non-Graded Performing Pass Other Loans Especially Mentioned Accruing Substandard Nonaccrual Performing Nonaccrual Total Commercial: Energy $ 2,632,986 $ 60,288 $ 144,598 $ 92,284 $ — $ — $ 2,930,156 Services 2,943,869 13,927 26,533 2,620 — — 2,986,949 Wholesale/retail 1,443,917 19,263 5,502 2,574 — — 1,471,256 Manufacturing 472,869 6,653 11,290 5,962 — — 496,774 Healthcare 2,253,497 3,186 43,305 14,765 — — 2,314,753 Other commercial and industrial 478,951 7 8,161 19,028 27,870 70 534,087 Total commercial 10,226,089 103,324 239,389 137,233 27,870 70 10,733,975 Commercial real estate: Residential construction and land development 113,190 1,828 395 1,832 — — 117,245 Retail 686,915 4,243 98 276 — — 691,532 Office 824,408 7,087 — 275 — — 831,770 Multifamily 979,969 — 48 — — — 980,017 Industrial 573,014 — — — — — 573,014 Other commercial real estate 285,506 145 286 472 — — 286,409 Total commercial real estate 3,463,002 13,303 827 2,855 — — 3,479,987 Residential mortgage: Permanent mortgage 232,492 — 822 1,163 784,928 24,030 1,043,435 Permanent mortgages guaranteed by U.S. government agencies — — — — 188,327 9,179 197,506 Home equity — — — — 719,670 13,075 732,745 Total residential mortgage 232,492 — 822 1,163 1,692,925 46,284 1,973,686 Personal 875,696 1,548 63 83 88,200 186 965,776 Total $ 14,797,279 $ 118,175 $ 241,101 $ 141,334 $ 1,808,995 $ 46,540 $ 17,153,424 The following table summarizes the Company’s loan portfolio at December 31, 2016 by the risk grade categories (in thousands): Internally Risk Graded Non-Graded Performing Pass Other Loans Especially Mentioned Accruing Substandard Nonaccrual Performing Nonaccrual Total Commercial: Energy $ 1,937,790 $ 119,583 $ 307,996 132,499 $ — $ — $ 2,497,868 Services 3,052,002 10,960 37,855 8,173 — — 3,108,990 Wholesale/retail 1,535,463 16,886 13,062 11,407 — — 1,576,818 Manufacturing 468,314 26,532 15,198 4,931 — — 514,975 Healthcare 2,140,458 44,472 16,161 825 — — 2,201,916 Other commercial and industrial 433,789 5,309 — 21,060 30,041 58 490,257 Total commercial 9,567,816 223,742 390,272 178,895 30,041 58 10,390,824 Commercial real estate: Residential construction and land development 131,630 — 470 3,433 — — 135,533 Retail 756,418 4,745 399 326 — — 761,888 Office 798,462 — — 426 — — 798,888 Multifamily 898,800 — 4,434 38 — — 903,272 Industrial 871,673 — — 76 — — 871,749 Other commercial real estate 336,488 — 6 1,222 — — 337,716 Total commercial real estate 3,793,471 4,745 5,309 5,521 — — 3,809,046 Residential mortgage: Permanent mortgage 238,769 1,186 2,331 1,417 741,679 21,438 1,006,820 Permanent mortgages guaranteed by U.S. government agencies — — — — 187,541 11,846 199,387 Home equity — — — — 732,106 11,519 743,625 Total residential mortgage 238,769 1,186 2,331 1,417 1,661,326 44,803 1,949,832 Personal 743,451 — 1,054 97 95,163 193 839,958 Total $ 14,343,507 $ 229,673 $ 398,966 185,930 $ 1,786,530 $ 45,054 $ 16,989,660 Impaired Loans Loans are considered to be impaired when it is probable that the Company will not be able to collect all amounts due according to the contractual terms of the loan agreement. This includes all nonaccruing loans, all loans modified in a troubled debt restructuring and all loans repurchased from GNMA pools. A summary of impaired loans follows (in thousands): As of December 31, 2017 Year Ended Recorded Investment December 31, 2017 Unpaid Principal Balance Total With No With Allowance Related Allowance Average Recorded Interest Income Recognized Commercial: Energy $ 111,011 $ 92,284 $ 40,968 $ 51,316 $ 8,814 $ 112,392 $ — Services 5,324 2,620 2,620 — — 5,396 — Wholesale/retail 9,099 2,574 2,574 — — 6,990 — Manufacturing 6,073 5,962 5,962 — — 5,446 — Healthcare 25,140 14,765 14,765 — — 7,795 — Other commercial and industrial 27,957 19,098 19,080 18 17 20,108 — Total commercial 184,604 137,303 85,969 51,334 8,831 158,127 — Commercial real estate: Residential construction and land development 3,285 1,832 1,832 — — 2,633 — Retail 509 276 276 — — 301 — Office 287 275 275 — — 351 — Multifamily — — — — — 19 — Industrial — — — — — 38 — Other commercial real estate 670 472 472 — — 847 — Total commercial real estate 4,751 2,855 2,855 — — 4,189 — Residential mortgage: Permanent mortgage 30,435 25,193 25,193 — — 24,024 1,229 Permanent mortgage guaranteed by U.S. government agencies 1 203,814 197,506 197,506 — — 199,244 7,632 Home equity 14,548 13,075 13,075 — — 12,297 — Total residential mortgage 248,797 235,774 235,774 — — 235,565 8,861 Personal 307 269 269 — — 280 — Total $ 438,459 $ 376,201 $ 324,867 $ 51,334 $ 8,831 $ 398,161 $ 8,861 1 All permanent mortgage loans guaranteed by U.S. government agencies are considered impaired as we do not expect full collection of contractual principal and interest. At December 31, 2017 , $9.2 million of these loans are nonaccruing and $188 million are accruing based on the guarantee by U.S. government agencies. Generally, no interest income is recognized on impaired loans until all principal balances, including amounts charged-off, have been recovered. During 2017, we recognized $7.2 million as interest income on impaired loans that meet these conditions. As of December 31, 2016 Year Ended Recorded Investment December 31, 2016 Unpaid Principal Balance Total With No Allowance With Allowance Related Allowance Average Recorded Investment Interest Income Recognized Commercial: Energy $ 146,897 $ 132,499 $ 121,418 $ 11,081 $ 762 $ 80,100 $ — Services 11,723 8,173 8,173 — — 9,232 — Wholesale/retail 17,669 11,407 11,407 — — 7,163 — Manufacturing 5,320 4,931 4,931 — — 2,631 — Healthcare 1,147 825 825 — — 949 — Other commercial and industrial 29,006 21,118 21,083 35 35 10,870 — Total commercial 211,762 178,953 167,837 11,116 797 110,945 — Commercial real estate: Residential construction and land development 4,951 3,433 3,433 — — 3,921 — Retail 530 326 326 — — 823 — Office 521 426 426 — — 539 — Multifamily 1,000 38 38 — — 156 — Industrial 76 76 76 — — 76 — Other commercial real estate 7,349 1,222 1,222 — — 1,747 — Total commercial real estate 14,427 5,521 5,521 — — 7,262 — Residential mortgage: Permanent mortgage 28,830 22,855 22,809 46 46 25,920 1,255 Permanent mortgage guaranteed by U.S. government agencies 1 205,564 199,387 199,387 — — 193,889 7,759 Home equity 12,611 11,519 11,519 — — 10,937 — Total residential mortgage 247,005 233,761 233,715 46 46 230,746 9,014 Personal 332 290 290 — — 377 — Total $ 473,526 $ 418,525 $ 407,363 $ 11,162 $ 843 $ 349,330 $ 9,014 1 All permanent mortgage loans guaranteed by U.S. government agencies are considered impaired as we do not expect full collection of contractual principal and interest. At December 31, 2016 , $12 million of these loans are nonaccruing and $188 million are accruing based on the guarantee by U.S. government agencies. Troubled Debt Restructurings At December 31, 2017 the Company has $126 million in troubled debt restructurings (TDRs), of which $74 million are accruing residential mortgage loans guaranteed by U.S. government agencies. Approximately $48 million of TDRs are performing in accordance with the modified terms. The loans designated as TDRs had $117 thousand in charge offs during the year ended December 31, 2017 . At December 31, 2016 , TDRs totaled $147 million , of which $81 million were accruing residential mortgage loans guaranteed by U.S. government agencies. Approximately $75 million of TDRs were performing. The loans designated as TDRs had $4.7 million in charge offs during the year ended December 31, 2016 . TDRs generally consist of interest rate concessions, payment stream concessions or a combination of concessions to distressed borrowers. During the year ended December 31, 2017 , $57 million of loans were restructured. During the year ended December 31, 2016 , $52 million of loans were restructured. Nonaccrual & Past Due Loans Past due status for all loan classes is based on the actual number of days since the last payment was due according to the contractual terms of the loans. A summary of loans currently performing, loans past due and accruing and nonaccrual loans as of December 31, 2017 is as follows (in thousands): Past Due Current 30 to 59 Days 60 to 89 Days 90 Days or More Nonaccrual Total Commercial: Energy $ 2,833,668 $ — 4,204 $ — $ 92,284 $ 2,930,156 Services 2,983,222 514 486 107 2,620 2,986,949 Wholesale/retail 1,468,284 398 — — 2,574 1,471,256 Manufacturing 490,739 — 73 — 5,962 496,774 Healthcare 2,284,770 15,218 — — 14,765 2,314,753 Other commercial and industrial 514,701 85 78 125 19,098 534,087 Total commercial 10,575,384 16,215 4,841 232 137,303 10,733,975 Commercial real estate: Residential construction and land development 115,213 200 — — 1,832 117,245 Retail 691,256 — — — 276 691,532 Office 831,118 254 — 123 275 831,770 Multifamily 979,625 22 370 — — 980,017 Industrial 573,014 — — — — 573,014 Other commercial real estate 285,937 — — — 472 286,409 Total commercial real estate 3,476,163 476 370 123 2,855 3,479,987 Residential mortgage: Permanent mortgage 1,014,588 3,435 219 — 25,193 1,043,435 Permanent mortgages guaranteed by U.S. government agencies 22,692 18,978 13,468 133,189 9,179 197,506 Home equity 717,007 2,206 440 17 13,075 732,745 Total residential mortgage 1,754,287 24,619 14,127 133,206 47,447 1,973,686 Personal 964,374 681 191 261 269 965,776 Total $ 16,770,208 $ 41,991 19,529 $ 133,822 $ 187,874 $ 17,153,424 A summary of loans currently performing, loans past due and accruing and nonaccrual loans as of December 31, 2016 is as follows (in thousands): Past Due Current 30 to 59 Days 60 to 89 Days 90 Days or More Nonaccrual Total Commercial: Energy $ 2,364,890 $ 479 — $ — $ 132,499 $ 2,497,868 Services 3,099,605 191 1,021 — 8,173 3,108,990 Wholesale/retail 1,561,650 3,761 — — 11,407 1,576,818 Manufacturing 509,662 382 — — 4,931 514,975 Healthcare 2,201,050 — 41 — 825 2,201,916 Other commercial and industrial 468,981 155 3 — 21,118 490,257 Total commercial 10,205,838 4,968 1,065 — 178,953 10,390,824 Commercial real estate: Residential construction and land development 132,100 — — — 3,433 135,533 Retail 761,562 — — — 326 761,888 Office 798,462 — — — 426 798,888 Multifamily 903,234 — — — 38 903,272 Industrial 871,673 — — — 76 871,749 Other commercial real estate 336,488 6 — — 1,222 337,716 Total commercial real estate 3,803,519 6 — — 5,521 3,809,046 Residential mortgage: Permanent mortgage 979,386 3,299 1,280 — 22,855 1,006,820 Permanent mortgages guaranteed by U.S. government agencies 40,594 17,465 13,803 115,679 11,846 199,387 Home equity 729,493 2,276 337 — 11,519 743,625 Total residential mortgage 1,749,473 23,040 15,420 115,679 46,220 1,949,832 Personal 838,811 589 263 5 290 839,958 Total $ 16,597,641 $ 28,603 16,748 $ 115,684 $ 230,984 $ 16,989,660

Premises and Equipment

Premises and Equipment	12 Months Ended
	Dec. 31, 2017
Property, Plant and Equipment [Abstract]
Premises and Equipment Disclosure [Text Block]	Premises and Equipment Premises and equipment at December 31 are summarized as follows (in thousands): December 31, 2017 2016 Land $ 71,348 $ 70,552 Buildings and improvements 249,139 250,311 Software 188,826 158,155 Furniture and equipment 223,163 217,399 Construction in progress 23,348 36,743 Premises and equipment 755,824 733,160 Less accumulated depreciation 438,489 407,311 Premises and equipment, net of accumulated depreciation $ 317,335 $ 325,849 Depreciation expense of premises and equipment was $48 million , $40 million and $34 million for the years ended December 31, 2017 , 2016 and 2015 , respectively.

Goodwill and Intangible Assets

Goodwill and Intangible Assets	12 Months Ended
	Dec. 31, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill and Intangible Assets [Text Block]	Goodwill and Intangible Assets On December 1, 2016 , the Company acquired MBT Bancshares (“MBT”), parent company of Missouri Bank and Trust of Kansas City (“Mobank”) following regulatory approval of the transaction. Mobank operated four banking branches in the Kansas City, Mo. area. BOK Financial paid $102.5 million in an all-cash deal for all outstanding shares of MBT stock. MBT was merged into BOK Financial and Mobank became a wholly owned subsidiary of BOK Financial on December 1, 2016. On February 21, 2017, Mobank was merged with the Bank of Kansas City division of BOKF, NA. All branches in the Kansas City market operate under the Mobank name. The preliminary purchase price allocation was finalized during 2017, resulting in a $2.0 million increase in identifiable intangibles, $1.5 million decrease in premises and equipment and other repossessed assets, and a $526 thousand decrease in goodwill. The following table presents the original cost and accumulated amortization of intangible assets (in thousands): Dec. 31, 2017 2016 Core deposit premiums $ 6,510 $ 35,879 Less accumulated amortization 808 29,369 Net core deposit premiums 5,702 6,510 Other identifiable intangible assets 44,468 60,951 Less accumulated amortization 21,512 20,530 Net other identifiable intangible assets 22,956 40,421 Total intangible assets, net $ 28,658 $ 46,931 Expected amortization expense for intangible assets that will continue to be amortized (in thousands): Core Deposit Premiums Other Identifiable Intangible Assets Total 2018 $ 732 $ 4,322 $ 5,054 2019 716 3,970 4,686 2020 697 3,834 4,531 2021 675 3,477 4,152 2022 649 2,628 3,277 Thereafter 2,233 4,725 6,958 $ 5,702 $ 22,956 $ 28,658 The changes in the carrying value of goodwill by operating segment are as follows (in thousands): Commercial Banking Consumer Banking Wealth Management Funds Management and Other Total Balance, December 31, 2015 Goodwill $ 277,044 $ 39,251 $ 69,394 $ — $ 385,689 Accumulated impairment losses — (228 ) — — (228 ) 277,044 39,023 69,394 — 385,461 Goodwill recognized during 2016 1,210 — 2,126 66,160 69,496 Adjustment 2 $ (6,058 ) $ — $ — $ — (6,058 ) Balance, December 31, 2016 Goodwill 272,196 39,251 71,520 66,160 449,127 Accumulated impairment losses — (228 ) — — (228 ) 272,196 39,023 71,520 66,160 448,899 Goodwill recognized during 2017 4,301 — — — 4,301 Sales of consolidated merchant banking investments during 2017 (5,219 ) — (25 ) — (5,244 ) Adjustment 1 41,992 4,435 19,207 (66,160 ) (526 ) Balance, December 31, 2017 Goodwill 313,270 43,686 90,702 — 447,658 Accumulated impairment losses — (228 ) — — (228 ) $ 313,270 $ 43,458 $ 90,702 $ — $ 447,430 1 Goodwill from Mobank acquisition was not yet allocated to the segments as of December 31, 2016. Adjustment was made in 2017 for final purchase price adjustments and to allocate to the segments. 2 Completion of an external audit of Heartland Food Products resulted in a reallocation of the purchase price between net assets acquired, intangible assets and goodwill during 2016. The annual goodwill evaluations for 2017 and 2016 did not indicate impairment for any reporting unit. Economic conditions did not indicate that impairment existed for any identifiable intangible assets and therefore no impairment evaluation was performed.

Mortgage Banking Activities Mor

Mortgage Banking Activities Mortgage Banking Activities (Notes)	12 Months Ended
	Dec. 31, 2017
Mortgage Banking [Abstract]
Mortgage Banking Activities [Text Block]	Mortgage Banking Activities Residential Mortgage Loan Production The Company originates, markets and services conventional and government-sponsored residential mortgage loans. Generally, conforming fixed rate residential mortgage loans are held for sale in the secondary market and non-conforming and adjustable-rate residential mortgage loans are held for investment. The volume of mortgage loans originated for sale and secondary market prices are the primary drivers of originating and marketing revenue. Residential mortgage loan commitments are generally outstanding for 60 to 90 days, which represents the typical period from commitment to originate a residential mortgage loan to when the closed loan is sold to an investor. Residential mortgage loan commitments are subject to both credit and interest rate risk. Credit risk is managed through underwriting policies and procedures, including collateral requirements, which are generally accepted by the secondary loan markets. Exposure to interest rate fluctuations is partially managed through forward sales of residential mortgage-backed securities and forward sales contracts. These latter contracts set the price for loans that will be delivered in the next 60 to 90 days. The unpaid principal balance of residential mortgage loans held for sale, notional amounts of derivative contracts related to residential mortgage loan commitments and forward contract sales and their related fair values included in Mortgage loans held for sale on the Consolidated Balance Sheets were (in thousands): December 31, 2017 December 31, 2016 Unpaid Principal Balance/ Notional Fair Value Unpaid Principal Balance/ Notional Fair Value Residential mortgage loans held for sale $ 212,525 $ 215,113 $ 286,414 $ 286,971 Residential mortgage loan commitments 222,919 6,523 318,359 9,733 Forward sales contracts 380,159 (258 ) 569,543 5,193 $ 221,378 $ 301,897 No residential mortgage loans held for sale were 90 days or more past due or considered impaired as of December 31, 2017 or December 31, 2016 . No credit losses were recognized on residential mortgage loans held for sale for the years ended December 31, 2017 , 2016 and 2015 . Mortgage banking revenue was as follows (in thousands): Year Ended 2017 2016 2015 Production revenue: Net realized gains on sales of mortgage loans $ 45,128 $ 68,947 $ 67,407 Net change in unrealized gain on mortgage loans held for sale 2,031 (5,311 ) (784 ) Net change in the fair value of mortgage loan commitments (3,210 ) 1,599 (1,837 ) Net change in the fair value of forward sales contracts (5,451 ) 4,393 4,801 Total mortgage production revenue 38,498 69,628 69,587 Servicing revenue 66,221 64,286 56,415 Total mortgage banking revenue $ 104,719 $ 133,914 $ 126,002 Mortgage production revenue includes gain (loss) on residential mortgage loans held for sale and changes in the fair value of derivative contracts not designated as hedging instruments related to residential mortgage loan commitments and forward sales contracts. Servicing revenue includes servicing fee income and late charges on loans serviced for others. Residential Mortgage Servicing The Company generally retains the right to service residential mortgage loans sold and may purchase mortgage servicing rights. The unpaid principal balance of loans serviced for others is the primary driver of servicing revenue. The following represents a summary of mortgage servicing rights (Dollars in thousands): December 31, 2017 2016 2015 Number of residential mortgage loans serviced for others 136,528 139,340 131,859 Outstanding principal balance of residential mortgage loans serviced for others $ 22,046,632 $ 21,997,568 $ 19,678,226 Weighted average interest rate 3.94 % 3.97 % 4.12 % Remaining contractual term (in months) 297 301 300 Activity in capitalized mortgage servicing rights during the three years ended December 31, 2017 is as follows (in thousands): Balance, December 31, 2014 $ 171,976 Additions, net 79,546 Change in fair value due to loan runoff (28,064 ) Change in fair value due to market changes (4,853 ) Balance, December 31, 2015 218,605 Additions, net 71,405 Change in fair value due to loan runoff (40,744 ) Change in fair value due to market changes (2,193 ) Balance, December 31, 2016 247,073 Additions, net 39,149 Change in fair value due to loan runoff (33,527 ) Change in fair value due to market changes 172 Balance, December 31, 2017 $ 252,867 Changes in the fair value of mortgage servicing rights due to market changes are included in Other operating revenue in the Consolidated Statements of Earnings. Changes in fair value due to loan runoff are included in Mortgage banking costs. Mortgage servicing rights are not traded in active markets. Fair value is determined by discounting the projected net cash flows. Significant assumptions used to determine fair value considered to be significant unobservable inputs were as follows: December 31, 2017 2016 Discount rate – risk-free rate plus a market premium 9.84% 10.08% Prepayment rate - based upon loan interest rate, original term and loan type 8.72%-15.16% 8.98%-16.91% Loan servicing costs – annually per loan based upon loan type: Performing loans $65 - $88 $63 - $120 Delinquent loans $150 - $500 $150 - $500 Loans in foreclosure $1,000 - $4,000 $650 - $4,250 Primary/secondary mortgage rate spread 105 bps 105 bps Escrow earnings rate – indexed to rates paid on deposit accounts with comparable average life 2.24% 1.98% Changes in primary residential mortgage interest rates directly affect the prepayment speeds used in valuing our mortgage servicing rights. A separate third party model is used to estimate prepayment speeds based on interest rates, housing turnover rates, estimated loan curtailment, anticipated defaults and other relevant factors. The prepayment model is updated periodically for changes in market conditions and adjusted to better correlate with actual performance of BOK Financial’s servicing portfolio. The aging status of our mortgage loans serviced for others by investor at December 31, 2017 follows (in thousands): Past Due Current 30 to 59 Days 60 to 89 Days 90 Days or More Total FHLMC $ 7,995,369 $ 81,805 $ 14,091 $ 32,756 $ 8,124,021 FNMA 6,595,410 81,405 13,856 27,083 6,717,754 GNMA 6,431,808 232,937 60,556 19,743 6,745,044 Other 452,227 4,271 1,128 2,187 459,813 Total $ 21,474,814 $ 400,418 $ 89,631 $ 81,769 $ 22,046,632

Deposits

Deposits	12 Months Ended
	Dec. 31, 2017
Deposits [Abstract]
Deposits [Text Block]	Deposits Interest expense on deposits is summarized as follows (in thousands): Year Ended December 31, 2017 2016 2015 Transaction deposits $ 28,627 $ 13,906 $ 8,821 Savings 359 386 383 Time: Certificates of deposits under $100,000 7,702 8,776 11,894 Certificates of deposits $100,000 and over 12,393 10,123 10,643 Other time deposits 4,722 7,303 12,429 Total time 24,817 26,202 34,966 Total $ 53,803 $ 40,494 $ 44,170 The aggregate amounts of time deposits in denominations of $250,000 or more at December 31, 2017 and 2016 were $ 797 million and $ 866 million , respectively. Time deposit maturities are as follows: 2018 – $ 1.2 billion , 2019 – $ 221 million , 2020 – $ 86 million , 2021 – $ 102 million , 2022 – $ 132 million and $ 307 million thereafter. The aggregate amount of overdrawn customer transaction deposits that have been reclassified as loan balances was $ 5.9 million at December 31, 2017 and $ 9.7 million at December 31, 2016 .

Other Borrowings

Other Borrowings	12 Months Ended
	Dec. 31, 2017
Debt Disclosure [Abstract]
Other borrowings [Text Block]	Other Borrowings Information relating to other borrowings is summarized as follows (dollars in thousands): As of Year Ended December 31, 2017 December 31, 2017 Balance Rate Average Balance Rate Maximum Parent company and other non-bank subsidiaries: Trust preferred debt $ — — % $ 3,296 3.52 % $ 7,217 Other — — % 935 11.11 % 3,104 Total other borrowings — 4,231 7.00 % Subordinated debentures 144,677 5.60 % 144,658 5.62 % $ 144,677 Total parent company and other non-bank subsidiaries 144,677 148,889 5.65 % BOKF, NA: Funds purchased 58,628 1.00 % 58,064 0.73 % 80,967 Repurchase agreements 516,335 0.17 % 433,791 0.10 % 536,094 Other borrowings: Federal Home Loan Bank advances 5,100,000 1.47 % 5,882,466 1.13 % 6,200,000 GNMA repurchase liability 19,947 4.22 % 20,509 4.59 % 24,139 Other 14,950 2.61 % 15,382 2.38 % 15,506 Total other borrowings 5,134,897 5,918,357 1.14 % Subordinated debentures — — % — — % — Total BOKF, NA 5,709,860 6,410,212 1.07 % Total other borrowed funds $ 5,854,537 $ 6,559,101 1.18 % As of Year Ended December 31, 2016 December 31, 2016 Balance Rate Average Balance Rate Maximum Parent company and other non-bank subsidiaries: Trust preferred debt $ 7,217 3.28 % $ 611 3.27 % $ 7,217 Other 1,092 8.27 % 2,073 16.11 % 3,157 Total other borrowings 8,309 2,684 13.19 % Subordinated debentures 144,640 5.60 % 74,428 5.59 % 145,393 Total parent company and other non-bank subsidiaries 152,949 77,112 5.86 % BOKF, NA: Funds purchased 57,929 0.38 % 78,222 0.24 % 567,103 Repurchase agreements 668,661 0.02 % 589,145 0.04 % 668,661 Other borrowings: Federal Home Loan Bank advances 4,800,000 0.72 % 5,985,656 0.55 % 6,500,000 GNMA repurchase liability 22,471 4.26 % 15,637 4.74 % 22,471 Other 15,292 2.66 % 15,670 2.41 % 15,797 Total other borrowings 4,837,763 6,016,963 0.57 % Subordinated debentures — — % 140,414 1.35 % 226,434 Total BOKF, NA 5,564,353 6,824,744 0.54 % Total other borrowed funds $ 5,717,302 $ 6,901,856 0.60 % As of Year Ended December 31, 2015 December 31, 2015 Balance Rate Average Balance Rate Maximum Parent company and other non-bank subsidiaries: Trust preferred debt $ — — % $ — — % $ — Other — — % — — % — Total other borrowings — — — % Subordinated debentures — — % — — % — Total parent company and other non-bank subsidiaries — — — % BOKF, NA: Funds purchased 491,192 0.15 % 73,219 0.09 % 491,192 Repurchase agreements 722,444 0.02 % 623,921 0.04 % 1,008,144 Other borrowings: Federal Home Loan Bank advances 4,800,000 0.48 % 4,921,739 0.28 % 5,000,000 GNMA repurchase liability 19,478 4.75 % 16,668 4.95 % 19,478 Other 18,402 2.70 % 18,768 2.35 % 26,058 Total other borrowings 4,837,880 4,957,175 0.33 % Subordinated debentures 226,350 1.05 % 226,332 1.84 % 348,076 Total BOKF, NA 6,277,866 5,880,647 0.36 % Total other borrowed funds $ 6,277,866 $ 5,880,647 0.36 % Aggregate annual principal repayments at December 31, 2017 are as follows (in thousands): Parent Company and Other Non-bank Subsidiaries BOKF, NA 2018 $ — $ 5,695,621 2019 — 956 2020 — 961 2021 — 965 2022 — 970 Thereafter 144,677 10,387 Total $ 144,677 $ 5,709,860 Funds purchased are unsecured and generally mature within one to ninety days from the transaction date. Securities repurchase agreements are recorded as secured borrowings that generally mature within ninety days and are secured by certain available for sale securities. Additional information relating to securities sold under agreements to repurchase and related liabilities at December 31, 2017 and 2016 is as follows (dollars in thousands): December 31, 2017 Amortized Fair Repurchase Average Security Sold/Maturity Cost Value Liability 1 Rate U.S. government agency mortgage-backed securities: Overnight 1 $ 525,452 $ 523,914 $ 516,335 0.17 % Long-term — — — — % Total Agency Securities $ 525,452 $ 523,914 $ 516,335 0.17 % December 31, 2016 Amortized Fair Repurchase Average Security Sold/Maturity Cost Value Liability 1 Rate U.S. government agency mortgage-backed securities: Overnight 1 $ 655,529 $ 655,851 $ 668,661 0.02 % Long-term — — — — % Total Agency Securities $ 655,529 $ 655,851 $ 668,661 0.02 % 1 BOK Financial maintains control over the securities underlying overnight repurchase agreements and generally transfers control over securities underlying longer-term dealer repurchase agreements to the respective counterparty. Borrowings from the Federal Home Loan Banks are used for funding purposes. In accordance with policies of the Federal Home Loan Banks, BOK Financial has granted a blanket pledge of eligible assets (generally unencumbered U.S. Treasury and residential mortgage-backed securities, 1-4 family loans and multifamily loans) as collateral for these advances. The Federal Home Loan Banks have issued letters of credit totaling $272 million to secure BOK Financial’s obligations to depositors of public funds. The unused credit available to BOK Financial at December 31, 2017 pursuant to the Federal Home Loan Bank’s collateral policies is $1.2 billion . In 2016, BOK Financial issued $150 million of subordinated debt that will mature on June 30, 2056 . Interest on this debt bears an interest rate of 5.375% , payable quarterly. On June 30, 2021 , BOK Financial will have the option to redeem the debt at the principal amount plus accrued interest, subject to regulatory approval. In conjunction with the acquisition of MBT, BOK Financial assumed $7.2 million of variable rate subordinated trust preferred debt. Interest was payable quarterly at three-month LIBOR plus 2.95% on $3.1 million and three-month LIBOR plus 1.82% on $4.1 million . This trust preferred debt was redeemed during 2017. BOK Financial Securities, Inc. may borrow funds from Pershing, LLC ("Pershing"), a clearing broker/dealer and a wholly owned subsidiary of Bank of New York Mellon, for the purposes of financing securities purchases or to facilitate funding of investment banking activities, on terms to be negotiated at the time of the borrowing. BOK Financial Securities, Inc. had no borrowings from Pershing outstanding at December 31, 2017 or December 31, 2016 . In 2007, BOKF, NA issued $250 million of subordinated debt due May 15, 2017 . Interest on this debt was based upon a fixed rate of 5.75% through May 14, 2012 and is based on a floating rate of three-month LIBOR plus 0.69% thereafter . The proceeds of this debt were used to fund the Worth National Bank and First United Bank acquisitions and to fund continued asset growth. The outstanding balance of this subordinated debt was $226 million at December 31, 2015. The remaining outstanding balance was called during 2016. The Company has a liability related to the repurchase of certain delinquent residential mortgage loans previously sold into GNMA mortgage pools. Interest is payable at rates contractually due to investors.

Federal and State Income Taxes

Federal and State Income Taxes	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Federal and State Income Taxes [Text Block]	Federal and State Income Taxes The Tax Cuts and Jobs Act (the "Act"), which was enacted on December 22, 2017, reduces the federal corporate tax rate from 35% to 21% for periods beginning January 1, 2018. Provisions of the Act are broad and complex. As result, we are still evaluating the impact that certain aspects of the Act will have on the Company's financial position and results of operations, including recognition and measurement of deferred tax assets and liabilities and the determination of effective current and deferred federal and state income tax rates. We have made reasonable estimates of the Act's impact on net deferred tax assets and recorded a provisional adjustment of $9.5 million , including $6.4 million of net deferred tax assets resulting from temporary differences recognized in Accumulated other comprehensive income on the Company's balance sheets. Additionally, we recognized a provisional adjustment of $2.2 million for deferred taxes resulting from executive compensation that may no longer be deductible. We are not aware of any material areas where we were not able to determine provisional amounts. However, accounting for income tax effects of the Act is still in process and provisional adjustments recognized in 2017 may be adjusted as a result of our on-going evaluation, including subsequent guidance provided by federal and state taxing authorities and other information as it becomes available. Deferred income taxes reflect the net tax effects of temporary differences between the carrying amounts of assets and liabilities for financial reporting purposes and the amounts used for income tax purposes. As a result of the Act, deferred tax balances at December 31, 2017 generally have been revalued from the previous combined federal and state statutory rate of 38.9% to 25.5% . Significant components of deferred tax assets and liabilities are as follows (in thousands): December 31, 2017 2016 Deferred tax assets: Available for sale securities mark to market $ 12,083 $ 5,779 Share-based compensation 7,598 9,360 Credit loss allowances 58,666 99,191 Valuation adjustments 8,102 12,222 Deferred compensation 12,215 30,262 Unearned fees 9,265 11,877 Other 30,859 42,541 Total deferred tax assets 138,788 211,232 Deferred tax liabilities: Depreciation 15,817 25,877 Mortgage servicing rights 63,112 92,748 Lease financing 9,973 17,923 Other 34,880 45,363 Total deferred tax liabilities 123,782 181,911 Net deferred tax assets $ 15,006 $ 29,321 No valuation allowance was necessary on deferred tax assets as of December 31, 2017 and 2016 . The significant components of the provision for income taxes attributable to continuing operations for BOK Financial are shown below (in thousands): Year Ended December 31, 2017 2016 2015 Current income tax expense: Federal $ 141,607 $ 107,379 $ 117,566 State 14,592 11,028 12,397 Total current income tax expense 156,199 118,407 129,963 Deferred income tax expense: Federal 25,525 (11,340 ) 8,397 State 869 (690 ) 1,024 Total deferred income tax expense 26,394 (12,030 ) 9,421 Total income tax expense $ 182,593 $ 106,377 $ 139,384 The reconciliations of income attributable to continuing operations at the U.S. federal statutory tax rate to income tax expense are as follows (in thousands): Year Ended December 31, 2017 2016 2015 Amount: Federal statutory tax $ 181,397 $ 118,530 $ 151,075 Tax exempt revenue (12,402 ) (10,544 ) (9,553 ) Effect of state income taxes, net of federal benefit 10,701 6,478 9,082 Utilization of tax credits: Low-income housing tax credits, net of amortization (5,356 ) (4,171 ) (3,874 ) Other tax credits (1,455 ) (2,085 ) (2,085 ) Bank-owned life insurance (3,121 ) (2,911 ) (3,264 ) Share-based compensation (2,817 ) — — Revaluation of net deferred tax assets due to change in federal tax rates 9,456 — — Write-off of deferred tax assets related to executive compensation 2,216 — — Other, net 3,974 1,080 (1,997 ) Total income tax expense $ 182,593 $ 106,377 $ 139,384 Year Ended December 31, 2017 2016 2015 Percent of pretax income: Federal statutory tax 35.0 % 35.0 % 35.0 % Tax exempt revenue (2.4 ) (3.1 ) (2.2 ) Effect of state income taxes, net of federal benefit 2.0 1.9 2.1 Utilization of tax credits: Low-income housing tax credits, net of amortization (1.0 ) (1.2 ) (0.9 ) Other tax credits (0.3 ) (0.6 ) (0.5 ) Bank-owned life insurance (0.6 ) (0.9 ) (0.7 ) Share-based compensation (0.5 ) — — Revaluation of net deferred tax assets due to change in federal tax rates 1.8 — — Write-off of deferred tax assets related to executive compensation 0.4 — — Other, net 0.8 0.3 (0.5 ) Total 35.2 % 31.4 % 32.3 % A reconciliation of the beginning and ending amount of unrecognized tax benefits is as follows (in thousands): 2017 2016 2015 Balance as of January 1 $ 15,841 $ 13,232 $ 13,374 Additions for tax for current year positions 4,645 5,640 2,226 Settlements during the period — — — Lapses of applicable statute of limitations (2,376 ) (3,031 ) (2,368 ) Balance as of December 31 $ 18,110 $ 15,841 $ 13,232 Of the above unrecognized tax benefits, $12.2 million , if recognized, would have affected the effective tax rate. BOK Financial recognizes interest and penalties accrued related to unrecognized tax benefits in income tax expense. The Company recognized $1.2 million for 2017 , $1.0 million for 2016 and $1.0 million for 2015 in interest and penalties. The Company had approximately $4.0 million and $3.5 million accrued for the payment of interest and penalties at December 31, 2017 and 2016 , respectively. Federal statutes remain open for federal tax returns filed in the previous three reporting periods. Various state income tax statutes remain open for the previous three to six reporting periods.

Employee Benefits

Employee Benefits	12 Months Ended
	Dec. 31, 2017
Retirement Benefits [Abstract]
Employee Benefits [Text Block]	Employee Benefits BOK Financial sponsors a defined benefit cash balance Pension Plan for all employees who satisfy certain age and service requirements. Pension Plan benefits were curtailed as of April 1, 2006. No participants may be added to the plan and no additional service benefits will be accrued. During 2017 and 2016, interest accrued on employees' account balances at a variable rate tied to the five-year trailing average of five-year U.S. Treasury securities plus 1.5% . The rate has a floor of 3.0% and a ceiling of 5.0% . The 2017 quarterly variable rates remained at 3.00% . The following table presents information regarding this plan (in thousands): December 31, 2017 2016 Change in projected benefit obligation: Projected benefit obligation at beginning of year $ 34,964 $ 38,797 Interest cost 1,153 1,309 Actuarial loss (gain) 223 (55 ) Benefits paid (5,443 ) (5,087 ) Projected benefit obligation at end of year 1,2 $ 30,897 $ 34,964 Change in plan assets: Plan assets at fair value at beginning of year $ 41,769 $ 44,190 Actual return on plan assets 4,093 2,666 Benefits paid (5,443 ) (5,087 ) Plan assets at fair value at end of year $ 40,419 $ 41,769 Funded status of the plan $ 9,522 $ 6,805 Components of net periodic benefit: Interest cost $ 1,153 $ 1,309 Expected return on plan assets (2,041 ) (2,167 ) Other 184 (741 ) Net periodic benefit cost (credit) $ (704 ) $ (1,599 ) 1 Projected benefit obligation equals accumulated benefit obligation. 2 Projected benefit obligation is based on January 1 measurement date. Weighted-average assumptions as of December 31: 2017 2016 Discount rate 3.30 % 3.43 % Expected return on plan assets 5.50 % 5.00 % As of December 31, 2017 , expected future benefit payments related to the Pension Plan were as follows (in thousands): 2018 $ 2,831 2019 2,889 2020 2,763 2021 2,769 2022 2,813 Thereafter 25,501 Total estimated future benefit payments $ 39,566 Assets of the Pension Plan consist primarily of shares in the Cavanal Hill Active Core Fund. The stated objective of this fund is to provide an attractive total return with a well-balanced mix of equities and bonds. The typical portfolio mix is approximately 60% equities and 40% bonds. The net asset value of shares in the Cavanal Hill Funds is reported daily based on market quotations for the Fund’s securities. Management considers the Fund's recent and long-term performance as indicators when setting the expected return on plan assets. The maximum tax deductible Pension Plan contribution for 2017 was $10 million . No minimum contribution was required for 2017 , 2016 or 2015 . Employee contributions to the Thrift Plan are eligible for Company matching equal to 6% of base compensation, as defined in the plan. The Company-provided matching contribution rates range from 50% for employees with less than 4 years of service to 200% for employees with 15 or more years of service. Additionally, a maximum Company-provided, non-elective annual contribution of up to $750 per participant is provided for employees whose annual base compensation is less than $40,000 . Participants may direct investments in their accounts to a variety of options, including a BOK Financial common stock fund and Cavanal Hill funds. Employer contributions, which are invested in accordance with the participant’s investment options, vest over five years. Thrift Plan expenses were $22.8 million for 2017 , $22.4 million for 2016 and $20.6 million for 2015 .

Share-Based Compensation Plans

Share-Based Compensation Plans	12 Months Ended
	Dec. 31, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Share-Based Compensation Plans [Text Block]	Share-Based Compensation Plans The shareholders and Board of Directors of BOK Financial have approved various share-based compensation plans. An independent compensation committee of the Board of Directors determines the number of awards granted to the Chief Executive Officer and other senior executives. Share-based compensation is granted to other officers and employees as determined by the Chief Executive Officer. The following table presents stock options outstanding during 2017 , 2016 and 2015 under these plans (in thousands, except for per share data): Number Weighted- Average Exercise Price Aggregate Intrinsic Value Options outstanding at December 31, 2014 793,891 $ 49.05 $ 8,725 Options awarded — — Options exercised (286,678 ) 47.86 Options forfeited (22,304 ) 48.90 Options expired (4,874 ) 51.32 Options outstanding at December 31, 2015 480,035 49.75 4,821 Options awarded — — Options exercised (249,404 ) 47.60 Options forfeited (4,098 ) 55.44 Options expired (8,009 ) 53.43 Options outstanding at December 31, 2016 218,524 51.95 6,793 Options awarded — — Options exercised (99,556 ) 50.35 Options forfeited (624 ) 54.95 Options expired (793 ) 48.75 Options outstanding at December 31, 2017 117,551 $ 53.26 $ 4,592 Options vested at: December 31, 2015 243,395 $ 48.17 $ 2,829 December 31, 2016 93,117 46.22 3,429 December 31, 2017 51,286 48.62 2,241 At December 31, 2017 , the weighted average remaining contractual life of options outstanding was 2.54 years and the weighted average remaining contractual life of vested options was 1.16 years . The aggregate intrinsic value of options exercised was $ 3.5 million for 2017 , $ 6.2 million for 2016 and $ 5.1 million for 2015 . The following represents a summary of the non-vested stock awards as of December 31, 2017 (in thousands): Shares Weighted Average Grant Date Fair Value Non-vested at January 1, 2015 688,611 Granted 312,755 $57.66 Vested (114,045 ) $50.15 Forfeited (96,212 ) $58.33 Non-vested at December 31, 2015 791,109 Granted 256,670 $55.35 Vested (213,941 ) $55.87 Forfeited (47,132 ) $57.86 Non-vested at December 31, 2016 786,706 Granted 177,807 $86.95 Vested (194,419 ) $63.07 Forfeited (102,991 ) $78.70 Non-vested at December 31, 2017 667,103 Compensation expense recognized on non-vested shares totaled $23.2 million for 2017 , $10.2 million for 2016 and $12.0 million for 2015 . Unrecognized compensation cost of non-vested shares totaled $ 15.8 million at December 31, 2017 . We expect to recognize compensation expense of $ 9.9 million in 2018 , $ 5.9 million in 2019 , and $ 82 thousand in 2020 . Compensation cost for 296,518 non-vested shares is variable based on the current fair value of BOK Financial common shares. All non-vested shares are subject to forfeiture for failure to meet service requirements and 297,567 non-vested shares may be increased or decreased based on performance criteria defined in the plan documents. During January 2018, BOK Financial awarded 150,419 shares of non-vested stock with a fair value per award of $94.77 . The aggregate compensation cost of these awards totaled approximately $ 14.3 million .

Related Parties

Related Parties	12 Months Ended
	Dec. 31, 2017
Related Party Transactions [Abstract]
Related Parties [Text Block]	Related Parties In compliance with applicable banking regulations, the Company may extend credit to certain executive officers, directors, principal shareholders and their affiliates (collectively referred to as “related parties”) in the ordinary course of business. The Company’s loans to related parties do not involve more than the normal credit risk and there are no nonaccruing or impaired related party loans outstanding at December 31, 2017 or 2016 . Activity in loans to related parties is summarized as follows (in thousands): Year Ended December 31, 2017 2016 Beginning balance $ 136,945 $ 594,225 Advances 1,559,291 884,511 Payments (1,585,865 ) (1,123,747 ) Adjustments 1 (125 ) (218,044 ) Ending balance $ 110,246 $ 136,945 1 Adjustments generally consist of changes in status as a related party. As defined by banking regulations, loan commitments and equity investments to a single affiliate may not exceed 10% of unimpaired capital and surplus while loan commitments and equity investments to all affiliates may not exceed 20% of unimpaired capital and surplus. All loans to affiliates must be fully secured by eligible collateral. At December 31, 2017 , loan commitments and equity investments were limited to $310 million to a single affiliate and $620 million to all affiliates. The largest loan commitment and equity investment to a single affiliate was $223 million and the aggregate loan commitments and equity investments to all affiliates were $323 million . The largest outstanding amount to a single affiliate at December 31, 2017 was $12 million and the total outstanding amounts to all affiliates were $16 million . At December 31, 2016 , total loan commitments and equity investments to all affiliates were $337 million and the total outstanding amounts to all affiliates were $39 million . Certain related parties are customers of the Company for services other than loans, including consumer banking, corporate banking, risk management, wealth management, brokerage and trading, or fiduciary/trust services. The Company engages in transactions with related parties in the ordinary course of business in compliance with applicable regulations. The Company rents office space in facilities owned by affiliates of Mr. Kaiser, its Chairman and principal shareholder. Lease payments totaled $1.0 million for 2017, $1.1 million for 2016 and $975 thousand for 2015. During 2017, the Company also invested $580 thousand in QRC Valve Distributors, which is indirectly owned by Mr. Kaiser. QuikTrip Corporation has entered into a fee sharing agreement with TransFund, BOKF’s electronic funds transfer network (“TransFund”), respecting transactions completed at TransFund automated teller machines placed in QuikTrip locations. In 2017, BOKF paid QuikTrip approximately $8.3 million pursuant to this agreement. During 2017, the Company sold $1.2 million of Oklahoma state income tax credits to QuikTrip Corporation. Mr. Cadieux, a BOK Financial director, is Chief Executive Officer, Chairman, and a significant shareholder of QuikTrip Corporation. Cavanal Hill Investment Management, Inc., a wholly-owned subsidiary of BOKF, NA, is the administrator to and investment advisor for the Cavanal Hill Funds (the "Funds"), a diversified, open-ended investment company established as a business trust under the Investment Company Act of 1940 (the "1940 Act"). BOKF, NA is custodian and Cavanal Hill Distributors, Inc. is distributor for the Funds. The Funds’ products are offered to customers, employee benefit plans, trusts and the general public in the ordinary course of business. Approximately 93% of the Funds’ assets of $ 3.7 billion are held for the Company's clients. A Company executive officer serves on the Funds' board of trustees and officers of BOKF, NA serve as president and secretary of the Funds. A majority of the members of the Funds’ board of trustees are, however, independent of the Company and the Funds are managed by its board of trustees.

Commitments and Contingent Liab

Commitments and Contingent Liabilities	12 Months Ended
	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingent Liabilities [Text Block]	Commitments and Contingent Liabilities Litigation Contingencies As a member of Visa, BOK Financial is obligated for a proportionate share of certain covered litigation losses incurred by Visa under a retrospective responsibility plan. A contingent liability was recognized for the Company’s share of Visa’s covered litigation liabilities. Visa funded an escrow account to cover litigation claims, including covered litigation losses under the retrospective responsibility plan, with proceeds from its initial public offering in 2008 and from available cash. BOK Financial currently owns 252,233 Visa Class B shares which are convertible into 415,755 shares of Visa Class A shares after the final settlement of all covered litigation. Class B shares may be diluted in the future if the escrow fund is not adequate to cover future covered litigation costs. Therefore, no value has been currently assigned to the Class B shares and no value may be assigned until the Class B shares are converted into a known number of Class A shares. On June 24, 2015, the Bank received a complaint alleging that an employee had colluded with a bond issuer and an individual in misusing revenues pledged to municipal bonds for which the Bank served as trustee under the bond indenture. The Company conducted an investigation and concluded that employees in one of its Corporate Trust offices had, with respect to a single group of affiliated bond issuances, violated Company policies and procedures by waiving financial covenants, granting forbearances and accepting without disclosure to the bondholders, debt service payments from sources other than pledged revenues. The relationship manager was terminated. The Company reported the circumstances to, and cooperated with an investigation by, the Securities and Exchange Commission ("SEC"). On December 28, 2015, in an action brought by the SEC, the United States District Court for the District of New Jersey entered a judgment against the principals involved in issuing the bonds, precluding the principals from denying the alleged violations of the federal securities laws and requiring the principals to pay all outstanding principal, accrued interest, and other amounts required under the bond documents (now estimated to be approximately $48 million , less the value of the facilities securing repayment of the bonds), subject to oversight by a court appointed monitor. On September 7, 2016, the Bank agreed, and the SEC entered, a consent order finding that the Bank had violated Section 17(a) of the Securities Act of 1933 and Section 10(b) of the Securities Exchange Act and requiring the Bank to disgorge $1,067,721 of fees and pay a civil penalty of $600,000 . The Bank has disgorged the fees and paid the penalty. On August 26, 2016, the Bank was sued in the United States District Court for New Jersey by two bondholders in a putative class action on behalf of all holders of the bonds alleging the Bank participated in the fraudulent sale of securities by the principals. On September 14, 2016, the Bank was sued in the District Court of Tulsa County, Oklahoma by 19 bondholders alleging the Bank participated in the fraudulent sale of securities by the principals. Two separate small groups of bondholders have filed arbitration complaints with the Financial Institutions Regulatory Association respecting the bonds. Management has been advised by counsel that the Bank has valid defenses to the claims. On September 15, 2017, the principal of the bond issuances filed for protection under Chapter 11 of the United States Bankruptcy Code in the United States Bankruptcy Court for the Northern District of Georgia. The obligation of the principal to pay all principal and interest on the bonds is non-dischargeable in bankruptcy. The Bank expects the Court ordered payment plan will result in the payment of the bonds by the principals. Accordingly, no loss is probable at this time and no provision for loss has been made. If the payment plan does not result in payment of the bonds, a loss could become probable. A reasonable estimate cannot be made at this time though the amount could be material to the Company. On March 14, 2017, the Bank was sued in the United States District Court for the Northern District of Oklahoma by bondholders in a second putative class action representing a different set of municipal securities. The bondholders in this second action allege two individuals purchased facilities from the principals who are the subject of the SEC New Jersey proceedings by means of the fraudulent sale of $60 million of municipal securities for which the Bank also served as indenture trustee. The bondholders allege the Bank failed to disclose that the seller of the purchased facilities had engaged in the conduct complained of in the New Jersey action. The Bank properly performed all duties as indenture trustee of this second set of municipal securities, timely commenced proceedings against the issuer of the securities when default occurred, is cooperating with the SEC in actions against the two principals, is not a target of the SEC proceedings, and has been advised by counsel that the Bank has valid defenses to the claims of these bondholders. It is the opinion of management that no loss is probable at this time. The County of Bernalillo, New Mexico, commenced arbitration pursuant to the Arbitration Rules of FINRA seeking recovery of $5.6 million alleging that various municipal bonds purchased by the elected County Treasurer of Bernalillo County, New Mexico, from BOK Financial Securities, Inc. were unsuitable. The arbitration was conducted in July 2017. The arbitration panel found the County of Bernalillo’s complaint frivolous and awarded BOK Financial Securities, Inc. attorney fees and costs. The County has sued in the United States District Court for New Mexico to set aside the award of fees and costs to BOK Financial Securities but not the finding that the County's complaint was frivolous. On March 30, 2017, two deposit customers of the Bank sued the Bank in the District Court of Harris County, Texas. A judgment creditor had served a garnishment summons on the Bank. The deposit customers allege that, because the Bank was unable to produce adequate documentation of ownership of a series of deposit accounts at the Bank owned by them, they were compelled to enter into a settlement agreement with the judgment creditor pursuant to which the Bank paid $4.2 million from the accounts to the judgment creditor. The two deposit customers sought $7 million . The claim was mediated resulting in a settlement in which the Bank paid the plaintiffs $1 million . On March 7, 2017, a plaintiff filed a putative class action in the United States District Court for the Northern District of Texas alleging an extended overdraft fee charged by BOKF, NA is interest and exceeds permitted rates. BOKF, NA was previously sued in a class action in the United States District Court for the Northern District of Oklahoma making the same allegations. Pursuant to a motion to dismiss, the Northern District of Oklahoma Court action was dismissed. Other courts considering the question whether extended overdraft fees are interest have likewise determined such fees are not interest. BOKF, NA has moved to dismiss the action. The Northern District of Texas Action was dismissed upon motion by the Bank with leave granted the plaintiff to file an amended complaint. The plaintiff filed an amended complaint. The Bank has again moved to dismiss the complaint, which motion to dismiss is pending before the Court. Management is advised by counsel that a loss is not probable and that the loss, if any, cannot be reasonably estimated. In the ordinary course of business, BOK Financial and its subsidiaries are subject to legal actions and complaints. Management believes, based upon the opinion of counsel, that the actions and liability or loss, if any, resulting from the final outcomes of the proceedings, will not have a material effect on the Company’s financial condition, results of operations or cash flows. Alternative Investment Commitments The Company sponsors two private equity funds and invests in several tax credit entities and other funds as permitted by banking regulations. Consolidation of these investments is based on the variable interest model determined by the nature of the entity. Variable interest entities are generally defined as entities that either do not have sufficient equity to finance their activities without support from other parties or whose equity investors lack a controlling financial interest. Variable interest entities are consolidated based on the determination that the Company is the primary beneficiary including the power to direct the activities that most significantly impact the variable interest's economic performance and the obligation to absorb losses of the variable interest or the right to receive benefits of the variable interest that could be significant to the variable interest. BOKF Equity, LLC, an indirect wholly-owned subsidiary, is the general partner of two consolidated private equity funds (“the Funds”). The Funds provide alternative investment opportunities to certain customers, some of which are related parties, through unaffiliated limited partnerships. These unaffiliated limited partnerships generally invest in distressed assets, asset buy-outs or venture capital companies. As general partner, BOKF Equity, LLC has the power to direct activities that most significantly affect the Funds' performance and contingent obligations to make additional investments totaling $3.4 million at December 31, 2017 . Substantially all of the obligations are offset by limited partner commitments. The Company does not accrue its contingent liability to fund investments. The Volcker Rule in Title VI of the Dodd-Frank Act will limit both the amount and structure of these type of investments. Consolidated tax credit entities represent the Company's interest in entities earning federal new market tax credits related to qualifying loans for which the Company has the power to direct the activities that most significantly impact the variable interest's economic performance of the entity including being the primary beneficiary of or the obligation to absorb losses of the variable interest that could be significant to the variable interest. The creditors underlying the other borrowings of consolidated tax credit entities do not have recourse to the general credit of BOKF. The Company also has interests in various unrelated alternative investments generally consisting of unconsolidated limited partnership interests in or loans to entities for which investment return is in the form of tax credits or that invest in distressed real estate loans and properties, energy development, venture capital and other activities. The Company is prohibited by banking regulations from controlling or actively managing the activities of these investments and the Company's maximum exposure to loss is restricted to its investment balance. The Company's obligation to fund alternative investments is included in Other liabilities in the Consolidated Balance Sheets. A summary of consolidated and unconsolidated alternative investments as of December 31, 2017 and December 31, 2016 is as follows (in thousands): December 31, 2017 Loans Other Assets Other Liabilities Other Borrowings Non-controlling Interests Consolidated: Private equity funds $ — $ 14,783 $ — $ — $ 11,927 Tax credit entities 10,000 10,964 — 10,964 10,000 Other — 1,040 — — 1,040 Total consolidated $ 10,000 $ 26,787 $ — $ 10,964 $ 22,967 Unconsolidated: Tax credit entities $ 52,852 $ 153,506 $ 47,859 $ — $ — Other — 38,397 22,968 — — Total unconsolidated $ 52,852 $ 191,903 $ 70,827 $ — $ — December 31, 2016 Loans Other Other Other Non-controlling Consolidated: Private equity funds $ — $ 17,357 $ — $ — $ 13,237 Tax credit entities 10,000 11,585 — 10,964 10,000 Other — 29,783 3,189 1,092 8,266 Total consolidated $ 10,000 $ 58,725 $ 3,189 $ 12,056 $ 31,503 Unconsolidated: Tax credit entities $ 44,488 $ 143,715 $ 63,329 $ — $ — Other — 31,675 15,028 — — Total unconsolidated $ 44,488 $ 175,390 $ 78,357 $ — $ — Other Commitments and Contingencies Cavanal Hill Funds’ assets include U.S. Treasury and government securities money market funds. Assets of these funds consist of highly-rated, short-term obligations of the U.S. Treasury and Agencies. The net asset value of units in these funds was $1.00 at December 31, 2017 . An investment in these funds is not insured by the Federal Deposit Insurance Corporation or guaranteed by BOK Financial or any of its subsidiaries. BOK Financial may, but is not obligated to purchase assets from these funds to maintain the net asset value at $1.00 . No assets were purchased from the funds in 2017 or 2016 . Total rent expense for BOK Financial was $ 27.5 million in 2017 , $25.8 million in 2016 and $25.2 million in 2015 . At December 31, 2017 , future minimum lease payments for premises under operating leases were as follows: $18.9 million in 2018 , $19.3 million in 2019 , $17.1 million in 2020 , $15.0 million in 2021 , $9.7 million in 2022 and $73.0 million thereafter. BOKF, NA is obligated under a long-term lease for its bank premises in downtown Tulsa. The lease term, which began November 1, 1976, is for fifty-seven years with an option to terminate in 2024 with a two-year prior written notice. Premises leases may include options to renew at then current market rates and may include escalation provisions based upon changes in consumer price index or similar benchmarks. The Federal Reserve Bank requires member banks to maintain certain minimum average cash balances. Member banks may satisfy reserve balance requirements through holdings of vault cash and balances maintained directly with a Federal Reserve Bank. The combined average balance of vault cash and balances held at the Federal Reserve Bank was $1.9 billion for the year ended December 31, 2017 and $1.9 billion for the year ended December 31, 2016 .

Earnings Per Share

Earnings Per Share	12 Months Ended
	Dec. 31, 2017
Earnings Per Share [Abstract]
Earnings Per Share [Text Block]	Earnings Per Share The following table presents the computation of basic and diluted earnings per share (dollars in thousands, except per share data): Year Ended 2017 2016 2015 Numerator: Net income attributable to BOK Financial Corp. shareholders $ 334,644 $ 232,668 $ 288,565 Less: Earnings allocated to participating securities 3,561 2,883 3,383 Numerator for basic earnings per share – income available to common shareholders 331,083 229,785 285,182 Effect of reallocating undistributed earnings of participating securities 2 1 3 Numerator for diluted earnings per share – income available to common shareholders $ 331,085 $ 229,786 $ 285,185 Denominator: Weighted average shares outstanding 65,440,832 65,901,110 68,397,215 Less: Participating securities included in weighted average shares outstanding 695,468 815,483 802,526 Denominator for basic earnings per common share 64,745,364 65,085,627 67,594,689 Dilutive effect of employee stock compensation plans 1 60,920 58,271 96,969 Denominator for diluted earnings per common share 64,806,284 65,143,898 67,691,658 Basic earnings per share $ 5.11 $ 3.53 $ 4.22 Diluted earnings per share $ 5.11 $ 3.53 $ 4.21 1 Excludes employee stock options with exercise prices greater than current market price. — — —

Shareholders' Equity

Shareholders' Equity	12 Months Ended
	Dec. 31, 2017
Stockholders' Equity Note [Abstract]
Shareholders' Equity [Text Block]	Shareholders Equity Preferred Stock One billion shares of preferred stock with a par value of $0.00005 per share are authorized. The Series A Preferred Stock has no voting rights except as otherwise provided by Oklahoma corporate law and may be converted into one share of Common Stock for each 36 shares of Series A Preferred Stock at the option of the holder . Dividends are cumulative at an annual rate of ten percent of the $0.06 per share liquidation preference value when declared and are payable in cash. Aggregate liquidation preference is $15 million . No Series A Preferred Stock was outstanding in 2017 , 2016 or 2015 . Common Stock Common stock consists of 2.5 billion authorized shares with a $0.00006 par value. Holders of common shares are entitled to one vote per share at the election of the Board of Directors and on any question arising at any shareholders’ meeting and to receive dividends when and as declared. Additionally, regulations restrict the ability of national banks and bank holding companies to pay dividends. Subsidiary Bank The amounts of dividends that BOK Financial’s subsidiary bank can declare and the amounts of loans the subsidiary bank can extend to affiliates are limited by various federal banking regulations and state corporate law. Generally, dividends declared during a calendar year are limited to net profits, as defined, for the year plus retained profits for the preceding two years. The amounts of dividends are further restricted by minimum capital requirements. Regulatory Capital BOK Financial and the Bank are subject to various capital requirements administered by the federal banking agencies. Failure to meet minimum capital requirements can initiate certain mandatory and additional discretionary actions by regulators that could have a material effect on BOK Financial's operations. These capital requirements include quantitative measures of assets, liabilities and certain off-balance sheet items. The capital standards are also subject to qualitative judgments by the regulators. New capital rules were effective for BOK Financial on January 1, 2015. Components of these rules will phase in through January 1, 2019. A bank falling below the minimum capital requirements, including the capital conservation buffer, would be subject to regulatory restrictions on capital distributions (including but not limited to dividends and share repurchases) and executive bonus payments. For a banking institution to qualify as well capitalized, Common Equity Tier 1, Tier I, Total and Leverage capital ratios must be at least 6.5% , 8% , 10% and 5% , respectively. Tier I capital consists primarily of common stockholders' equity, excluding unrealized gains or losses on available for sale securities, less goodwill, core deposit premiums and certain other intangible assets. Total capital consists primarily of Tier I capital plus preferred stock, subordinated debt and allowances for credit losses, subject to certain limitations. The Bank exceeded the regulatory definition of well capitalized as of December 31, 2017 and December 31, 2016 . A summary of regulatory capital minimum requirements and levels follows (dollars in thousands): Minimum Capital Requirement Capital Conservation Buffer 1 Minimum Capital Requirement Including Capital Conservation Buffer December 31, 2017 December 31, 2016 Common Equity Tier 1 Capital (to Risk Weighted Assets): Consolidated 4.50% 2.50% 7.00% 3,074,981 12.05 % $ 2,834,532 11.21 % BOKF, NA 4.50% N/A 4.50% 2,870,694 11.34 % 2,609,450 10.65 % Mobank 2 4.50% N/A 4.50% N/A N/A 54,616 10.03 % Tier I Capital (to Risk Weighted Assets): Consolidated 6.00% 2.50% 8.50% $ 3,074,981 12.05 % $ 2,834,532 11.21 % BOKF, NA 6.00% N/A 6.00% 2,870,694 11.34 % 2,609,450 10.65 % Mobank 2 6.00% N/A 6.00% N/A N/A 54,616 10.03 % Total Capital (to Risk Weighted Assets): Consolidated 8.00% 2.50% 10.50% $ 3,455,709 13.54 % $ 3,238,323 12.81 % BOKF, NA 8.00% N/A 8.00% 3,105,117 12.27 % 2,866,949 11.70 % Mobank 2 8.00% N/A 8.00% N/A N/A 54,617 10.03 % Leverage (Tier I Capital to Average Assets): Consolidated 4.00% N/A 4.00% $ 3,074,981 9.31 % $ 2,834,532 8.72 % BOKF, NA 4.00% N/A 4.00% 2,870,694 8.73 % 2,609,450 8.11 % Mobank 2 4.00% N/A 4.00% N/A N/A 54,616 8.37 % 1 Capital conservation buffer is effective January 1, 2016 and is phased in through 2019. The phased in capital conservation buffer was 1.25% at December 31, 2017 and 0.625% at December 31, 2016 . The fully phased in requirement of 2.50% is included in the table above. 2 Missouri Bank and Trust Company of Kansas City dba Mobank was acquired by BOK Financial effective December 1, 2016 and was merged into BOKF, NA effective February 17, 2017. Accumulated Other Comprehensive Income (Loss) AOCI includes unrealized gains and losses on available for sale ("AFS") securities and non-credit related unrealized losses on AFS securities for which an other-than-temporary impairment has been recorded in earnings. AOCI also includes unrealized gains on AFS securities that were transferred from AFS to investment securities in 2011. Such amounts were amortized over the estimated remaining life of the security as an adjustment to yield, offsetting the related amortization of premium on the transferred securities. Unrealized losses on employee benefit plans will be reclassified into income as pension plan costs are recognized over the remaining service period of plan participants. Accumulated losses on the interest rate lock hedge of the subordinated debt issuance in 2005 were reclassified into income over the ten-year life of the debt. Gains and losses in AOCI are net of deferred income taxes. A rollforward of the components of accumulated other comprehensive income (loss) is included as follows (in thousands): Unrealized Gain (Loss) on Available for Sale Securities Investment Securities Transferred from AFS Employee Benefit Plans Loss on Effective Cash Flow Hedges Total Balance, December 31, 2014 $ 59,239 $ 376 $ (2,868 ) $ (74 ) $ 56,673 Net change in unrealized gain (loss) (48,607 ) — 1,804 — (46,803 ) Reclassification adjustments included in earnings: Interest revenue, Investment securities, Taxable securities — (503 ) — — (503 ) Interest expense, Subordinated debentures — — — 121 121 Net impairment losses recognized in earnings 1,819 — — — 1,819 Gain on available for sale securities, net (12,058 ) — — — (12,058 ) Other comprehensive income (loss), before income taxes (58,846 ) (503 ) 1,804 121 (57,424 ) Federal and state income tax 1 (22,891 ) (195 ) 701 47 (22,338 ) Other comprehensive income (loss), net of income taxes (35,955 ) (308 ) 1,103 74 (35,086 ) Balance, December 31, 2015 23,284 68 (1,765 ) — 21,587 Net change in unrealized gain (loss) (41,333 ) — (188 ) — (41,521 ) Reclassification adjustments included in earnings: Interest revenue, Investment securities, Taxable securities — (112 ) — — (112 ) Interest expense, Subordinated debentures — — — — — Net impairment losses recognized in earnings — — — — — Gain on available for sale securities, net (11,675 ) — — — (11,675 ) Other comprehensive income (loss), before income taxes (53,008 ) (112 ) (188 ) — (53,308 ) Federal and state income tax 1 (20,637 ) (44 ) (73 ) — (20,754 ) Other comprehensive income (loss), net of income taxes (32,371 ) (68 ) (115 ) — (32,554 ) Balance, December 31, 2016 (9,087 ) — (1,880 ) — (10,967 ) Net change in unrealized gain (loss) (28,170 ) — 2,018 — (26,152 ) Reclassification adjustments included in earnings: Interest revenue, Investment securities, Taxable securities — — — — — Interest expense, Subordinated debentures — — — — — Net impairment losses recognized in earnings — — — — — Gain on available for sale securities, net (4,428 ) — — — (4,428 ) Other comprehensive income (loss), before income taxes (32,598 ) — 2,018 — (30,580 ) Federal and state income tax 1 (12,708 ) — 785 — (11,923 ) Other comprehensive income (loss), net of income taxes (19,890 ) — 1,233 — (18,657 ) Reclassification of stranded accumulated other comprehensive loss related to tax reform (6,408 ) — (142 ) — (6,550 ) Balance, December 31, 2017 $ (35,385 ) $ — $ (789 ) $ — $ (36,174 ) 1 Calculated using 39% effective tax rate.

Reportable Segments

Reportable Segments	12 Months Ended
	Dec. 31, 2017
Segment Reporting [Abstract]
Reportable Segments [Text Block]	Reportable Segments BOK Financial operates three principal lines of business: Commercial Banking, Consumer Banking and Wealth Management. Commercial Banking includes lending, treasury and cash management services and customer risk management products to small businesses, middle market and larger commercial customers. Commercial Banking also includes the TransFund EFT network. Consumer Banking includes retail lending and deposit services, lending and deposit services to small business customers served through the consumer branch network and all mortgage banking activities. Wealth Management provides fiduciary services, private bank services and investment advisory services in all markets. Wealth Management also underwrites state and municipal securities and engages in brokerage and trading activities. In addition to its lines of business, BOK Financial has a Funds Management unit. The primary purpose of this unit is to manage overall liquidity needs and interest rate risk. Each line of business borrows funds from and provides funds to the Funds Management unit as needed to support their operations. Operating results for Funds Management and other include the effect of interest rate risk positions and risk management activities, securities gains and losses including impairment charges, the provision for credit losses in excess of net loans charged off, tax planning strategies and certain executive compensation costs that are not attributed to the lines of business. BOK Financial allocates resources and evaluates performance of its lines of business after allocation of funds, actual net credit losses and capital costs. In addition, we measure the performance of our business lines after allocation of certain indirect expenses and taxes on statutory rates. The allocation for the prior comparable periods have been revised on a comparable basis. The cost of funds borrowed from the Funds Management unit by the operating lines of business is transfer priced at rates that approximate market rates for funds with similar duration. Market rates are generally based on the applicable LIBOR or interest rate swap rates, adjusted for prepayment risk. This method of transfer-pricing funds that support assets of the operating lines of business tends to insulate them from interest rate risk. The value of funds provided by the operating lines of business to the Funds Management unit is based on rates which approximate the wholesale market rates for funds with similar duration and re-pricing characteristics. Market rates are generally based on LIBOR or interest rate swap rates. The funds credit formula applied to deposit products with indeterminate maturities is established based on their re-pricing characteristics reflected in a combination of the short-term LIBOR rates and a moving average of an intermediate term swap rate, with an appropriate spread applied to both. Shorter duration products are weighted towards the short-term LIBOR rate and longer duration products are weighted towards intermediate swap rates. The expected duration ranges from 30 days for certain rate-sensitive deposits to five years. Substantially all revenue is from domestic customers. No single external customer accounts for more than 10% of total revenue. Net loans charged off and provision for credit losses represents net loans charged off as attributed to the lines of business and the provision for credit losses in excess of net charge-offs attributed to Funds Management and Other. The acquisition of Mobank on December 1, 2016 was allocated to the operating segments on February 21, 2017 when Mobank was mered into BOKF, NA. Operations, assets and liabilities of Mobank were included in Funds Management and Other during this time period. Reportable segments reconciliation to the Consolidated Financial Statements for the year ended December 31, 2017 is as follows (in thousands): Commercial Consumer Wealth Management Funds Management and Other BOK Financial Consolidated Net interest and dividend revenue from external sources $ 588,938 $ 96,360 $ 45,024 $ 111,379 $ 841,701 Net interest revenue (expense) from internal sources (84,290 ) 47,218 38,344 (1,272 ) — Net interest and dividend revenue 504,648 143,578 83,368 110,107 841,701 Provision for credit losses 13,881 4,783 (696 ) (24,968 ) (7,000 ) Net interest and dividend revenue after provision for credit losses 490,767 138,795 84,064 135,075 848,701 Other operating revenue 206,110 196,231 301,434 (8,681 ) 695,094 Other operating expense 226,334 224,323 246,626 328,234 1,025,517 Net direct contribution 470,543 110,703 138,872 (201,840 ) 518,278 Gain (loss) on financial instruments, net 52 (3,331 ) — 3,279 — Change in fair value of mortgage servicing rights — 172 — (172 ) — Gain (loss) on repossessed assets, net (2,681 ) 223 387 2,071 — Corporate expense allocations 33,958 67,761 40,562 (142,281 ) — Net income before taxes 433,956 40,006 98,697 (54,381 ) 518,278 Federal and state income taxes 168,809 15,562 38,393 (40,171 ) 182,593 Net income 265,147 24,444 60,304 (14,210 ) 335,685 Net income attributable to non-controlling interests — — — 1,041 1,041 Net income attributable to BOK Financial Corp. shareholders $ 265,147 $ 24,444 $ 60,304 $ (15,251 ) $ 334,644 Average assets $ 17,517,217 $ 8,956,713 $ 7,072,622 $ (599,058 ) $ 32,947,494 Reportable segments reconciliation to the Consolidated Financial Statements for the year ended December 31, 2016 is as follows (in thousands): Commercial Consumer Wealth Management Funds Management and Other BOK Financial Consolidated Net interest and dividend revenue from external sources $ 492,967 $ 85,998 $ 33,006 $ 135,257 $ 747,228 Net interest revenue (expense) from internal sources (58,781 ) 37,777 29,043 (8,039 ) — Net interest and dividend revenue 434,186 123,775 62,049 127,218 747,228 Provision for credit losses 32,959 4,927 (801 ) 27,915 65,000 Net interest and dividend revenue after provision for credit losses 401,227 118,848 62,850 99,303 682,228 Other operating revenue 195,521 224,802 283,222 (29,525 ) 674,020 Other operating expense 216,451 249,744 250,994 300,401 1,017,590 Net direct contribution 380,297 93,906 95,078 (230,623 ) 338,658 Gain (loss) on financial instruments, net 10 (26,252 ) (42 ) 26,284 — Change in fair value of mortgage servicing rights — (2,193 ) — 2,193 — Gain on repossessed assets, net 669 979 — (1,648 ) — Corporate expense allocations 35,760 66,411 42,378 (144,549 ) — Net income before taxes 345,216 29 52,658 (59,245 ) 338,658 Federal and state income taxes 134,289 11 20,484 (48,407 ) 106,377 Net income 210,927 18 32,174 (10,838 ) 232,281 Net loss attributable to non-controlling interests — — — (387 ) (387 ) Net income attributable to BOK Financial Corp. shareholders $ 210,927 $ 18 $ 32,174 $ (10,451 ) $ 232,668 Average assets $ 16,998,626 $ 8,722,372 $ 6,281,127 $ 276,277 $ 32,278,402 Reportable segments reconciliation to the Consolidated Financial Statements for the year ended December 31, 2015 is as follows (in thousands): Commercial Consumer Wealth Management Funds Management and Other BOK Financial Consolidated Net interest and dividend revenue from external sources $ 439,751 $ 84,848 $ 24,744 $ 154,011 $ 703,354 Net interest revenue (expense) from internal sources (52,313 ) 28,503 24,043 (233 ) — Net interest and dividend revenue 387,438 113,351 48,787 153,778 703,354 Provision for credit losses (6,748 ) 6,934 (1,083 ) 34,897 34,000 Net interest and dividend revenue after provision for credit losses 394,186 106,417 49,870 118,881 669,354 Other operating revenue 177,729 218,095 267,523 (4,867 ) 658,480 Other operating expense 202,804 203,070 228,664 261,653 896,191 Net direct contribution 369,111 121,442 88,729 (147,639 ) 431,643 Loss on financial instruments, net — (4,712 ) (204 ) 4,916 — Change in fair value of mortgage servicing rights — (4,853 ) — 4,853 — Gain on repossessed assets, net 708 916 — (1,624 ) — Corporate expense allocations 43,279 74,936 40,357 (158,572 ) — Net income before taxes 326,540 37,857 48,168 19,078 431,643 Federal and state income taxes 127,024 14,726 18,737 (21,103 ) 139,384 Net income 199,516 23,131 29,431 40,181 292,259 Net income attributable to non-controlling interests — — — 3,694 3,694 Net income attributable to BOK Financial Corp. shareholders $ 199,516 $ 23,131 $ 29,431 $ 36,487 $ 288,565 Average assets $ 16,284,527 $ 8,836,327 $ 5,444,483 $ 9,418 $ 30,574,755

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Fair Value Measurements [Text Block]	Fair Value Measurements Fair value is defined by applicable accounting guidance as the price to sell an asset or transfer a liability in an orderly transaction between market participants in the principal market for the given asset or liability at the measurement date based on market conditions at that date. An orderly transaction assumes exposure to the market for a customary period for marketing activities prior to the measurement date and not a forced liquidation or distressed sale. Certain assets and liabilities are recorded in the Company’s financial statements at fair value. Some are recorded on a recurring basis and some on a non-recurring basis. For some assets and liabilities, observable market transactions and market information might be available. For other assets and liabilities, observable market transactions and market information might not be available. A hierarchy for fair value has been established which categorizes into three levels the inputs to valuation techniques used to measure fair value. The three levels are as follows: Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1) - fair value is based on unadjusted quoted prices in active markets for identical assets or liabilities. Significant Other Observable Inputs (Level 2) - fair value is based on significant other observable inputs which are generally determined based on a single price for each financial instrument provided to us by an applicable third-party pricing service and is based on one or more of the following: • Quoted prices for similar, but not identical, assets or liabilities in active markets; • Quoted prices for identical or similar assets or liabilities in inactive markets; • Inputs other than quoted prices that are observable, such as interest rate and yield curves, volatilities, prepayment speeds, loss severities, credit risks and default rates; • Other inputs derived from or corroborated by observable market inputs. Significant Unobservable Inputs (Level 3) - fair value is based upon model-based valuation techniques for which at least one significant assumption is not observable in the market. Transfers between levels are recognized as of the end of the reporting period. There were no transfers in or out of quoted prices in active markets for identical instruments to significant other observable inputs or significant unobservable inputs during the year ended December 31, 2017 and 2016 , respectively. Transfers between significant other observable inputs and significant unobservable inputs during the year ended December 31, 2017 and 2016 are included in the summary of changes in recurring fair values measured using unobservable inputs. The underlying methods used by the third-party pricing services are considered in determining the primary inputs used to determine fair values. Management has evaluated the methodologies employed by the third-party pricing services by comparing the price provided by the pricing service with other sources, including brokers' quotes, sales or purchases of similar instruments and discounted cash flows to establish a basis for reliance on the pricing service values. Significant differences between the pricing service provided value and other sources are discussed with the pricing service to understand the basis for their values. Based on all observable inputs, management may adjust prices obtained from third-party pricing services to more appropriately reflect the prices that would be received to sell assets or paid to transfer liabilities in orderly transactions in the current market. No significant adjustments were made to prices provided by third-party pricing services at December 31, 2017 and 2016 . Assets and Liabilities Measured at Fair Value on a Recurring Basis The fair value of financial assets and liabilities that are measured on a recurring basis is as follows as of December 31, 2017 (in thousands): Total Quoted Prices in Active Markets for Identical Instruments Significant Other Observable Inputs Significant Unobservable Inputs Assets: Trading securities: U.S. government agency debentures $ 21,196 $ — $ 21,196 $ — U.S. agency residential mortgage-backed securities 392,673 — 392,673 — Municipal and other tax-exempt securities 13,559 — 13,559 — Asset-backed securities 23,885 — 23,885 — Other trading securities 11,363 — 11,363 — Total trading securities 462,676 — 462,676 — Available for sale securities: U.S. Treasury securities 1,000 1,000 — — Municipal and other tax-exempt securities 27,080 — 22,278 4,802 U.S. government agency residential mortgage-backed securities 5,309,152 — 5,309,152 — Privately issued residential mortgage-backed securities 93,221 — 93,221 — Commercial mortgage-backed securities guaranteed by U.S. government agencies 2,834,961 — 2,834,961 — Other debt securities 25,481 — 25,009 472 Perpetual preferred stock 15,767 — 15,767 — Equity securities and mutual funds 14,916 — 14,916 — Total available for sale securities 8,321,578 1,000 8,315,304 5,274 Fair value option securities – U.S. government agency residential mortgage-backed securities 755,054 — 755,054 — Residential mortgage loans held for sale 221,378 — 209,079 12,299 Mortgage servicing rights, net 1 252,867 — — 252,867 Derivative contracts, net of cash margin 2 220,502 8,179 212,323 — Liabilities: Derivative contracts, net of cash margin 2 171,963 — 171,963 — 1 A reconciliation of the beginning and ending fair value of mortgage servicing rights and disclosures of significant assumptions used to determine fair value are presented in Note 7 , Mortgage Banking Activities. 2 See Note 3 for detail of fair value of derivative contracts by contract type. Derivative contracts in a net asset position that were valued based on quoted prices in active markets or identical instruments (Level 1) are exchange-traded interest rate, energy and agricultural derivative contracts, net of cash margin. Derivative contracts in a net liability position that were valued using quoted prices in active markets for identical instruments (Level 1) are exchange-traded interest rate and energy derivative contracts, fully offset by cash margin. The fair value of financial assets and liabilities that are measured on a recurring basis is as follows as of December 31, 2016 (in thousands): Total Quoted Prices in Active Markets for Identical Instruments Significant Other Observable Inputs Significant Unobservable Inputs Assets: Trading securities: U.S. government agency debentures $ 6,234 $ — $ 6,234 $ — U.S. government agency residential mortgage-backed securities 310,067 — 310,067 — Municipal and other tax-exempt securities 14,427 — 14,427 — Asset-backed securities — — — — Other trading securities 6,900 — 6,900 — Total trading securities 337,628 — 337,628 — Available for sale securities: U.S. Treasury securities 999 999 — — Municipal and other tax-exempt securities 40,993 — 35,204 5,789 U.S. government agency residential mortgage-backed securities 5,460,386 — 5,460,386 — Privately issued residential mortgage-backed securities 115,535 — 115,535 — Commercial mortgage-backed securities guaranteed by U.S. government agencies 3,017,933 — 3,017,933 — Other debt securities 4,152 — — 4,152 Perpetual preferred stock 18,474 — 18,474 — Equity securities and mutual funds 18,357 3,495 14,862 — Total available for sale securities 8,676,829 4,494 8,662,394 9,941 Fair value option securities – U.S. government agency residential mortgage-backed securities 77,046 — 77,046 — Residential mortgage loans held for sale 301,897 — 290,280 11,617 Mortgage servicing rights, net 1 247,073 — — 247,073 Derivative contracts, net of cash margin 2 689,872 7,541 682,331 — Liabilities: Derivative contracts, net of cash margin 2 664,531 6,972 657,559 — 1 A reconciliation of the beginning and ending fair value of mortgage servicing rights and disclosures of significant assumptions used to determine fair value are presented in Note 7 , Mortgage Banking Activities. 2 See Note 3 for detail of fair value of derivative contracts by contract type. Derivative contracts in a net asset position that were valued based on quoted prices in active markets for identical instruments (Level 1) are exchange-traded interest rate and energy derivative contracts, net of cash margin. Derivative contracts in a net liability position that were valued using quoted prices in active markets for identical instruments based on quoted prices in active markets for identical instruments (Level 1) are exchange-traded interest rate, energy and agricultural derivative contracts, net of cash margin. Following is a description of the Company's valuation methodologies used for assets and liabilities measured on a recurring basis: Securities The fair values of trading, available for sale and fair value option securities are based on quoted prices for identical instruments in active markets, when available. If quoted prices for identical instruments are not available, fair values are based on significant other observable inputs such as quoted prices of comparable instruments or interest rates and credit spreads, yield curves, volatilities, prepayment speeds and loss severities. The fair value of certain available for sale municipal and other debt securities may be based on significant unobservable inputs. These significant unobservable inputs include limited observed trades, projected cash flows, current credit rating of the issuers and, when applicable, the insurers of the debt and observed trades of similar debt. Discount rates are primarily based on reference to interest rate spreads on comparable securities of similar duration and credit rating as determined by the nationally-recognized rating agencies adjusted for a lack of trading volume. Significant unobservable inputs are developed by investment securities professionals involved in the active trading of similar securities. A summary of significant inputs used to value these securities follows. A management committee composed of senior members from the Company's Capital Markets, Risk Management and Finance departments assess the appropriateness of these inputs quarterly. Derivatives All derivative instruments are carried on the balance sheet at fair value. Fair values for exchange-traded contracts are based on quoted prices. Fair values for over-the-counter interest rate, commodity and foreign exchange contracts are based on valuations provided either by third-party dealers in the contracts, quotes provided by independent pricing services, or a third-party provided pricing model that uses significant other observable market inputs. Credit risk is considered in determining the fair value of derivative instruments. Management determines fair value adjustments based on various risk factors including but not limited to counterparty credit rating or equivalent loan grading, derivative contract notional size, price volatility of the underlying commodity, duration of the derivative contracts and expected loss severity. Expected loss severity is based on historical losses for similarly risk graded commercial loan customers. Decreases in counterparty credit rating or grading and increases in price volatility and expected loss severity all tend to increase the credit quality adjustment which reduces the fair value of asset contracts. We also consider our own credit risk in determining the fair value of derivative contracts. Changes in our credit rating would affect the fair value of our derivative liabilities. In the event of a credit downgrade, the fair value of our derivative liabilities would increase. Residential Mortgage Loans Held for Sale Residential mortgage loans held for sale are carried on the balance sheet at fair value. The fair values of conforming residential mortgage loans held for sale are based upon quoted market prices of such loans sold in securitization transactions, including related unfunded loan commitments. The fair value of mortgage loans that are unable to be sold to U.S. government agencies is determined using quoted prices of loans that are sold in securitization transactions with a liquidity discount applied. The following represents the changes related to assets measured at fair value on a recurring basis using significant unobservable inputs (in thousands): Available for Sale Securities Residential mortgage loans held for sale Municipal and other tax-exempt securities Other debt securities Balance, December 31, 2015 $ 9,610 $ 4,151 $ 7,874 Transfer to Level 3 from Level 2 1 — — 6,631 Purchases and capital calls — — — Redemptions and distributions (3,975 ) — — Proceeds from sales — — (2,540 ) Gain (loss) recognized in earnings: Mortgage banking revenue — — (348 ) Other comprehensive income (loss): Net change in unrealized gain (loss) 154 1 — Balance, December 31, 2016 5,789 4,152 11,617 Transfer to Level 3 from Level 2 1 — — 3,507 Purchases and capital calls — — — Redemptions and distributions (1,100 ) — — Proceeds from sales — (3,900 ) (2,944 ) Gain (loss) recognized in earnings: Mortgage banking revenue — — 119 Other comprehensive income (loss): Net change in unrealized gain (loss) 113 220 — Balance, December 31, 2017 $ 4,802 $ 472 $ 12,299 1 Recurring transfers to Level 3 from Level 2 consist of residential mortgage loans intended for sale to U.S. government agencies that fail to meet conforming standards. A summary of quantitative information about assets measured at fair value on a recurring basis using significant unobservable inputs (Level 3) as of December 31, 2017 follows (in thousands): Quantitative Information about Level 3 Recurring Fair Value Measurements Par Value Amortized Cost/Unpaid Principal Balance Fair Value Valuation Technique(s) Significant Unobservable Input Range (Weighted Average) Available for sale securities: Municipal and other tax-exempt securities $ 5,095 $ 5,068 $ 4,802 Discounted cash flows 1 Interest rate spread 6.60%-6.60% (6.60%) 2 92.25%-94.76% (93.75%) 3 Other debt securities 500 500 472 Discounted cash flows 1 Interest rate spread 6.85% - 6.85% (6.85%) 4 94.39% - 94.39% (94.39%) 3 Residential mortgage loans held for sale N/A 12,981 12,299 Quoted prices of loans sold in securitization transactions, with a liquidity discount applied Liquidity discount applied to the market value of mortgage loans qualifying for sale to U.S. government agencies 94.75% 1 Discounted cash flows developed using discount rates primarily based on reference to interest rate spreads for comparable securities of similar duration and credit rating as determined by the nationally-recognized rating agencies, adjusted for lack of trading volume. 2 Interest rate yields used to value investment grade tax-exempt securities represent a spread of 372 to 466 basis points over average yields for comparable tax-exempt securities. 3 Represents fair value as a percentage of par value. 4 Interest rate yields used to value investment grade taxable securities based on comparable short-term taxable securities which are generally yielding approximately 3% . A summary of quantitative information about Recurring Fair Value Measurements based on Significant Unobservable Inputs (Level 3) as of December 31, 2016 follows (in thousands): Quantitative Information about Level 3 Recurring Fair Value Measurements Par Value Amortized Cost 6 Fair Value Valuation Technique(s) Significant Unobservable Input Range (Weighted Average) Available for sale securities: Municipal and other tax-exempt securities $ 6,195 $ 6,163 $ 5,789 Discounted cash flows 1 Interest rate spread 5.91%-6.21% (6.16%) 2 90.00%-93.40% (92.20%) 3 Other debt securities 4,400 4,400 4,152 Discounted cash flows 1 Interest rate spread 6.01% - 6.26% (6.23%) 4 94.34% - 94.36% (94.36%) 3 Residential mortgage loans held for sale N/A 12,431 11,617 Quoted prices of loans sold in securitization transactions, with a liquidity discount applied Liquidity discount applied to the market value of mortgage loans qualifying for sale to U.S. government agencies 93.45% 1 Discounted cash flows developed using discount rates primarily based on reference to interest rate spreads for comparable securities of similar duration and credit rating as determined by the nationally-recognized rating agencies, adjusted for lack of trading volume. 2 Interest rate yields used to value investment grade tax-exempt securities represent a spread of 467 to 525 basis points over average yields for comparable tax-exempt securities. 3 Represents fair value as a percentage of par value. 4 Interest rate yields used to value investment grade taxable securities based on comparable short-term taxable securities which are generally yielding less than 1% . Fair Value of Assets and Liabilities Measured on a Non-Recurring Basis Assets measured at fair value on a non-recurring basis include pension plan assets, which are based on quoted prices in active markets for identical instruments, collateral for certain impaired loans and real property and other assets acquired to satisfy loans, which are based primarily on comparisons to completed sales of similar assets. See Note 6 for information related to the non-recurring fair value measurement of Mobank. The following represents the carrying value of assets measured at fair value on a non-recurring basis and related losses recorded during the year. The carrying value represents only those assets with the balance sheet date for which the fair value was adjusted during the year: Carrying Value at December 31, 2017 Fair Value Adjustments for the Quoted Prices in Active Markets for Identical Instruments Significant Other Observable Inputs Significant Unobservable Inputs Gross charge-offs against allowance for loan losses Net losses and expenses of repossessed assets, net Impaired loans $ — $ 7,436 $ 7,626 $ 12,145 $ — Real estate and other repossessed assets — 3,483 5,481 — 6,372 Carrying Value at December 31, 2016 Fair Value Adjustments for the Quoted Prices in Active Markets for Identical Instruments Significant Other Observable Inputs Significant Unobservable Inputs Gross charge-offs against allowance for loan losses Net losses and expenses of repossessed assets, net Impaired loans $ — $ 539 $ 11,295 $ 7,594 $ — Real estate and other repossessed assets — 7,965 2,192 — 2,527 The fair value of collateral-dependent impaired loans and real estate and other repossessed assets and the related fair value adjustments are generally based on unadjusted third-party appraisals. Our appraisal review policies require appraised values to be supported by observed inputs derived principally from or corroborated by observable market data. Appraisals that are not based on observable inputs or that require significant adjustments or fair value measurements that are not based on third-party appraisals are considered to be based on significant unobservable inputs. Non-recurring fair value measurements of collateral-dependent impaired loans and real estate and other repossessed assets based on significant unobservable inputs are generally due to estimates of current fair values between appraisal dates. Significant unobservable inputs include listing prices for comparable assets, uncorroborated expert opinions or management's knowledge of the collateral or industry. Non-recurring fair value measurements of collateral dependent loans secured by mineral rights are generally determined by our internal staff of engineers on projected cash flows under current market conditions and are based on significant unobservable inputs. Projected cash flows are discounted according to risk characteristics of the underlying oil and gas properties. Assets are evaluated to demonstrate with reasonable certainty that crude oil, natural gas and natural gas liquids can be recovered from known oil and gas reservoirs under existing economic and operating conditions at current prices with existing conventional equipment, operating methods and costs. Significant unobservable inputs are developed by asset management and workout professionals and approved by senior Credit Administration executives. A summary of quantitative information about Non-recurring Fair Value Measurements based on Significant Unobservable Inputs (Level 3) as of December 31, 2017 follows (in thousands): Quantitative Information about Level 3 Non-recurring Fair Value Measurements Fair Value Valuation Technique(s) Significant Unobservable Input Range (Weighted Average) Impaired loans $ 7,626 Discounted cash flows Recoverable oil and gas reserves, forward-looking commodity prices and estimated operating costs 40% - 86% (59%) 1 Real estate and other repossessed assets 5,481 Discounted cash flows Recoverable oil and gas reserves, forward-looking commodity prices, estimated operating costs N/A 1 Represents fair value as a percentage of the unpaid principal balance. A summary of quantitative information about Non-recurring Fair Value Measurements based on Significant Unobservable Inputs (Level 3) as of December 31, 2016 follows (in thousands): Quantitative Information about Level 3 Non-recurring Fair Value Measurements Fair Value Valuation Technique(s) Significant Unobservable Input Range (Weighted Average) Impaired loans $ 11,295 Discounted cash flows Recoverable oil and gas reserves, forward-looking commodity prices and estimated operating costs 22% - 59% (57%) 1 Real estate and other repossessed assets 2,192 Appraised value, as adjusted Marketability adjustments off appraised value 2 70% - 87% (74%) 1 Represents fair value as a percentage of the unpaid principal balance. 2 Marketability adjustments include consideration of estimated costs to sell which is approximately 10% of the fair value. The fair value of pension plan assets was approximately $40 million at December 31, 2017 and $42 million at December 31, 2016 , determined by significant other observable inputs. Fair value adjustments of pension plan assets along with changes in the projected benefit obligation are recognized in other comprehensive income. Fair Value of Financial Instruments The following table presents the carrying values and estimated fair values of all financial instruments, including those financial assets and liabilities that are not measured and reported at fair value on a recurring basis or non-recurring (dollars in thousands): December 31, 2017 Carrying Value Estimated Fair Value Quoted Prices in Active Markets for Identical Instruments (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Cash and due from banks $ 602,510 602,510 602,510 — — Interest-bearing cash and cash equivalents 1,714,544 1,714,544 1,714,544 — — Trading securities: U.S. government agency debentures 21,196 21,196 — 21,196 — U.S. government agency residential mortgage-backed securities 392,673 392,673 — 392,673 — Municipal and other tax-exempt securities 13,559 13,559 — 13,559 — Asset-backed securities 23,885 23,885 — 23,885 — Other trading securities 11,363 11,363 — 11,363 — Total trading securities 462,676 438,791 — 438,791 — Investment securities: Municipal and other tax-exempt securities 228,186 230,349 — 230,349 — U.S. government agency residential mortgage-backed securities 15,891 16,242 — 16,242 — Other debt securities 217,716 233,444 — 233,444 — Total investment securities 461,793 480,035 — 480,035 — Available for sale securities: U.S. Treasury securities 1,000 1,000 1,000 — — Municipal and other tax-exempt securities 27,080 27,080 — 22,278 4,802 U.S. government agency residential mortgage-backed securities 5,309,152 5,309,152 — 5,309,152 — Privately issued residential mortgage-backed securities 93,221 93,221 — 93,221 — Commercial mortgage-backed securities guaranteed by U.S. government agencies 2,834,961 2,834,961 — 2,834,961 — Other debt securities 25,481 25,481 — 25,009 472 Perpetual preferred stock 15,767 15,767 — 15,767 — Equity securities and mutual funds 14,916 14,916 — 14,916 — Total available for sale securities 8,321,578 8,321,578 1,000 8,315,304 5,274 Fair value option securities – U.S. government agency residential mortgage-backed securities 755,054 755,054 — 755,054 — Residential mortgage loans held for sale 221,378 221,378 — 208,946 12,432 Loans: Commercial 10,733,975 10,524,627 — — 10,524,627 Commercial real estate 3,479,987 3,428,733 — — 3,428,733 Residential mortgage 1,973,686 1,977,721 — — 1,977,721 Personal 965,776 956,706 — — 956,706 Total loans 17,153,424 16,887,787 — — 16,887,787 Allowance for loan losses (230,682 ) — — — — Loans, net of allowance 16,922,742 16,887,787 — — 16,887,787 Mortgage servicing rights 252,867 252,867 — — 252,867 Derivative instruments with positive fair value, net of cash margin 220,502 220,502 8,179 212,323 — Deposits with no stated maturity 19,962,889 19,962,889 — — 19,962,889 Time deposits 2,098,416 2,064,558 — — 2,064,558 Other borrowed funds 5,709,860 5,703,121 — — 5,703,121 Subordinated debentures 144,677 148,207 — 148,207 — Derivative instruments with negative fair value, net of cash margin 171,963 171,963 — 171,963 — December 31, 2016 Carrying Value Estimated Fair Value Quoted Prices in Active Markets for Identical Instruments (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Cash and due from banks $ 620,846 $ 620,846 620,846 — $ — Interest-bearing cash and cash equivalents 1,916,651 1,916,651 1,916,651 — — Trading securities: U.S. government agency debentures 6,234 6,234 — 6,234 — U.S. government agency residential mortgage-backed securities 310,067 310,067 — 310,067 — Municipal and other tax-exempt securities 14,427 14,427 — 14,427 — Asset-backed securities — — — — — Other trading securities 6,900 6,900 — 6,900 — Total trading securities 337,628 337,628 — 337,628 — Investment securities: Municipal and other tax-exempt securities 320,364 321,225 — 321,225 — U.S. government agency residential mortgage-backed securities 20,777 21,473 — 21,473 — Other debt securities 205,004 222,795 — 222,795 — Total investment securities 546,145 565,493 — 565,493 — Available for sale securities: U.S. Treasury securities 999 999 999 — — Municipal and other tax-exempt securities 40,993 40,993 — 35,204 5,789 U.S. government agency residential mortgage-backed securities 5,460,386 5,460,386 — 5,460,386 — Privately issued residential mortgage-backed securities 115,535 115,535 — 115,535 — Commercial mortgage-backed securities guaranteed by U.S. government agencies 3,017,933 3,017,933 — 3,017,933 — Other debt securities 4,152 4,152 — — 4,152 Perpetual preferred stock 18,474 18,474 — 18,474 — Equity securities and mutual funds 18,357 18,357 3,495 14,862 — Total available for sale securities 8,676,829 8,676,829 4,494 8,662,394 9,941 Fair value option securities – U.S. government agency residential mortgage-backed securities 77,046 77,046 — 77,046 — Residential mortgage loans held for sale 301,897 301,897 — 290,280 11,617 Loans: Commercial 10,390,824 10,437,016 — — 10,437,016 Commercial real estate 3,809,046 3,850,981 — — 3,850,981 Residential mortgage 1,949,832 2,025,159 — — 2,025,159 Personal 839,958 864,904 — — 864,904 Total loans 16,989,660 17,178,060 — — 17,178,060 Allowance for loan losses (246,159 ) — — — — Loans, net of allowance 16,743,501 17,178,060 — — 17,178,060 Mortgage servicing rights 247,073 247,073 — — 247,073 Derivative instruments with positive fair value, net of cash margin 689,872 689,872 7,541 682,331 — Deposits with no stated maturity 20,526,295 20,526,295 — — 20,526,295 Time deposits 2,221,800 2,218,303 — — 2,218,303 Other borrowed funds 5,572,662 5,556,327 — — 5,556,327 Subordinated debentures 144,640 128,903 — 128,903 — Derivative instruments with negative fair value, net of cash margin 664,531 664,531 6,972 657,559 — Because no market exists for certain of these financial instruments and management does not intend to sell these financial instruments, the fair values shown in the tables above may not represent values at which the respective financial instruments could be sold individually or in the aggregate at the given reporting date. The following methods and assumptions were used in estimating the fair value of these financial instruments: Cash and Cash Equivalents The book value reported in the Consolidated Balance Sheets for cash and short-term instruments approximates those assets’ fair values. Securities The fair values of securities are generally based on Significant Other Observable Inputs such as quoted prices for comparable instruments or interest rates and credit spreads, yield curves, volatilities, prepayment speeds and loss severities. Loans The fair value of loans, excluding loans held for sale, are based on discounted cash flow analyses using interest rates and credit and liquidity spreads currently being offered for loans with similar remaining terms to maturity and risk, adjusted for the impact of interest rate floors and ceilings which are classified as Significant Unobservable Inputs. The fair values of loans were estimated to approximate their discounted cash flows less loan loss allowances allocated to these loans of $208 million at December 31, 2017 and $218 million at December 31, 2016 . A summary of assumptions used in determining the fair value of loans follows: Range of Average Discount December 31, 2017 Commercial 0.38% - 30.00% 0.64 0.77% - 4.67% Commercial real estate 0.38% - 18.00% 0.80 1.04% - 4.41% Residential mortgage 1.74% - 18.00% 2.27 2.11% - 4.09% Personal 1.18% - 21.00% 0.23 0.56% - 4.81% December 31, 2016 Commercial 0.38% - 30.00% 0.70 0.64% - 4.60% Commercial real estate 0.38% - 18.00% 0.71 0.94% - 4.27% Residential mortgage 1.74% - 18.00% 2.27 1.71% - 4.26% Personal 0.25% - 21.00% 0.40 1.03% - 4.59% Deposits The fair values of time deposits are based on discounted cash flow analyses using interest rates currently being offered on similar transactions which are considered Significant Unobservable Inputs. Estimated fair value of deposits with no stated maturity, which includes demand deposits, transaction deposits, money market deposits and savings accounts, is equal to the amount payable on demand. Although market premiums paid reflect an additional value for these low cost deposits, adjusting fair value for the expected benefit of these deposits is prohibited. Accordingly, the positive effect of such deposits is not included in the tables above. A summary of assumptions used in determining the fair value of time deposits follows: Range of Average Discount December 31, 2017 0.03% - 9.64% 1.91 2.18% - 2.36% December 31, 2016 0.02% - 9.65% 1.96 1.57% - 2.00% Other Borrowed Funds and Subordinated Debentures The fair values of these instruments are based upon discounted cash flow analyses using interest rates currently being offered on similar instruments which are considered Significant Unobservable Inputs. A summary of assumptions used in determining the fair value of other borrowings and subordinated debentures follows: Range of Average Discount December 31, 2017 Other borrowed funds 0.25% - 3.49% 0.00 1.33% - 4.04% Subordinated debentures 5.38% 16.79 4.61% December 31, 2016 Other borrowed funds 0.25% - 3.50% 0.00 0.55% - 3.22% Subordinated debentures 5.38% 16.86 6.11% Off-Balance Sheet Instruments The fair values of commercial loan commitments are based on fees currently charged to enter into similar agreements, taking into account the remaining terms of the agreements. The fair values of these off-balance sheet instruments were not significant at December 31, 2017 or December 31, 2016 . Fair Value Election As more fully disclosed in Note 2 and Note 7 to the Consolidated Financial Statements, the Company has elected to carry all U.S. government agency residential mortgage-backed securities held as economic hedges against changes in the fair value of mortgage servicing rights and all residential mortgage loans originated for sale at fair value. Changes in the fair value of these financial instruments are recognized in earnings.

Parent Company Only Financial S

Parent Company Only Financial Statements Parent Company Only Financial Statements	12 Months Ended
	Dec. 31, 2017
Condensed Financial Information of Parent Company Only Disclosure [Abstract]
Condensed Financial Information of Parent Company Only Disclosure [Text Block]	Parent Company Only Financial Statements Summarized financial information for BOK Financial – Parent Company Only follows: Balance Sheets (In thousands) December 31, 2017 2016 Assets Cash and cash equivalents $ 205,876 $ 163,418 Available for sale securities 16,185 19,234 Investment in bank subsidiaries 3,255,912 3,067,595 Investment in non-bank subsidiaries 170,966 177,068 Other assets 4,065 4,865 Total assets $ 3,653,004 $ 3,432,180 Liabilities and Shareholders’ Equity Liabilities: Other liabilities $ 12,960 $ 5,469 Other borrowings – Trust preferred debt — 7,217 Subordinated debentures 144,677 144,640 Total liabilities 157,637 157,326 Shareholders’ equity: Common stock 4 4 Capital surplus 1,035,895 1,006,535 Retained earnings 3,048,487 2,823,334 Treasury stock (552,845 ) (544,052 ) Accumulated other comprehensive loss (36,174 ) (10,967 ) Total shareholders’ equity 3,495,367 3,274,854 Total liabilities and shareholders’ equity $ 3,653,004 $ 3,432,180 Statements of Earnings (In thousands) Year Ended December 31, 2017 2016 2015 Dividends, interest and fees received from bank subsidiaries $ 150,149 $ 15,237 $ 150,308 Dividends, interest and fees received from non-bank subsidiaries 17,500 25,923 — Other revenue 936 1,612 1,279 Total revenue 168,585 42,772 151,587 Interest expense 8,239 4,182 131 Other operating expense 2,014 1,978 2,242 Total expense 10,253 6,160 2,373 Income before taxes and equity in undistributed income of subsidiaries 158,332 36,612 149,214 Federal and state income taxes (4,305 ) (1,920 ) (375 ) Income before equity in undistributed income of subsidiaries 162,637 38,532 149,589 Equity in undistributed income of bank subsidiaries 181,552 216,120 134,045 Equity in undistributed income of non-bank subsidiaries (9,545 ) (21,984 ) 4,931 Net income attributable to BOK Financial Corp. shareholders $ 334,644 $ 232,668 $ 288,565 Statements of Cash Flows (In thousands) Year Ended December 31, 2017 2016 2015 Cash Flows From Operating Activities: Net income $ 334,644 $ 232,668 $ 288,565 Adjustments to reconcile net income to net cash provided by operating activities: Equity in undistributed income of bank subsidiaries (181,552 ) (216,120 ) (134,045 ) Equity in undistributed income of non-bank subsidiaries 9,545 21,984 (4,931 ) Change in other assets 12 (2,933 ) 49 Change in other liabilities 7,457 (1,285 ) (2,818 ) Net cash provided by operating activities 170,106 34,314 146,820 Cash Flows From Investing Activities: Proceeds from sales of available for sale securities 3,000 1,632 4,760 Investment in subsidiaries (4,355 ) (26,000 ) (41,969 ) Acquisitions, net of cash acquired — (105,520 ) — Net cash used in investing activities (1,355 ) (129,888 ) (37,209 ) Cash Flows From Financing Activities: Net change in other borrowings (7,217 ) — — Issuance of subordinated debentures, net of issuance costs — 144,615 — Issuance of common and treasury stock, net 4,368 12,455 6,711 Dividends paid (116,041 ) (113,455 ) (115,281 ) Repurchase of common stock (7,403 ) (66,792 ) (229,540 ) Net cash used in financing activities (126,293 ) (23,177 ) (338,110 ) Net increase (decrease) in cash and cash equivalents 42,458 (118,751 ) (228,499 ) Cash and cash equivalents at beginning of period 163,418 282,169 510,668 Cash and cash equivalents at end of period $ 205,876 $ 163,418 $ 282,169 Cash paid for interest $ 6,211 $ 4,127 $ 131

Subsequent Events

Subsequent Events	12 Months Ended
	Dec. 31, 2017
Subsequent Events [Abstract]
Subsequent Events [Text Block]	Subsequent Events The Company evaluated events from the date of the Consolidated Financial Statements on December 31, 2017 through the issuance of those consolidated financial statements included in this Annual Report on Form 10-K. No events were identified requiring recognition in and/or disclosure in the Consolidated Financial Statements.

Significant Accounting Polici28

Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Basis of Presentation [Policy Text Block]	The Consolidated Financial Statements of BOK Financial Corporation (“BOK Financial” or “the Company”) have been prepared in conformity with accounting principles generally accepted in the United States ("U.S. GAAP"), including interpretations of U.S. GAAP issued by federal banking regulators and general practices of the banking industry.
Consolidation [Policy Text Block]	The Consolidated Financial Statements include the accounts of BOK Financial and its subsidiaries, principally BOKF, NA, BOK Financial Securities, Inc., The Milestone Group, Inc. and Cavanal Hill Distributors, Inc. All significant intercompany transactions are eliminated in consolidation. The Consolidated Financial Statements include the assets, liabilities, non-controlling interests and results of operations of variable interest entities (“VIEs”) when BOK Financial is determined to be the primary beneficiary. Variable interest entities are generally defined as entities that either do not have sufficient equity to finance their activities without support from other parties or whose equity investors lack a controlling financial interest. See additional discussion of variable interest entities at Note 14 following.
Reclassifications [Text Block]	Certain prior year amounts have been reclassified to conform to current year presentation. Check card revenue of $19.3 million in 2016 and $19.0 million in 2015 were reclassified from transaction card revenue to deposit service charges and fees
Nature of Operations [Text Block]	Nature of Operations BOK Financial, through its subsidiaries, provides a wide range of financial services to commercial and industrial customers, other financial institutions, municipalities, and consumers. These services include depository and cash management; lending and lease financing; mortgage banking; securities brokerage, trading and underwriting; and personal and corporate trust. BOKF, NA ("the Bank") operates as Bank of Oklahoma primarily in the Tulsa and Oklahoma City metropolitan areas of the state of Oklahoma and Bank of Texas primarily in the Dallas, Fort Worth and Houston metropolitan areas of the state of Texas. In addition, BOKF, NA does business as Bank of Albuquerque in Albuquerque, New Mexico; Colorado State Bank and Trust in Denver, Colorado; Bank of Arizona in Phoenix, Arizona; Mobank in Kansas City, Missouri/Kansas and Bank of Arkansas in Northwest Arkansas. BOKF, NA also operates the TransFund electronic funds network, Cavanal Hill Investment Management, and BOK Financial Asset Management, Inc.
Use of Estimates [Policy Text Block]	Use of Estimates Preparation of BOK Financial's Consolidated Financial Statements requires management to make estimates of future economic activities, including loan collectability, prepayments and cash flows from customer accounts. These estimates are based upon current conditions and information available to management. Actual results may differ significantly from these estimates.
Acquisitions [Policy Text Block]	Acquisitions Assets and liabilities acquired, including identifiable intangible assets, are recorded at fair value on the acquisition date. The purchase price includes consideration paid at closing and the estimated fair value of contingent consideration that will be paid in the future, subject to achieving defined performance criteria. Premiums and discounts assigned to interest-earning assets and interest-bearing liabilities are amortized over the lives of the acquired assets and liabilities on either an individual instrument or pool basis. Provision for credit losses is recognized for changes in credit quality after the acquisition date. Goodwill is recognized as the excess of the purchase price over the net fair value of assets acquired and liabilities assumed. The Consolidated Statements of Earnings include the results of operations from the acquisition date.
Goodwill and Intangible Assets [Policy Text Block]	Goodwill and Intangible Assets Goodwill and intangible assets generally result from business combinations and are evaluated for each of BOK Financial's reporting units for impairment annually or more frequently if conditions indicate impairment. The evaluation of possible impairment of goodwill and intangible assets involves significant judgment based upon short-term and long-term projections of future performance. Reporting units are defined by the Company as significant lines of business within each operating segment. This definition is consistent with the manner in which the chief operating decision maker assesses the performance of the Company and makes decisions concerning the allocation of resources. The Company qualitatively assesses whether it is more likely than not that the fair value of the reporting units are less than their carrying value, including goodwill. Reporting unit carrying value includes sufficient capital to exceed regulatory requirements. This assessment includes consideration of relevant events and circumstances including but not limited to macroeconomic conditions, industry and market conditions, the financial and stock performance of the Company and other relevant factors. If the Company concludes based on the qualitative assessment that goodwill may be impaired, a quantitative one-step impairment test will be applied to goodwill at all reporting units. The quantitative analysis compares the fair value of the reporting unit with its carrying value, including goodwill. The fair value of each reporting unit is estimated by the discounted future earnings method. Goodwill is considered impaired if the fair value of the reporting unit is less than the carrying value of the reporting unit, including goodwill. Intangible assets are generally composed of customer relationships, naming rights, non-compete agreements and core deposit premiums. They are amortized using accelerated or straight-line methods, as appropriate, over the estimated benefit periods. These periods range from 3 years to 20 years . The net book values of identifiable intangible assets are evaluated for impairment when economic conditions indicate impairment may exist.
Cash and Cash Equivalents [Policy Text Block]	Cash Equivalents Due from banks, funds sold (generally federal funds sold for one day), resell agreements (which generally mature within one to 30 days ) and investments in money market funds are considered cash equivalents.
Securities [Policy Text Block]	Securities Securities are identified as trading, investment (held to maturity) or available for sale at the time of purchase based upon the intent of management, liquidity and capital requirements, regulatory limitations and other relevant factors. Trading securities, which are acquired for profit through resale, are carried at fair value with unrealized gains and losses included in current period earnings. Investment securities are carried at amortized cost. Amortization is computed by methods that approximate level yield and is adjusted for changes in prepayment estimates. Securities identified as available for sale are carried at fair value. Unrealized gains and losses are recorded, net of deferred income taxes, as accumulated other comprehensive income in shareholders' equity. Available for sale securities are separately identified as pledged to creditors if the creditor has the right to sell or re-pledge the collateral. The purchase or sale of securities is recognized on a trade date basis. Realized gains and losses on sales of securities are based upon specific identification of the security sold. A receivable or payable is recognized for subsequent transaction settlement. Securities meeting certain criteria may also be transferred from the available for sale classification to the investment securities portfolio at fair value on the date of transfer. The unrealized gain or loss at the date of transfer is retained in accumulated other comprehensive income and in the carrying value of the investment securities portfolio. Such amounts are amortized over the estimated remaining life of the security as an adjustment to yield, offsetting the related amortization of the premium or accretion of the discount on the transferred securities. On a quarterly basis, the Company performs separate evaluations of impaired debt investment and available for sale securities and equity available for sale securities to determine if the decline in fair value below the amortized cost is other-than-temporary. For debt securities, management determines whether it intends to sell or if it is more likely than not that it will be required to sell impaired securities. This determination considers current and forecasted liquidity requirements and securities portfolio management. If the Company intends to sell or it is more likely than not that it will be required to sell the impaired debt security, a charge is recognized against earnings for the entire unrealized loss. For all impaired debt securities for which there is no intent or expected requirement to sell, the evaluation considers all available evidence to assess whether it is more likely than not that all amounts due would not be collected according to the security's contractual terms. Impairment of debt securities rated investment grade by all nationally-recognized rating agencies is considered temporary unless specific contrary information is identified. Impairment of debt securities rated below investment grade by at least one of the nationally recognized rating agencies is evaluated based on projections of estimated cash flows. Any expected credit loss due to the inability to collect all amounts due according to the security's contractual terms is recognized as a charge against earnings. Any remaining unrealized loss related to other factors would be recognized in other comprehensive income, net of taxes. For equity securities, management evaluates various factors including cause, severity and duration of the decline in value of the security and prospects for recovery, as well as the Company's intent and ability not to sell the security until the fair value exceeds amortized cost. If an unrealized loss is determined to be other-than-temporary, a charge is recognized against earnings for the difference between the security's amortized cost and fair value. BOK Financial may elect to carry certain securities at fair value with changes in fair value recognized in current period income. These securities are held with the intent that gains or losses will offset changes in the fair value of mortgage servicing rights or certain derivative instruments. Restricted equity securities represent equity interests the Company is required to hold in the Federal Reserve Banks and Federal Home Loan Banks. Restricted equity securities are carried at cost as these securities do not have a readily determined fair value because ownership of these shares is restricted and they lack a market.
Derivatives Instruments [Policy Text Block]	Derivative Instruments Derivative instruments may be used by the Company as part of its internal risk management programs or may be offered to customers. All derivative instruments are carried at fair value and changes in fair value are generally reported in income as they occur. The determination of fair value of derivative instruments considers changes in interest rates, commodity prices and foreign exchange rates. Credit risk is also considered in determining fair value. Deterioration in the credit rating of customers or other counterparties reduces the fair value of asset contracts. Deterioration of our credit rating could decrease the fair value of our derivative liabilities. When bilateral netting agreements or similar agreements exist between the Company and its counterparties that create a single legal claim or obligation to pay or receive the net amount in settlement of the individual derivative contracts, the Company reports derivative assets and liabilities on a net by derivative contract by counterparty basis. Derivative contracts may also require the Company to provide or receive cash margin as collateral for derivative assets and liabilities. Derivative assets and liabilities are reported net of cash margin when certain conditions are met. In addition, derivative contracts executed with customers under Customer Risk Management Programs may be secured by non-cash collateral in conjunction with a credit agreement with that customer. Access to collateral in the event of default is reasonably assured. Derivative instruments may be designated as cash flow hedges of variable rate assets or liabilities, or of anticipated transactions. Changes in the fair value of derivative instruments designated as cash flow hedges are recorded in accumulated other comprehensive income to the extent they are effective. The amount recorded in other comprehensive income is reclassified to earnings in the same periods as the hedged cash flows impact earnings. The ineffective portion of changes in fair value is reported in current earnings. BOK Financial may use derivative instruments in managing its interest rate sensitivity, as part of its economic hedge of the changes in the fair value of mortgage servicing rights and to mitigate the market risk of holding trading securities. Changes in the fair value of derivative instruments used in managing interest rate sensitivity and as part of its economic hedge of changes in the fair value of mortgage servicing rights are included in Other Operating Revenue - Gain (loss) on derivatives, net in the Consolidated Statements of Earnings. Changes in the fair value of derivative instruments used to mitigate the market risk of holding trading securities are included in Operating Revenue - Brokerage and trading revenue. BOK Financial also enters into mortgage loan commitments that are considered derivative contracts. Forward sales contracts that have not been designated as hedging instruments are used to economically hedge these mortgage loan commitments as well as mortgage loans held for sale. Mortgage loan commitments are carried at fair value based upon quoted prices. Changes in the fair value of mortgage loan commitments, mortgage loans held for sale and forward sales contracts are reported in Other Operating Revenue - Mortgage Banking Revenue. BOK Financial offers programs that permit its customers to manage various risks, including fluctuations in energy, cattle and other agricultural products, interest rates and foreign exchange rates with derivative contracts. Customers may also manage interest rate risk through interest rate swaps used by the borrower to modify interest rate terms of their loans or to-be-announced securities used by our mortgage banking customers to hedge their loan production. Derivative contracts are executed between the customers and BOK Financial. Offsetting contracts are executed between BOK Financial and other selected counterparties to minimize market risk from changes in commodity prices, interest rates or foreign exchange rates. The counterparty contracts are identical to customer contracts, except for a fixed pricing spread or fee paid to BOK Financial as profit and compensation for administrative costs and credit risk which is recognized over the life of the contracts and included in other Operating Revenue - Brokerage and Trading Revenue in the Consolidated Statements of Earnings.
Loans [Policy Text Block]	Loans Loans are either secured or unsecured based on the type of loan and the financial condition of the borrower. Repayment is generally expected from cash flow or proceeds from the sale of selected assets of the borrower. BOK Financial is exposed to risk of loss on loans due to the borrower's financial difficulties, which may arise from any number of factors, including problems within the respective industry or local economic conditions. Access to collateral, in the event of borrower default, is reasonably assured through adherence to applicable lending laws and through sound lending standards and credit review procedures. Accounting policies for all loans, excluding residential loans guaranteed by U.S. government agencies, are as follows. Interest is accrued at the applicable interest rate on the outstanding principal amount. Loans are placed on nonaccruing status when, in the opinion of management, full collection of principal or interest is uncertain. Internally risk graded loans are individually evaluated for nonaccruing status quarterly. Non-risk graded loans are generally placed on nonaccruing status when 90 days or more past due or within 60 days of being notified of the borrower's bankruptcy filing. Interest previously accrued but not collected is charged against interest income when the loan is placed on nonaccruing status. Payments received on nonaccruing loans are applied to principal or recognized as interest income, according to management's judgment as to the collectability of principal. Loans may be returned to accruing status when, in the opinion of management, full collection of principal and interest, including principal previously charged off, is probable based on improvements in the borrower's financial condition or a sustained period of performance. Loans to borrowers experiencing financial difficulties may be modified in troubled debt restructurings ("TDRs"). All TDRs are classified as nonaccruing. Modifications generally consist of extension of payment terms or interest rate concessions and may result either voluntarily through negotiations with the borrower or involuntarily through court order. Generally, principal and accrued but unpaid interest is not voluntarily forgiven. Performing loans may be renewed under the current collateral, debt service ratio and other underwriting standards. Nonaccruing loans may also be renewed and will remain classified as nonaccruing. Occasionally, loans, other than residential mortgage loans, may be held for sale in order to manage credit concentration. These loans are carried at the lower of cost or fair value with gains or losses recognized in gain (loss) on assets. All loans are charged-off when the loan balance or a portion of the loan balance is no longer supported by the paying capacity of the borrower or when the required cash flow is reduced in a TDR. The charge-off amount is determined through an evaluation of available cash resources and collateral value. Internally risk graded loans are evaluated quarterly and charge-offs are taken in the quarter in which the loss is identified. Non-risk graded loans that are past due between 60 days and 180 days , based on the loan product type, are charged off. Loans to borrowers whose personal obligation has been discharged through Chapter 7 bankruptcy proceedings are charged off within 60 days of notice of the bankruptcy filing, regardless of payment status. Loan origination and commitment fees and direct loan acquisition and origination costs are deferred and amortized as an adjustment to yield over the life of the loan or over the commitment period, as applicable. Amortization does not anticipate loan prepayments. Net unamortized fees are recognized in full at time of payoff. Qualifying residential mortgage loans guaranteed by U.S. government agencies have been sold into GNMA pools. Under certain performance conditions specified in government programs, the Company has the right, but not the obligation to repurchase loans from GNMA pools. These loans no longer qualify for sale accounting and are recognized in the Consolidated Balance Sheet. Guaranteed loans are considered to be impaired because we do not expect to receive all principal and interest based on the loan's contractual terms. The principal balance continues to be guaranteed, however, interest accrues at a curtailed rate as specified in the programs. The carrying value of these loans is reduced based on an estimate of expected cash flows discounted at the original note rate plus a liquidity spread. Guaranteed loans may be modified in TDRs in accordance with U.S. government agency guidelines. Interest continues to accrue at the modified rate. U.S. government guaranteed loans may either be resold into GNMA pools after a performance period specified by the programs or foreclosed and conveyed to the guarantors. Loans are disaggregated into portfolio segments and further disaggregated into classes. The portfolio segment is the level at which the Company develops and documents a systematic method for determining its Allowance for Credits Losses. Classes are based on the risk characteristics of the loans and the Company's method for monitoring and assessing credit risk.
Allowance for Loan Losses and Accrual for Off-Balance Sheet Credit Losses [Policy Text Block]	Allowance for Loan Losses and Accrual for Off-Balance Sheet Credit Risk The appropriateness of the allowance for loan losses and accrual for off-balance sheet credit risk (collectively "Allowance for Credit Losses") is assessed by management quarterly based on an ongoing quarterly evaluation of the probable estimated losses inherent in the portfolio, including probable losses on outstanding loans and unused commitments to provide financing. A consistent well-documented methodology has been developed and is applied by an independent Credit Administration department to assure consistency across the Company. The allowance for loan losses consists of specific allowances attributed to impaired loans that have not yet been charged down to amounts we expect to recover, general allowances based on estimated loss rates by loan class and nonspecific allowances based on factors that affect more than one portfolio segment. There were no changes to the methodology for estimating general allowances during 2017 or 2016 . Loans are considered to be impaired when it becomes probable that BOK Financial will be unable to collect all amounts due according to the contractual terms of the loan agreements. Internally risk graded loans are evaluated individually for impairment. Substantially all commercial and commercial real estate loans and certain residential mortgage and personal loans are risk graded based on a quarterly evaluation of the borrowers' ability to repay. Certain commercial loans and most residential mortgage and personal loans are small balance, homogeneous pools of loans that are not risk graded. Non-risk graded loans are identified as impaired based on performance status. Generally, non-risk graded loans 90 days or more past due, modified in a troubled debt restructuring or in bankruptcy are considered to be impaired. Specific allowances for impaired loans are measured by an evaluation of estimated future cash flows discounted at the loan's initial effective interest rate or the fair value of collateral for certain collateral dependent loans. The fair value of real property held as collateral is generally based on third party appraisals that conform to Uniform Standards of Professional Appraisal Practice, less estimated selling costs. Appraised values are on an “as-is” basis and generally are not adjusted by the Company. Updated appraisals are obtained at least annually or more frequently if market conditions indicate collateral values may have declined. Collateral value of mineral rights is generally determined by our internal staff of engineers based on projected cash flows from proven oil and gas reserves under existing economic and operating conditions. The value of other collateral is generally determined by our special assets staff based on projected liquidation cash flows under current market conditions. Collateral values and available cash resources that support impaired loans are evaluated quarterly. Historical statistics may be used as a practical way to estimate impairment in limited situations, such as when a collateral dependent loan is identified as impaired at the end of a reporting period until an appraisal of collateral value is received or a full assessment of future cash flows is completed. Estimates of future cash flows and collateral values require significant judgments and may be volatile. General allowances for unimpaired loans are based on an estimated loss rate by loan class. The appropriate historical gross loss rate for each loan class is determined by the greater of the current loss rate based on the most recent twelve months or a ten-year average gross loss rate. Recoveries are not directly considered in the estimation of historical loss rates. Recoveries generally do not follow predictable patterns and are not received until well-after the charge-off date as a result of protracted legal actions. For risk graded loans, historical gross loss rates are adjusted for changes in risk grading. For each loan class, the current weighted average risk grade is compared to the long-term weighted average risk grade. This comparison determines whether credit risk in each loan class is increasing or decreasing. Historical loss rates are adjusted upward or downward in proportion to changes in average risk grading. General allowances for unimpaired loans also consider inherent risks identified for each loan class. Inherent risks consider loss rates that most appropriately represent the current credit cycle and other factors attributable to a specific loan class which have not yet been represented in the historical gross loss rates or risk grading. These factors include changes in commodity prices or engineering imprecision which may affect the value of reserves that secure our energy loan portfolio, construction risk that may affect commercial real estate loans, changes in regulations and public policy that may disproportionately impact health care loans and changes in loan products. Nonspecific allowances are maintained for risks beyond factors specific to a particular portfolio segment or loan class. These factors include trends in the economy in our primary lending areas, concentration in large-balance loans and other relevant factors. An accrual for off-balance sheet credit risk is included in Other liabilities. The appropriateness of the accrual is determined in the same manner as the allowance for loan losses. A provision for credit losses is charged against or credited to earnings in amounts necessary to maintain an appropriate Allowance for Credit Losses. Recoveries of loans previously charged off are added to the allowance when received.
Real Estate and Other Repossessed Assets [Policy Text Block]	Real Estate and Other Repossessed Assets Real estate and other repossessed assets are acquired in partial or total forgiveness of loans. These assets are initially recognized at cost, which is determined by fair value at date of foreclosure less estimated disposal costs. They are subsequently carried at the lower of cost or current fair value less estimated disposal costs. Decreases in fair value below cost are recognized as asset-specific valuation allowances which may be reversed when supported by future increases in fair value. Subsequent increases in fair value may be used to reduce the allowance but not below zero. Fair values of real estate are based on “as is” appraisals which are updated at least annually or more frequently for certain asset types or assets located in certain distressed markets. Fair values based on appraisals are generally considered to be based on significant other observable inputs. The Company also considers decreases in listing price and other relevant information in quarterly evaluations and reduces the carrying value of real estate and other repossessed assets when necessary. Fair values based on list prices and other relevant information are generally considered to be based on significant unobservable inputs. Additional costs incurred to complete real estate and other repossessed assets may increase the carrying value, up to current fair value based on “as completed” appraisals. The fair value of mineral rights included in repossessed assets are generally determined by our internal staff of engineers based on projected cash flows from proven oil and gas reserves under existing economic and operating conditions. The value of other repossessed assets is generally determined by our special assets staff based on projected liquidation cash flows under current market conditions. Income generated by these assets is recognized as received. Operating expenses are recognized as incurred. Gains or losses on sales of real estate and other repossessed assets are based on the cash proceeds received less the cost basis of the asset, net of any valuation allowances. The estimated disposal costs of real estate and other repossessed assets are evaluated by the Company on an annual basis based on actual results.
Transfers of Financial Assets [Policy Text Block]	Transfers of Financial Assets BOK Financial regularly transfers financial assets as part of its mortgage banking activities and periodically may transfer other financial assets. Transfers are recorded as sales when the criteria for surrender of control are met. The Company has elected to carry certain residential mortgage loans held for sale at fair value under the fair value option. Changes in fair value are recognized in net income as they occur. These loans are reported separately in the Consolidated Balance Sheets and changes in fair value are recorded in other operating revenue - mortgage banking revenue in the Consolidated Statements of Earnings. Fair value of conforming residential mortgage loans that will be sold to U.S. government agencies is based on sales commitments or market quotes considered Level 2 inputs. Fair value of mortgage loans that are unable to be sold to U.S. government agencies is based on Level 3 inputs using quoted prices of loans that are sold in securitization transactions with a liquidity discount applied. The fair value is corroborated with an independent third party on at least an annual basis. BOK Financial retains a repurchase obligation under underwriting representations and warranties related to residential mortgage loans transferred and generally retains the right to service the loans. The Company may incur a recourse obligation in limited circumstances. Separate accruals are recognized in Other liabilities in the Consolidated Balance Sheets for repurchase and recourse obligations. These reserves reflect the estimated amount of probable loss the Company will incur as a result of repurchasing a loan, indemnifications, and other settlement resolutions. Repurchases of loans with an origination defect that are also credit impaired are considered collateral dependent and are initially recognized at net realizable value (appraised value less the cost to sell). The difference between unpaid principal balance and net realizable value is not accreted. Repurchases of loans with an origination defect that are not credit impaired are carried at fair value as of the repurchase date. Interest income continues to accrue on these loans and the discount is accreted over the estimated life of the loan. The Company may also choose to purchase GNMA loans once certain mandated delinquency criteria are met. The loans that are eligible and are chosen to be repurchased are initially recognized at fair value based on expected cash flow discounted using the average agency guaranteed debenture rates, average actual principal loss rates and liquidity premium.
Mortgage Servicing Rights [Policy Text Block]	Mortgage Servicing Rights Mortgage servicing rights may be purchased or may be recognized when mortgage loans are originated and sold with servicing rights retained. All mortgage servicing rights are carried at fair value. Changes in the fair value are recognized in earnings as they occur. Mortgage servicing rights are not traded in active markets. A cash flow model is used to determine fair value. Key assumptions and estimates, including projected prepayment speeds and assumed servicing costs, earnings on escrow deposits, ancillary income and discount rates, used by this model are based on current market sources. Assumptions used to value mortgage servicing rights are considered significant unobservable inputs. A separate third party model is used to estimate prepayment speeds based on interest rates, housing turnover rates, estimated loan curtailment, anticipated defaults and other relevant factors. The prepayment model is updated daily for changes in market conditions and adjusted to better correlate with actual performance of BOK Financial's servicing portfolio. Fair value estimates from outside sources are received at least annually to corroborate the results of the valuation model.
Premises and Equipment [Policy Text Block]	Premises and Equipment Premises and equipment are carried at cost, including capitalized interest when appropriate, less accumulated depreciation and amortization. Depreciation and amortization are computed on a straight-line basis over the estimated useful lives of the assets or, for leasehold improvements, over the shorter of the estimated useful lives or remaining lease terms. Useful lives range from 5 years to 40 years for buildings and improvements, 3 years to 10 years for software and 3 years to 10 years for furniture and equipment. Construction in progress represents facilities construction and data processing systems projects underway that have not yet been placed into service. Depreciation and amortization begin once the assets are placed into service. Repair and maintenance costs, including software maintenance and enhancement costs, are charged to expense as incurred. Software licensing costs are generally charged to expense as incurred. Software licensing costs are capitalized if the contractual right to take possession of the software exists and it is feasible to take possession without significant penalty. Capitalized costs are amortized over the shorter of the estimated useful life of the software or remaining contractual life of the license. Premises no longer used by the Company are transferred to real estate and other repossessed assets. The transferred amount is the lower of cost less accumulated depreciation or fair value less estimated disposal costs as of the transfer date. Rent expense for leased premises is recognized as incurred over the lease term. The effects of rent holidays, significant rent escalations and other adjustments to rent payments are recognized on a straight-line basis over the lease term. Ongoing technology projects of significant size or length are reviewed at least annually for impairment. Accumulated costs are reviewed for projects or components of projects that do not support the value of the asset being developed. Findings of obsolescence, duplicate effort or other conditions that do not support the recorded value are impaired, with the cost of the impaired components being charged to current-year earnings.
Federal and State Income Taxes [Policy Text Block]	Federal and State Income Taxes BOK Financial and its subsidiaries file consolidated tax returns. The subsidiaries provide for income taxes on a separate return basis and remit to BOK Financial amounts determined to be currently payable. BOK Financial is agent for its subsidiaries under the Company's tax sharing agreements and has no ownership rights to any refunds received for the benefit of its subsidiaries. Current income tax expense or benefit is based on an evaluation that considers estimated taxable income, tax credits, and statutory federal and state income tax rates. The amount of current income tax expense or benefit recognized in any period may differ from amounts reported to taxing authorities. Annually, tax returns are filed with each jurisdiction where the Company conducts business and recognized current income tax expense or benefit is adjusted to the filed tax returns. Deferred tax assets and liabilities are based upon the temporary differences between the values of assets and liabilities as recognized in the financial statements and their related tax basis using enacted tax rates in effect for the year in which the differences are expected to be recovered or settled. The effect of changes in statutory tax rates on the measurement of deferred tax assets and liabilities is recognized through income tax expense in the period the change is enacted. A valuation allowance is provided when it is more likely than not that some portion of the entire deferred tax asset may not be realized. BOK Financial has unrecognized tax benefits, which are included in accrued current income taxes payable, for the uncertain portion of recorded tax benefits and related interest. These uncertainties result from the application of complex tax laws, rules, regulations and interpretations, primarily in state taxing jurisdictions. Unrecognized tax benefits are assessed quarterly and may be adjusted through current income tax expense in future periods based on changing facts and circumstances, completion of examinations by taxing authorities or expiration of a statute of limitations. Estimated penalties and interest on uncertain tax positions are recognized in income tax expense.
Employee Benefit Plans [Policy Text Block]	Employee Benefit Plans BOK Financial sponsors a defined benefit cash balance pension plan (“Pension Plan”), a defined contribution plan (“Thrift Plan”) and employee health care plans. Pension Plan costs, which are based upon actuarial computations of current costs, are expensed annually. Unrecognized prior service cost and net gains or losses are amortized on a straight-line basis over a period not to exceed the average remaining service periods of the participants. Employer contributions to the Pension Plan are in accordance with Federal income tax regulations. Pension Plan benefits were curtailed as of April 1, 2006. No participants may be added to the Pension Plan and no additional service benefits will be accrued. BOK Financial recognizes the funded status of its employee benefit plans. For a pension plan, the funded status is the difference between the fair value of plan assets and the projected benefit obligation measured as of the fiscal year-end date. Adjustments required to recognize the Pension Plan's net funded status are made through accumulated other comprehensive income, net of deferred income taxes. Employer contributions to the Thrift Plan, which matches employee contributions subject to percentage and years of service limits, are expensed when incurred. BOK Financial recognizes the expense of health care benefits on the accrual method.
Shared-Based Compensation Plans [Policy Text Block]	Share-Based Compensation Plans BOK Financial awards stock options and non-vested common shares as compensation to certain officers. Compensation cost is generally fixed based on the grant date fair value of the award. The grant date fair value of stock options is based on the Black-Scholes option pricing model. Stock options generally have graded vesting over 7 years . Each tranche is considered a separate award for valuation and compensation cost recognition. Grant date fair value of non-vested shares is based on the then-current market value of BOK Financial common stock. Non-vested shares awarded since January 1, 2013 generally cliff vest in 3 years and are subject to a two year holding period after vesting. Shares awarded under the Executive Incentive Plan are subject to downward adjustment at the discretion of the Incentive Compensation Committee. Compensation cost of non-vested shares granted under the Executive Incentive Plan varies based on changes in the fair value of BOKF common shares. Compensation cost is recognized as expense over the service period, which is generally the vesting period. Expense is reduced for estimated forfeitures over the vesting period and adjusted for actual forfeitures as they occur. Stock-based compensation awarded to certain officers has performance conditions that affect the number of awards granted. Compensation cost is adjusted based on the probable outcome of the performance conditions. Tax effects of share-based payments are recognized through tax expense. Dividends on non-vested shares that are not subject to forfeiture are charged to retained earnings..
Other Operating Revenue [Policy Text Block]	Other Operating Revenue Fees and commission revenue is recognized at the time the related services are provided or products are sold and may be accrued when appropriate. Accrued fees and commissions are reversed against revenue if amounts are subsequently deemed to be uncollectible. Revenue is recognized on a gross basis whenever we have primary responsibility and risk in providing the services or products to our customers and on a net basis whenever we act as an agent for products or services of others. Brokerage and trading revenue includes realized and unrealized gains and losses from securities and derivatives held for trading purposes and derivatives held for customer risk management programs, including credit losses, commissions earned from the retail sale of securities, mutual funds and other financial instruments, and underwriting and financial advisory fees. Transaction card revenue includes merchant discount fees and electronic funds transfer network fees. Merchant discount fees represent fees paid by customers for account management and electronic processing of transactions. Merchant discount fees are recognized at the time the customer's transactions are processed or other services are performed. The Company also maintains the TransFund electronic funds transfer network for the benefit of its members, which includes BOKF, NA. Electronic funds transfer fees are recognized as electronic transactions are processed on behalf of its members. Fiduciary and asset management revenue includes fees from asset management, custody, recordkeeping, investment advisory and administration services. Revenue is recognized on an accrual basis at the time the services are performed and may be based on either the fair value of the account or the service provided. Deposit service charges and fees are recognized at least quarterly in accordance with a published deposit account agreements and disclosure statements for retail accounts or contractual agreements for commercial accounts. Item charges for overdraft or non-sufficient funds items are recognized as items are presented for payment. Account balance charges and activity fees are accrued monthly and collected in arrears. Commercial account activity fees may be offset by an earnings credit based on account balances. Check card fees represent interchange fees paid by a merchant bank for transactions processed from cards issued by the Company. Check card fees are recognized when transactions are processed. Interchange fees are generally recognized on a gross basis. Related expenses are generally recognized as Data processing and communications expense.
Newly Adopted and Pending Accounting Pronouncements [Policy Text Block]	Newly Adopted and Pending Accounting Pronouncements The following is a summary of newly adopted and pending accounting pronouncements that may have a more than insignificant effect on the Company's financial statements. Financial Accounting Standards Board ("FASB") FASB Accounting Standards Update No. 2014-09, Revenue from Contracts with Customers ("ASU 2014-09") On May 28, 2014, the FASB issued ASU 2014-09 to clarify the principles for recognizing revenue by providing a more robust framework that will give greater consistency and comparability in revenue recognition practices. In the new framework, an entity recognizes revenue in an amount that reflects the consideration to which the entity expects to be entitled in exchange for goods or services. The new model requires the identification of performance obligations included in contracts with customers, a determination of the transaction price and an allocation of the price to those performance obligations. The entity recognizes revenue when performance obligations are satisfied. Revenue from financial assets and liabilities is explicitly excluded from the scope of ASU 2014-09. Management adopted the standard in the first quarter of 2018. There were no significant cumulative effect adjustments as a result of implementation as of January 1, 2018 as our current revenue recognition policies generally conform with the principals in ASU 2014-09. FASB Accounting Standards Update No. 2016-08, Revenue from Contracts with Customers (Topic 606): Principal versus Agent Considerations (Reporting Revenue Gross versus Net) ("ASU 2016-08") On March 17, 2016, the FASB Issued ASU 2016-08 to amend the principal versus agent implementation guidance in ASU 2014-09. The ASU clarifies that an entity should evaluate whether it is the principal or the agent for each specified good or service promised in a contract with a customer. ASU 2016-08 is effective for the Company for annual reporting periods beginning after December 15, 2017, including interim periods within that reporting period. Management expects that interchange fees paid to issuing banks for card transactions processed related to its merchant processing services currently included in data processing and communication expense, will be netted against the amounts charged to the merchant in transaction card processing revenue. For 2017, interchange fees related to merchant processing services were approximately $39 million . FASB Accounting Standards Update No. 2016-01, Financial Instruments - Overall (Subtopic 825-10): Recognition and Measurement of Financial Assets and Financial Liabilities ("ASU 2016-01") On January 5, 2016, the FASB issued ASU 2016-01 over the recognition and measurement of financial assets and liabilities. The update requires equity investments, in general, to be measured at fair value with changes in fair value recognized in earnings. It also eliminates the requirement to disclose the methods and significant assumptions used to estimate the fair value for financial instruments measured at amortized cost, requires entities to use the exit price notion when measuring fair value, requires an entity to present separately in other comprehensive income the portion of the total change in fair value of a liability resulting from a change in the instrument-specific credit risk when the fair value option has been elected, requires separate presentation of financial assets and liabilities by measurement category and form on the balance sheet or accompanying notes, clarifies that an entity should evaluate the need for a valuation allowance on a deferred tax asset related to available-for-sale securities in combination with the entity's other deferred tax assets, and simplifies the impairment assessment of equity investments without readily determinable fair values. The ASU is effective for the Company for interim and annual periods beginning after December 15, 2017. Upon adoption, unrealized gains and losses from equity securities will be reclassified from other comprehensive income to retained earnings. At December 31, 2017 , the Company had $2.7 million of net unrealized gains included in accumulated other comprehensive income. FASB Accounting Standards Update No. 2016-02, Leases (Topic 842) ("ASU 2016-02") On February 25, 2016, the FASB issued ASU 2016-02 to increase transparency and comparability by recognizing lease assets and liabilities on the balance sheet and disclosing key information about leasing arrangements. Lessees will be required to recognize an obligation for future lease payments measured on a discounted basis and a right-of-use asset. The ASU is effective for the Company for interim and annual periods beginning after December 15, 2018 and requires transition through a modified retrospective approach for leases existing at or entered into after January 1, 2017. The Company currently estimates that implementation of ASU 2016-02 will increase reported right of use assets and liabilities by approximately $100 million to $150 million . FASB Accounting Standards Update No. 2016-09, Compensation - Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting ("ASU 2016-09") On March 30, 2016, the FASB issued ASU 2016-09 to simplify multiple aspects of accounting for employee share-based payment transactions including accounting for income taxes, forfeitures, and statutory tax withholding requirements. The ASU became effective for annual reporting periods beginning after December 15, 2016, including interim periods within those annual reporting periods. Implementation of ASU 2016-09 decreased tax expense $2.8 million in 2017. FASB Accounting Standards Update No. 2016-13, Financial Instruments - Credit Losses (Topic 326): Assets Measured at Amortized Cost ("ASU 2016-13") On June 16, 2016, the FASB issued ASU 2016-13 in order to provide more timely recording of credit losses on loans and other financial instruments. The ASU adds an impairment model (known as the current expected credit loss ("CECL") model) that is based on expected credit losses rather than incurred credit losses. It requires measurement of all expected credit losses for financial assets carried at amortized cost, including loans and investment securities, based on historical experience, current conditions, and reasonable and supportable forecasts. ASU 2016-13 also changes the recognition of other-than-temporary impairment of available for sale securities to an allowance methodology from a direct write-down methodology. ASU 2016-13 will be effective for the Company for annual reporting periods beginning after December 15, 2019, including interim periods within those fiscal years. Early adoption is permitted for annual reporting periods beginning after December 15, 2018. ASU 2016-13 will be applied through a cumulative-effect adjustment to retained earnings as of the beginning of the first reporting period in which the guidance is effective. The Company is evaluating the impact the adoption of ASU 2016-13 will have on the Company's financial statements. FASB Accounting Standards Update No. 2016-15, Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments ("ASU 2016-15") On August 26, 2016, the FASB issued ASU 2016-15, which amends guidance in ASC 230 on the classification of certain cash receipts and payments in the statement of cash flows. The amendments address eight cash flow issues. ASU 2016-15 is effective for the Company for interim and annual reporting periods beginning after December 15, 2017. Entities generally must apply the guidance retrospectively to all periods presented. Adoption of ASU 2016-15 is not expected to have a material impact on the Company's financial statements. FASB Accounting Standards Update No. 2017-12, Derivatives and Hedging (Topic 815): Targeted Improvements to Accounting for Hedging Activities ("ASU 2017-12") On August 28, 2017, the FASB issued ASU 2017-12, which amends the hedge accounting recognition and presentation requirements in ASC 815 in order to improve transparency and understandability of information and reduce the complexity. The update expands the types of transactions eligible for hedge accounting, eliminates the requirement to separately measure and present hedge ineffectiveness, simplifies hedge effectiveness assessments and updates documentation and presentation requirements. The update allows the reclassification of certain debt securities from held to maturity to available for sale if the debt security is eligible to be hedged under the last-of-layer method. ASU 2017-12 is effective for the Company for fiscal years beginning after December 15, 2018, and interim periods therein; however, early adoption is permitted. The Company is evaluating the impact the adoption of ASU 2017-12 will have on the Company's financial statements. FASB Accounting Standards Update No. 2018-02, Income Statement - Reporting Comprehensive Income (Topic 220): Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income ("ASU 2018-02") On February 10, 2018, the FASB issued ASU 2018-02, which allows a reclassification from accumulated other comprehensive income to retained earnings for the tax effect of temporary differences originated through comprehensive income resulting from the Tax Cuts and Jobs Act (the "stranded tax effects"). ASU 2018-02 is effective for all entities for fiscal years beginning after December 15, 2018. Early adoption is permitted. The Company elected to early adopt ASU 2018-02 and reclassified $6.6 million of stranded tax effects from accumulated other comprehensive income to retained earnings.

Reclassifications (Policies)

Reclassifications (Policies)	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Reclassifications [Text Block]	Certain prior year amounts have been reclassified to conform to current year presentation. Check card revenue of $19.3 million in 2016 and $19.0 million in 2015 were reclassified from transaction card revenue to deposit service charges and fees

Securities (Tables)

Securities (Tables)	12 Months Ended
	Dec. 31, 2017
Marketable Securities [Abstract]
Trading Securities [Table Text Block]	The fair value and net unrealized gain (loss) included in trading securities is as follows (in thousands): December 31, 2017 December 31, 2016 Fair Value Net Unrealized Gain (Loss) Fair Value Net Unrealized Gain (Loss) U.S. government agency debentures $ 21,196 $ 8 $ 6,234 $ (4 ) U.S. government agency residential mortgage-backed securities 392,673 (517 ) 310,067 635 Municipal and other tax-exempt securities 13,559 83 14,427 50 Asset-backed securities 23,885 (26 ) — — Other trading securities 11,363 4 6,900 57 Total trading securities $ 462,676 $ (448 ) $ 337,628 $ 738
Investment Securities (Held-to-Maturity) [Table Text Block]	The amortized cost and fair values of investment securities are as follows (in thousands): December 31, 2017 Amortized Fair Gross Unrealized Cost Value Gain Loss Municipal and other tax-exempt securities $ 228,186 $ 230,349 $ 2,967 $ (804 ) U.S. government agency residential mortgage-backed securities – Other 15,891 16,242 446 (95 ) Other debt securities 217,716 233,444 17,095 (1,367 ) Total investment securities $ 461,793 $ 480,035 $ 20,508 $ (2,266 ) December 31, 2016 Amortized Fair Gross Unrealized Cost Value Gain Loss Municipal and other tax-exempt securities $ 320,364 $ 321,225 $ 2,272 $ (1,411 ) U.S. government agency residential mortgage-backed securities – Other 20,777 21,473 767 (71 ) Other debt securities 205,004 222,795 18,115 (324 ) Total investment securities $ 546,145 $ 565,493 $ 21,154 $ (1,806 ) The amortized cost and fair values of investment securities at December 31, 2017 , by contractual maturity, are as shown in the following table (dollars in thousands): Less than One Year One to Five Years Six to Ten Years Over Ten Years Total Weighted Average Maturity² Municipal and other tax-exempt securities: Carrying value $ 102,569 $ 74,738 $ 14,929 $ 35,950 $ 228,186 3.51 Fair value 102,414 74,467 15,538 37,930 230,349 Nominal yield¹ 1.82 % 2.34 % 5.06 % 5.19 % 2.73 % Other debt securities: Carrying value $ 13,996 $ 51,502 $ 135,233 $ 16,985 $ 217,716 6.23 Fair value 14,058 53,827 149,517 16,042 233,444 Nominal yield 4.24 % 4.75 % 5.69 % 4.36 % 5.27 % Total fixed maturity securities: Carrying value $ 116,565 $ 126,240 $ 150,162 $ 52,935 $ 445,902 4.83 Fair value 116,472 128,294 165,055 53,972 463,793 Nominal yield 2.11 % 3.32 % 5.63 % 4.92 % 3.97 % Residential mortgage-backed securities: Carrying value $ 15,891 ³ Fair value 16,242 Nominal yield 4 2.76 % Total investment securities: Carrying value $ 461,793 Fair value 480,035 Nominal yield 3.93 % 1 Calculated on a taxable equivalent basis using a 39% effective tax rate. 2 Expected maturities may differ from contractual maturities because borrowers may have the right to call or prepay obligations with or without penalty. 3 The average expected lives of residential mortgage-backed securities were 4.8 years based upon current prepayment assumptions. 4 The nominal yield on residential mortgage-backed securities is based upon prepayment assumptions at the purchase date. Actual yields earned may differ significantly based upon actual prepayments. See Quarterly Financial Summary - Unaudited for current yields on the investment securities portfolio.
Available For Sale Securities [Table Text Block]	The amortized cost and fair value of available for sale securities are as follows (in thousands): December 31, 2017 Amortized Fair Gross Unrealized Cost Value Gain Loss OTTI U.S. Treasury securities $ 1,000 $ 1,000 $ — $ — $ — Municipal and other tax-exempt securities 27,182 27,080 181 (283 ) — Residential mortgage-backed securities: U.S. government agencies: FNMA 3,021,551 2,997,563 11,549 (35,537 ) — FHLMC 1,545,971 1,531,009 3,148 (18,110 ) — GNMA 787,626 780,580 1,607 (8,653 ) — Total U.S. government agencies 5,355,148 5,309,152 16,304 (62,300 ) — Private issue 74,311 93,221 19,301 — (391 ) Total residential mortgage-backed securities 5,429,459 5,402,373 35,605 (62,300 ) (391 ) Commercial mortgage-backed securities guaranteed by U.S. government agencies 2,858,885 2,834,961 1,963 (25,887 ) — Other debt securities 25,500 25,481 50 (69 ) — Perpetual preferred stock 12,562 15,767 3,205 — — Equity securities and mutual funds 14,487 14,916 515 (86 ) — Total available for sale securities $ 8,369,075 $ 8,321,578 $ 41,519 $ (88,625 ) $ (391 ) December 31, 2016 Amortized Fair Gross Unrealized Cost Value Gain Loss OTTI U.S. Treasury securities $ 1,000 $ 999 $ — $ (1 ) $ — Municipal and other tax-exempt securities 41,050 40,993 343 (400 ) — Residential mortgage-backed securities: U.S. government agencies: FNMA 3,062,525 3,055,676 25,066 (31,915 ) — FHLMC 1,534,451 1,531,116 8,475 (11,810 ) — GNMA 878,375 873,594 2,259 (7,040 ) — Total U.S. government agencies 5,475,351 5,460,386 35,800 (50,765 ) — Private issue 101,192 115,535 14,577 (16 ) (218 ) Total residential mortgage-backed securities 5,576,543 5,575,921 50,377 (50,781 ) (218 ) Commercial mortgage-backed securities guaranteed by U.S. government agencies 3,035,750 3,017,933 5,472 (23,289 ) — Other debt securities 4,400 4,152 — (248 ) — Perpetual preferred stock 15,561 18,474 2,913 — — Equity securities and mutual funds 17,424 18,357 1,060 (127 ) — Total available for sale securities $ 8,691,728 $ 8,676,829 $ 60,165 $ (74,846 ) $ (218 ) The amortized cost and fair values of available for sale securities at December 31, 2017 , by contractual maturity, are as shown in the following table (dollars in thousands): Less than One Year One to Five Years Six to Ten Years Over Ten Years Total Weighted Average Maturity 5 U.S. Treasury securities: Amortized cost $ 1,000 $ — $ — $ — $ 1,000 0.04 Fair value 1,000 — — — 1,000 Nominal yield 0.87 % — % — % — % 0.87 % Municipal and other tax-exempt securities: Amortized cost 9,008 2,680 — 15,494 27,182 9.15 Fair value 9,022 2,811 — 15,247 27,080 Nominal yield¹ 3.45 % 6.04 % — % 2.26 % 6 3.03 % Commercial mortgage-backed securities: Amortized cost 22,742 970,611 1,604,465 261,067 2,858,885 7.17 Fair value 22,667 965,099 1,590,107 257,088 2,834,961 Nominal yield 1.49 % 1.93 % 2.03 % 2.03 % 1.99 % Other debt securities: Amortized cost — — — 25,500 25,500 14.68 Fair value — — — 25,481 25,481 Nominal yield — % — % — % 1.59 % 1.59 % Total fixed maturity securities: Amortized cost $ 32,750 $ 973,291 $ 1,604,465 $ 302,061 $ 2,912,567 7.25 Fair value 32,689 967,910 1,590,107 297,816 2,888,522 Nominal yield 2.01 % 1.94 % 2.03 % 2.01 % 2.00 % Residential mortgage-backed securities: Amortized cost $ 5,429,459 2 Fair value 5,402,373 Nominal yield 4 2.04 % Perpetual preferred stock. equity securities and mutual funds: Amortized cost $ 27,049 ³ Fair value 30,683 Nominal yield — % Total available-for-sale securities: Amortized cost $ 8,369,075 Fair value 8,321,578 Nominal yield 2.02 % 1 Calculated on a taxable equivalent basis using a 39% effective tax rate. 2 The average expected lives of mortgage-backed securities were 4.2 years based upon current prepayment assumptions. 3 Primarily common stock and preferred stock of corporate issuers with no stated maturity. 4 The nominal yield on mortgage-backed securities is based upon prepayment assumptions at the purchase date. Actual yields earned may differ significantly based upon actual prepayments. See Quarterly Financial Summary –– Unaudited following for current yields on available for sale securities portfolio. 5 Expected maturities may differ from contractual maturities, because borrowers may have the right to call or prepay obligations with or without penalty. 6 Nominal yield on municipal and other tax-exempt securities and other debt securities with contractual maturity dates over ten years are based on variable rates which generally are reset within 35 days . Sales of available for sale securities resulted in gains and losses as follows (in thousands): Year Ended December 31, 2017 2016 2015 Proceeds $ 1,309,215 $ 899,381 $ 1,600,380 Gross realized gains 10,223 11,696 15,849 Gross realized losses (5,795 ) (21 ) (3,791 ) Related federal and state income tax expense 1,722 4,542 4,691
Securities Pledged As Collateral [Table Text Block]	A summary of investment and available for sale securities that have been pledged as collateral for repurchase agreements, public trust funds on deposit and for other purposes, as required by law was as follows (in thousands): December 31, 2017 2016 Investment: Carrying value $ 226,852 $ 322,208 Fair value 229,429 323,808 Available for sale: Amortized cost 7,151,468 7,353,116 Fair value 7,089,346 7,327,470
Schedule of Unrealized Loss on Investments [Table Text Block]	Temporarily Impaired Securities as of December 31, 2017 (In thousands) Number of Securities Less Than 12 Months 12 Months or Longer Total Fair Value Unrealized Loss Fair Value Unrealized Loss Fair Value Unrealized Loss Investment: Municipal and other tax-exempt securities 100 $ 145,960 $ 643 $ 5,833 $ 161 $ 151,793 $ 804 U.S. government agency residential mortgage-backed securities – Other 1 — — 3,356 95 3,356 95 Other debt securities 49 20,091 1,238 3,076 129 23,167 1,367 Total investment securities 150 $ 166,051 $ 1,881 $ 12,265 $ 385 $ 178,316 $ 2,266 Number of Securities Less Than 12 Months 12 Months or Longer Total Fair Value Unrealized Loss Fair Value Unrealized Loss Fair Value Unrealized Loss Available for sale: U.S. Treasury securities — $ — $ — $ — $ — $ — $ — Municipal and other tax-exempt securities 19 12,765 18 4,802 265 17,567 283 Residential mortgage-backed securities: U.S. government agencies: FNMA 113 1,203,041 9,618 824,029 25,919 2,027,070 35,537 FHLMC 69 863,778 7,297 385,816 10,813 1,249,594 18,110 GNMA 27 201,887 1,452 248,742 7,201 450,629 8,653 Total U.S. agencies 209 2,268,706 18,367 1,458,587 43,933 3,727,293 62,300 Private issue 1 8 5,898 391 — — 5,898 391 Total residential mortgage-backed securities 217 2,274,604 18,758 1,458,587 43,933 3,733,191 62,691 Commercial mortgage-backed securities guaranteed by U.S. government agencies 185 1,465,703 11,824 652,296 14,063 2,117,999 25,887 Other debt securities 2 19,959 41 472 28 20,431 69 Perpetual preferred stock — — — — — — — Equity securities and mutual funds 111 911 7 2,203 79 3,114 86 Total available for sale securities 534 $ 3,773,942 $ 30,648 $ 2,118,360 $ 58,368 $ 5,892,302 $ 89,016 1 Includes securities for which an unrealized loss remains in AOCI after an other-than-temporary credit loss has been recognized in income. Temporarily Impaired Securities as of December 31, 2016 (In thousands) Number of Securities Less Than 12 Months 12 Months or Longer Total Fair Value Unrealized Loss Fair Value Unrealized Loss Fair Value Unrealized Loss Investment: Municipal and other tax- exempt securities 151 $ 219,892 $ 1,316 $ 4,333 $ 95 $ 224,225 $ 1,411 U.S. government agency residential mortgage-backed securities – Other 1 4,358 71 — — 4,358 71 Other debt securities 41 11,820 322 855 2 12,675 324 Total investment securities 193 $ 236,070 $ 1,709 $ 5,188 $ 97 $ 241,258 $ 1,806 Number of Securities Less Than 12 Months 12 Months or Longer Total Fair Value Unrealized Loss Fair Value Unrealized Loss Fair Value Unrealized Loss Available for sale: U.S. Treasury securities 1 $ 999 $ 1 $ — $ — $ 999 $ 1 Municipal and other tax-exempt securities 24 15,666 22 4,689 378 20,355 400 Residential mortgage-backed securities: U. S. government agencies: FNMA 91 1,787,644 30,238 72,105 1,677 1,859,749 31,915 FHLMC 58 964,017 11,210 18,307 600 982,324 11,810 GNMA 31 548,637 6,145 25,796 895 574,433 7,040 Total U.S. agencies 180 3,300,298 47,593 116,208 3,172 3,416,506 50,765 Private issue 1 6 7,931 174 13,508 60 21,439 234 Total residential mortgage-backed securities 186 3,308,229 47,767 129,716 3,232 3,437,945 50,999 Commercial mortgage-backed securities guaranteed by U.S. government agencies 171 1,904,584 22,987 38,875 302 1,943,459 23,289 Other debt securities 2 — — 4,152 248 4,152 248 Perpetual preferred stock — — — — — — — Equity securities and mutual funds 104 2,127 41 817 86 2,944 127 Total available for sale securities 488 $ 5,231,605 $ 70,818 $ 178,249 $ 4,246 $ 5,409,854 $ 75,064 1 Includes securities for which an unrealized loss remains in AOCI after an other-than-temporary credit loss has been recognized in income.
Schedule of Fair Value Option Securities [Table Text Block]	The fair value and net unrealized gain (loss) included in Fair value option securities is as follows (in thousands): December 31, 2017 December 31, 2016 Fair Value Net Unrealized Gain (Loss) Fair Value Net Unrealized Gain (Loss) U.S. government agency residential mortgage-backed securities $ 755,054 $ (1,877 ) $ 77,046 $ (1,777 )
Schedule of Restricted Equity Securities [Table Text Block]	December 31, 2017 2016 Federal Reserve Bank stock $ 40,746 $ 36,498 Federal Home Loan Bank stock 279,200 270,541 Other 243 201 Total $ 320,189 $ 307,240

Derivatives (Tables)

Derivatives (Tables)	12 Months Ended
	Dec. 31, 2017
Derivative Instrument Detail [Abstract]
Derivative Contracts [Table Text Block]	The following table summarizes the fair values of derivative contracts recorded as “derivative contracts” assets and liabilities in the balance sheet at December 31, 2017 (in thousands): Assets Notional 1 Gross Fair Value Netting Adjustments Net Fair Value Before Cash Collateral Cash Collateral Fair Value Net of Cash Collateral Customer risk management programs: Interest rate contracts To-be-announced residential mortgage-backed securities $ 12,347,542 $ 23,606 $ (18,096 ) $ 5,510 $ — $ 5,510 Interest rate swaps 1,478,944 28,278 — 28,278 (4,964 ) 23,314 Energy contracts 1,190,067 103,044 (47,873 ) 55,171 (196 ) 54,975 Agricultural contracts 53,238 1,576 (960 ) 616 — 616 Foreign exchange contracts 132,397 129,551 — 129,551 (448 ) 129,103 Equity option contracts 99,633 5,503 — 5,503 (920 ) 4,583 Total customer risk management programs 15,301,821 291,558 (66,929 ) 224,629 (6,528 ) 218,101 Internal risk management programs 4,736,701 9,494 (7,093 ) 2,401 — 2,401 Total derivative contracts $ 20,038,522 $ 301,052 $ (74,022 ) $ 227,030 $ (6,528 ) $ 220,502 Liabilities Notional¹ Gross Fair Value Netting Adjustments Net Fair Value Before Cash Collateral Cash Collateral Fair Value Net of Cash Collateral Customer risk management programs: Interest rate contracts To-be-announced residential mortgage-backed securities $ 11,537,742 $ 20,367 $ (18,096 ) $ 2,271 $ (704 ) $ 1,567 Interest rate swaps 1,478,944 28,298 — 28,298 (12,896 ) 15,402 Energy contracts 1,166,924 101,603 (47,873 ) 53,730 (42,767 ) 10,963 Agricultural contracts 48,552 1,551 (960 ) 591 — 591 Foreign exchange contracts 126,251 123,321 — 123,321 (53 ) 123,268 Equity option contracts 99,633 5,503 — 5,503 — 5,503 Total customer risk management programs 14,458,046 280,643 (66,929 ) 213,714 (56,420 ) 157,294 Internal risk management programs 5,728,421 21,762 (7,093 ) 14,669 — 14,669 Total derivative contracts $ 20,186,467 $ 302,405 $ (74,022 ) $ 228,383 $ (56,420 ) $ 171,963 1 Notional amounts for commodity contracts are converted into dollar-equivalent amounts based on dollar prices at the inception of the contract. The following table summarizes the fair values of derivative contracts recorded as “derivative contracts” assets and liabilities in the balance sheet at December 31, 2016 (in thousands): Assets Notional 1 Gross Fair Value Netting Adjustments Net Fair Value Before Cash Collateral Cash Collateral Fair Value Net of Cash Collateral Customer risk management programs: Interest rate contracts To-be-announced residential mortgage-backed securities $ 16,949,152 $ 180,695 $ (60,555 ) $ 120,140 $ — $ 120,140 Interest rate swaps 1,403,408 34,442 — 34,442 (4,567 ) 29,875 Energy contracts 835,566 64,140 (28,298 ) 35,842 (71 ) 35,771 Agricultural contracts 53,209 1,382 (515 ) 867 — 867 Foreign exchange contracts 580,886 494,349 — 494,349 (5,183 ) 489,166 Equity option contracts 100,924 4,357 — 4,357 (730 ) 3,627 Total customer risk management programs 19,923,145 779,365 (89,368 ) 689,997 (10,551 ) 679,446 Internal risk management programs 2,514,169 10,426 — 10,426 — 10,426 Total derivative contracts $ 22,437,314 $ 789,791 $ (89,368 ) $ 700,423 $ (10,551 ) $ 689,872 Liabilities Notional¹ Gross Fair Value Netting Adjustments Net Fair Value Before Cash Collateral Cash Collateral Fair Value Net of Cash Collateral Customer risk management programs: Interest rate contracts To-be-announced residential mortgage-backed securities $ 16,637,532 $ 176,928 $ (60,555 ) $ 116,373 $ — $ 116,373 Interest rate swaps 1,403,408 34,442 — 34,442 (11,977 ) 22,465 Energy contracts 820,365 64,306 (28,298 ) 36,008 (31,534 ) 4,474 Agricultural contracts 53,216 1,365 (515 ) 850 (769 ) 81 Foreign exchange contracts 580,712 494,695 — 494,695 (3,630 ) 491,065 Equity option contracts 100,924 4,357 — 4,357 — 4,357 Total customer risk management programs 19,596,157 776,093 (89,368 ) 686,725 (47,910 ) 638,815 Internal risk management programs 2,582,202 25,716 — 25,716 — 25,716 Total derivative contracts $ 22,178,359 $ 801,809 $ (89,368 ) $ 712,441 $ (47,910 ) $ 664,531 1 Notional amounts for commodity contracts are converted into dollar-equivalent amounts based on dollar prices at the inception of the contract.
Derivative Instruments, Gain (Loss) in Statement of Earnings [Table Text Block]	The following summarizes the pre-tax net gains (losses) on derivative instruments and where they are recorded in the Consolidated Statements of Earnings (in thousands): Year Ended December 31, 2017 2016 2015 Brokerage and Trading Revenue Gain (Loss) on Derivatives, Net Brokerage and Trading Revenue Gain (Loss) on Derivatives, Net Brokerage and Trading Revenue Gain (Loss) on Derivatives, Net Customer risk management programs: Interest rate contracts To-be-announced residential mortgage-backed securities $ 34,532 $ — $ 38,523 $ — $ 33,877 $ — Interest rate swaps 2,647 — 2,589 — 2,066 — Energy contracts 5,536 — 5,027 — 4,060 — Agricultural contracts 79 — 111 — 123 — Foreign exchange contracts 1,352 — 945 — 797 — Equity option contracts — — — — — — Total customer risk management programs 44,146 — 47,195 — 40,923 — Internal risk management programs 4,615 779 (4,592 ) (15,685 ) (209 ) 430 Total derivative contracts $ 48,761 $ 779 $ 42,603 $ (15,685 ) $ 40,714 $ 430

Loans and Allowances for Cred32

Loans and Allowances for Credit Losses (Tables)	12 Months Ended
	Dec. 31, 2017
Loans Receivable, Net [Abstract]
Schedule of the Loans by Portfolio Segment [Table Text Block]	The portfolio segments of the loan portfolio are as follows (in thousands): December 31, 2017 December 31, 2016 Fixed Rate Variable Rate Non-accrual Total Fixed Rate Variable Rate Non-accrual Total Commercial $ 2,217,432 $ 8,379,240 $ 137,303 $ 10,733,975 $ 2,327,085 $ 7,884,786 $ 178,953 $ 10,390,824 Commercial real estate 548,692 2,928,440 2,855 3,479,987 624,187 3,179,338 5,521 3,809,046 Residential mortgage 1,608,655 317,584 47,447 1,973,686 1,647,357 256,255 46,220 1,949,832 Personal 154,517 810,990 269 965,776 154,971 684,697 290 839,958 Total $ 4,529,296 $ 12,436,254 $ 187,874 $ 17,153,424 $ 4,753,600 $ 12,005,076 $ 230,984 $ 16,989,660 Accruing loans past due (90 days) 1 $ 633 $ 5 Foregone interest on nonaccrual loans $ 16,496 $ 15,990 1 Excludes residential mortgage loans guaranteed by agencies of the U.S. government
Rollforward of Allowance For Loan Losses And Accrual for Off-Balnace Sheet Credit Losses [Table Text Block]	The activity in the allowance for loan losses and the accrual for off-balance sheet credit risk related to loan commitments and standby letters of credit for the year ended December 31, 2017 is summarized as follows (in thousands): Commercial Commercial Real Estate Residential Mortgage Personal Nonspecific Allowance Total Allowance for loan losses: Beginning balance $ 140,213 $ 50,749 $ 18,224 $ 8,773 $ 28,200 $ 246,159 Provision for loan losses (595 ) 4,008 116 2,964 (5,983 ) 510 Loans charged off (19,810 ) (76 ) (649 ) (5,064 ) — (25,599 ) Recoveries 4,461 1,940 760 2,451 — 9,612 Ending balance $ 124,269 $ 56,621 $ 18,451 $ 9,124 $ 22,217 $ 230,682 Accrual for off-balance sheet credit risk: Beginning balance $ 11,063 $ 123 $ 50 $ 8 $ — $ 11,244 Provision for off-balance sheet credit risk (7,419 ) (78 ) (7 ) (6 ) — (7,510 ) Ending balance $ 3,644 $ 45 $ 43 $ 2 $ — $ 3,734 Total provision for credit losses $ (8,014 ) $ 3,930 $ 109 $ 2,958 $ (5,983 ) $ (7,000 ) The activity in the allowance for loan losses and the accrual for off-balance sheet credit risk related to loan commitments and standby letters of credit for the year ended December 31, 2016 is summarized as follows (in thousands): Commercial Commercial Real Estate Residential Mortgage Personal Nonspecific Allowance Total Allowance for loan losses: Beginning balance $ 130,334 $ 41,391 $ 19,509 $ 4,164 $ 30,126 $ 225,524 Provision for loan losses 43,980 8,075 (1,972 ) 7,310 (1,926 ) 55,467 Loans charged off (35,828 ) — (1,312 ) (5,448 ) — (42,588 ) Recoveries 1,727 1,283 1,999 2,747 — 7,756 Ending balance $ 140,213 $ 50,749 $ 18,224 $ 8,773 $ 28,200 $ 246,159 Accrual for off-balance sheet credit risk: Beginning balance $ 1,506 $ 153 $ 30 $ 22 $ — $ 1,711 Provision for off-balance sheet credit risk 9,557 (30 ) 20 (14 ) — 9,533 Ending balance $ 11,063 $ 123 $ 50 $ 8 $ — $ 11,244 Total provision for credit losses $ 53,537 $ 8,045 $ (1,952 ) $ 7,296 $ (1,926 ) $ 65,000 The activity in the allowance for loan losses and the accrual for off-balance sheet credit risk related to loan commitments and standby letters of credit for the year ended December 31, 2015 is summarized as follows (in thousands): Commercial Commercial Real Estate Residential Mortgage Personal Nonspecific Allowance Total Allowance for loan losses: Beginning balance $ 90,875 $ 42,445 $ 23,458 $ 4,233 $ 28,045 $ 189,056 Provision for loan losses 43,464 (11,189 ) (3,004 ) 2,167 2,081 33,519 Loans charged off (6,734 ) (944 ) (2,205 ) (5,288 ) — (15,171 ) Recoveries 2,729 11,079 1,260 3,052 — 18,120 Ending balance $ 130,334 $ 41,391 $ 19,509 $ 4,164 $ 30,126 $ 225,524 Accrual for off-balance sheet credit risk: Beginning balance $ 475 $ 707 $ 28 $ 20 $ — $ 1,230 Provision for off-balance sheet credit risk 1,031 (554 ) 2 2 — 481 Ending balance $ 1,506 $ 153 $ 30 $ 22 $ — $ 1,711 Total provision for credit losses $ 44,495 $ (11,743 ) $ (3,002 ) $ 2,169 $ 2,081 $ 34,000 The allowance for loan losses and recorded investment of the related loans by portfolio segment for each impairment measurement method at December 31, 2017 is as follows (in thousands): Collectively Measured for Impairment Individually Measured for Impairment Total Recorded Investment Related Allowance Recorded Investment Related Allowance Recorded Investment Related Allowance Commercial $ 10,596,672 $ 115,438 $ 137,303 $ 8,831 $ 10,733,975 $ 124,269 Commercial real estate 3,477,132 56,621 2,855 — 3,479,987 56,621 Residential mortgage 1,926,239 18,451 47,447 — 1,973,686 18,451 Personal 965,507 9,124 269 — 965,776 9,124 Total 16,965,550 199,634 187,874 8,831 17,153,424 208,465 Nonspecific allowance — — — — — 22,217 Total $ 16,965,550 $ 199,634 $ 187,874 $ 8,831 $ 17,153,424 $ 230,682 The allowance for loan losses and recorded investment of the related loans by portfolio segment for each impairment measurement method at December 31, 2016 is as follows (in thousands): Collectively Measured for Impairment Individually Measured for Impairment Total Recorded Investment Related Allowance Recorded Investment Related Allowance Recorded Investment Related Allowance Commercial $ 10,211,871 $ 139,416 $ 178,953 $ 797 $ 10,390,824 $ 140,213 Commercial real estate 3,803,525 50,749 5,521 — 3,809,046 50,749 Residential mortgage 1,903,612 18,178 46,220 46 1,949,832 18,224 Personal 839,668 8,773 290 — 839,958 8,773 Total 16,758,676 217,116 230,984 843 16,989,660 217,959 Nonspecific allowance — — — — — 28,200 Total $ 16,758,676 $ 217,116 $ 230,984 $ 843 $ 16,989,660 $ 246,159
Schedule of Allowance for Loan Losses and Recorded Investment by Portfolio Segment for Risk Graded and Non-Risk Graded Loans [Table Text Block]	The allowance for loan losses and recorded investment of the related loans by portfolio segment for risk graded and non-risk graded loans at December 31, 2017 is as follows (in thousands): Internally Risk Graded Non-Graded Total Recorded Investment Related Allowance Recorded Investment Related Allowance Recorded Investment Related Allowance Commercial $ 10,706,035 $ 123,383 $ 27,940 $ 886 $ 10,733,975 $ 124,269 Commercial real estate 3,479,987 56,621 — — 3,479,987 56,621 Residential mortgage 234,477 2,947 1,739,209 15,504 1,973,686 18,451 Personal 877,390 6,461 88,386 2,663 965,776 9,124 Total 15,297,889 189,412 1,855,535 19,053 17,153,424 208,465 Nonspecific allowance — — — — — 22,217 Total $ 15,297,889 $ 189,412 $ 1,855,535 $ 19,053 $ 17,153,424 $ 230,682 The allowance for loan losses and recorded investment of the related loans by portfolio segment for risk graded and non-risk graded loans at December 31, 2016 is as follows (in thousands): Internally Risk Graded Non-Graded Total Recorded Investment Related Allowance Recorded Investment Related Allowance Recorded Investment Related Allowance Commercial $ 10,360,725 $ 139,293 $ 30,099 $ 920 $ 10,390,824 $ 140,213 Commercial real estate 3,809,046 50,749 — — 3,809,046 50,749 Residential mortgage 243,703 2,893 1,706,129 15,331 1,949,832 18,224 Personal 744,602 5,035 95,356 3,738 839,958 8,773 Total 15,158,076 197,970 1,831,584 19,989 16,989,660 217,959 Nonspecific allowance — — — — — 28,200 Total $ 15,158,076 $ 197,970 $ 1,831,584 $ 19,989 $ 16,989,660 $ 246,159
Schedule of Credit Quality Indicators [Table Text Block]	The following table summarizes the Company’s loan portfolio at December 31, 2017 by the risk grade categories (in thousands): Internally Risk Graded Non-Graded Performing Pass Other Loans Especially Mentioned Accruing Substandard Nonaccrual Performing Nonaccrual Total Commercial: Energy $ 2,632,986 $ 60,288 $ 144,598 $ 92,284 $ — $ — $ 2,930,156 Services 2,943,869 13,927 26,533 2,620 — — 2,986,949 Wholesale/retail 1,443,917 19,263 5,502 2,574 — — 1,471,256 Manufacturing 472,869 6,653 11,290 5,962 — — 496,774 Healthcare 2,253,497 3,186 43,305 14,765 — — 2,314,753 Other commercial and industrial 478,951 7 8,161 19,028 27,870 70 534,087 Total commercial 10,226,089 103,324 239,389 137,233 27,870 70 10,733,975 Commercial real estate: Residential construction and land development 113,190 1,828 395 1,832 — — 117,245 Retail 686,915 4,243 98 276 — — 691,532 Office 824,408 7,087 — 275 — — 831,770 Multifamily 979,969 — 48 — — — 980,017 Industrial 573,014 — — — — — 573,014 Other commercial real estate 285,506 145 286 472 — — 286,409 Total commercial real estate 3,463,002 13,303 827 2,855 — — 3,479,987 Residential mortgage: Permanent mortgage 232,492 — 822 1,163 784,928 24,030 1,043,435 Permanent mortgages guaranteed by U.S. government agencies — — — — 188,327 9,179 197,506 Home equity — — — — 719,670 13,075 732,745 Total residential mortgage 232,492 — 822 1,163 1,692,925 46,284 1,973,686 Personal 875,696 1,548 63 83 88,200 186 965,776 Total $ 14,797,279 $ 118,175 $ 241,101 $ 141,334 $ 1,808,995 $ 46,540 $ 17,153,424 The following table summarizes the Company’s loan portfolio at December 31, 2016 by the risk grade categories (in thousands): Internally Risk Graded Non-Graded Performing Pass Other Loans Especially Mentioned Accruing Substandard Nonaccrual Performing Nonaccrual Total Commercial: Energy $ 1,937,790 $ 119,583 $ 307,996 132,499 $ — $ — $ 2,497,868 Services 3,052,002 10,960 37,855 8,173 — — 3,108,990 Wholesale/retail 1,535,463 16,886 13,062 11,407 — — 1,576,818 Manufacturing 468,314 26,532 15,198 4,931 — — 514,975 Healthcare 2,140,458 44,472 16,161 825 — — 2,201,916 Other commercial and industrial 433,789 5,309 — 21,060 30,041 58 490,257 Total commercial 9,567,816 223,742 390,272 178,895 30,041 58 10,390,824 Commercial real estate: Residential construction and land development 131,630 — 470 3,433 — — 135,533 Retail 756,418 4,745 399 326 — — 761,888 Office 798,462 — — 426 — — 798,888 Multifamily 898,800 — 4,434 38 — — 903,272 Industrial 871,673 — — 76 — — 871,749 Other commercial real estate 336,488 — 6 1,222 — — 337,716 Total commercial real estate 3,793,471 4,745 5,309 5,521 — — 3,809,046 Residential mortgage: Permanent mortgage 238,769 1,186 2,331 1,417 741,679 21,438 1,006,820 Permanent mortgages guaranteed by U.S. government agencies — — — — 187,541 11,846 199,387 Home equity — — — — 732,106 11,519 743,625 Total residential mortgage 238,769 1,186 2,331 1,417 1,661,326 44,803 1,949,832 Personal 743,451 — 1,054 97 95,163 193 839,958 Total $ 14,343,507 $ 229,673 $ 398,966 185,930 $ 1,786,530 $ 45,054 $ 16,989,660
Summary of Impaired Loans [Table Text Block]	As of December 31, 2017 Year Ended Recorded Investment December 31, 2017 Unpaid Principal Balance Total With No With Allowance Related Allowance Average Recorded Interest Income Recognized Commercial: Energy $ 111,011 $ 92,284 $ 40,968 $ 51,316 $ 8,814 $ 112,392 $ — Services 5,324 2,620 2,620 — — 5,396 — Wholesale/retail 9,099 2,574 2,574 — — 6,990 — Manufacturing 6,073 5,962 5,962 — — 5,446 — Healthcare 25,140 14,765 14,765 — — 7,795 — Other commercial and industrial 27,957 19,098 19,080 18 17 20,108 — Total commercial 184,604 137,303 85,969 51,334 8,831 158,127 — Commercial real estate: Residential construction and land development 3,285 1,832 1,832 — — 2,633 — Retail 509 276 276 — — 301 — Office 287 275 275 — — 351 — Multifamily — — — — — 19 — Industrial — — — — — 38 — Other commercial real estate 670 472 472 — — 847 — Total commercial real estate 4,751 2,855 2,855 — — 4,189 — Residential mortgage: Permanent mortgage 30,435 25,193 25,193 — — 24,024 1,229 Permanent mortgage guaranteed by U.S. government agencies 1 203,814 197,506 197,506 — — 199,244 7,632 Home equity 14,548 13,075 13,075 — — 12,297 — Total residential mortgage 248,797 235,774 235,774 — — 235,565 8,861 Personal 307 269 269 — — 280 — Total $ 438,459 $ 376,201 $ 324,867 $ 51,334 $ 8,831 $ 398,161 $ 8,861 1 All permanent mortgage loans guaranteed by U.S. government agencies are considered impaired as we do not expect full collection of contractual principal and interest. At December 31, 2017 , $9.2 million of these loans are nonaccruing and $188 million are accruing based on the guarantee by U.S. government agencies. Generally, no interest income is recognized on impaired loans until all principal balances, including amounts charged-off, have been recovered. During 2017, we recognized $7.2 million as interest income on impaired loans that meet these conditions. As of December 31, 2016 Year Ended Recorded Investment December 31, 2016 Unpaid Principal Balance Total With No Allowance With Allowance Related Allowance Average Recorded Investment Interest Income Recognized Commercial: Energy $ 146,897 $ 132,499 $ 121,418 $ 11,081 $ 762 $ 80,100 $ — Services 11,723 8,173 8,173 — — 9,232 — Wholesale/retail 17,669 11,407 11,407 — — 7,163 — Manufacturing 5,320 4,931 4,931 — — 2,631 — Healthcare 1,147 825 825 — — 949 — Other commercial and industrial 29,006 21,118 21,083 35 35 10,870 — Total commercial 211,762 178,953 167,837 11,116 797 110,945 — Commercial real estate: Residential construction and land development 4,951 3,433 3,433 — — 3,921 — Retail 530 326 326 — — 823 — Office 521 426 426 — — 539 — Multifamily 1,000 38 38 — — 156 — Industrial 76 76 76 — — 76 — Other commercial real estate 7,349 1,222 1,222 — — 1,747 — Total commercial real estate 14,427 5,521 5,521 — — 7,262 — Residential mortgage: Permanent mortgage 28,830 22,855 22,809 46 46 25,920 1,255 Permanent mortgage guaranteed by U.S. government agencies 1 205,564 199,387 199,387 — — 193,889 7,759 Home equity 12,611 11,519 11,519 — — 10,937 — Total residential mortgage 247,005 233,761 233,715 46 46 230,746 9,014 Personal 332 290 290 — — 377 — Total $ 473,526 $ 418,525 $ 407,363 $ 11,162 $ 843 $ 349,330 $ 9,014 1 All permanent mortgage loans guaranteed by U.S. government agencies are considered impaired as we do not expect full collection of contractual principal and interest. At December 31, 2016 , $12 million of these loans are nonaccruing and $188 million are accruing based on the guarantee by U.S. government agencies.
Summary of Loans by Aging Status [Table Text Block]	A summary of loans currently performing, loans past due and accruing and nonaccrual loans as of December 31, 2017 is as follows (in thousands): Past Due Current 30 to 59 Days 60 to 89 Days 90 Days or More Nonaccrual Total Commercial: Energy $ 2,833,668 $ — 4,204 $ — $ 92,284 $ 2,930,156 Services 2,983,222 514 486 107 2,620 2,986,949 Wholesale/retail 1,468,284 398 — — 2,574 1,471,256 Manufacturing 490,739 — 73 — 5,962 496,774 Healthcare 2,284,770 15,218 — — 14,765 2,314,753 Other commercial and industrial 514,701 85 78 125 19,098 534,087 Total commercial 10,575,384 16,215 4,841 232 137,303 10,733,975 Commercial real estate: Residential construction and land development 115,213 200 — — 1,832 117,245 Retail 691,256 — — — 276 691,532 Office 831,118 254 — 123 275 831,770 Multifamily 979,625 22 370 — — 980,017 Industrial 573,014 — — — — 573,014 Other commercial real estate 285,937 — — — 472 286,409 Total commercial real estate 3,476,163 476 370 123 2,855 3,479,987 Residential mortgage: Permanent mortgage 1,014,588 3,435 219 — 25,193 1,043,435 Permanent mortgages guaranteed by U.S. government agencies 22,692 18,978 13,468 133,189 9,179 197,506 Home equity 717,007 2,206 440 17 13,075 732,745 Total residential mortgage 1,754,287 24,619 14,127 133,206 47,447 1,973,686 Personal 964,374 681 191 261 269 965,776 Total $ 16,770,208 $ 41,991 19,529 $ 133,822 $ 187,874 $ 17,153,424 A summary of loans currently performing, loans past due and accruing and nonaccrual loans as of December 31, 2016 is as follows (in thousands): Past Due Current 30 to 59 Days 60 to 89 Days 90 Days or More Nonaccrual Total Commercial: Energy $ 2,364,890 $ 479 — $ — $ 132,499 $ 2,497,868 Services 3,099,605 191 1,021 — 8,173 3,108,990 Wholesale/retail 1,561,650 3,761 — — 11,407 1,576,818 Manufacturing 509,662 382 — — 4,931 514,975 Healthcare 2,201,050 — 41 — 825 2,201,916 Other commercial and industrial 468,981 155 3 — 21,118 490,257 Total commercial 10,205,838 4,968 1,065 — 178,953 10,390,824 Commercial real estate: Residential construction and land development 132,100 — — — 3,433 135,533 Retail 761,562 — — — 326 761,888 Office 798,462 — — — 426 798,888 Multifamily 903,234 — — — 38 903,272 Industrial 871,673 — — — 76 871,749 Other commercial real estate 336,488 6 — — 1,222 337,716 Total commercial real estate 3,803,519 6 — — 5,521 3,809,046 Residential mortgage: Permanent mortgage 979,386 3,299 1,280 — 22,855 1,006,820 Permanent mortgages guaranteed by U.S. government agencies 40,594 17,465 13,803 115,679 11,846 199,387 Home equity 729,493 2,276 337 — 11,519 743,625 Total residential mortgage 1,749,473 23,040 15,420 115,679 46,220 1,949,832 Personal 838,811 589 263 5 290 839,958 Total $ 16,597,641 $ 28,603 16,748 $ 115,684 $ 230,984 $ 16,989,660

Premises and Equipment Premises

Premises and Equipment Premises and Equipment (Tables)	12 Months Ended
	Dec. 31, 2017
Property, Plant and Equipment [Abstract]
Premises and Equipment [Table Text Block]	Premises and equipment at December 31 are summarized as follows (in thousands): December 31, 2017 2016 Land $ 71,348 $ 70,552 Buildings and improvements 249,139 250,311 Software 188,826 158,155 Furniture and equipment 223,163 217,399 Construction in progress 23,348 36,743 Premises and equipment 755,824 733,160 Less accumulated depreciation 438,489 407,311 Premises and equipment, net of accumulated depreciation $ 317,335 $ 325,849

Goodwill and Intangible Assets

Goodwill and Intangible Assets (Tables)	12 Months Ended
	Dec. 31, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of Finite-Lived Intangible Assets [Table Text Block]	The following table presents the original cost and accumulated amortization of intangible assets (in thousands): Dec. 31, 2017 2016 Core deposit premiums $ 6,510 $ 35,879 Less accumulated amortization 808 29,369 Net core deposit premiums 5,702 6,510 Other identifiable intangible assets 44,468 60,951 Less accumulated amortization 21,512 20,530 Net other identifiable intangible assets 22,956 40,421 Total intangible assets, net $ 28,658 $ 46,931
Schedule of Finite-Lived Intangible Assets, Future Amortization Expense [Table Text Block]	Expected amortization expense for intangible assets that will continue to be amortized (in thousands): Core Deposit Premiums Other Identifiable Intangible Assets Total 2018 $ 732 $ 4,322 $ 5,054 2019 716 3,970 4,686 2020 697 3,834 4,531 2021 675 3,477 4,152 2022 649 2,628 3,277 Thereafter 2,233 4,725 6,958 $ 5,702 $ 22,956 $ 28,658
Schedule of Goodwill [Table Text Block]	The changes in the carrying value of goodwill by operating segment are as follows (in thousands): Commercial Banking Consumer Banking Wealth Management Funds Management and Other Total Balance, December 31, 2015 Goodwill $ 277,044 $ 39,251 $ 69,394 $ — $ 385,689 Accumulated impairment losses — (228 ) — — (228 ) 277,044 39,023 69,394 — 385,461 Goodwill recognized during 2016 1,210 — 2,126 66,160 69,496 Adjustment 2 $ (6,058 ) $ — $ — $ — (6,058 ) Balance, December 31, 2016 Goodwill 272,196 39,251 71,520 66,160 449,127 Accumulated impairment losses — (228 ) — — (228 ) 272,196 39,023 71,520 66,160 448,899 Goodwill recognized during 2017 4,301 — — — 4,301 Sales of consolidated merchant banking investments during 2017 (5,219 ) — (25 ) — (5,244 ) Adjustment 1 41,992 4,435 19,207 (66,160 ) (526 ) Balance, December 31, 2017 Goodwill 313,270 43,686 90,702 — 447,658 Accumulated impairment losses — (228 ) — — (228 ) $ 313,270 $ 43,458 $ 90,702 $ — $ 447,430 1

Mortgage Banking Activities (Ta

Mortgage Banking Activities (Tables)	12 Months Ended
	Dec. 31, 2017
Mortgage Banking [Abstract]
Components of Residential Mortgage Loans Held For Sale [Table Text Block]	The unpaid principal balance of residential mortgage loans held for sale, notional amounts of derivative contracts related to residential mortgage loan commitments and forward contract sales and their related fair values included in Mortgage loans held for sale on the Consolidated Balance Sheets were (in thousands): December 31, 2017 December 31, 2016 Unpaid Principal Balance/ Notional Fair Value Unpaid Principal Balance/ Notional Fair Value Residential mortgage loans held for sale $ 212,525 $ 215,113 $ 286,414 $ 286,971 Residential mortgage loan commitments 222,919 6,523 318,359 9,733 Forward sales contracts 380,159 (258 ) 569,543 5,193 $ 221,378 $ 301,897
Mortgage Banking Revenue [Table Text Block]	Mortgage banking revenue was as follows (in thousands): Year Ended 2017 2016 2015 Production revenue: Net realized gains on sales of mortgage loans $ 45,128 $ 68,947 $ 67,407 Net change in unrealized gain on mortgage loans held for sale 2,031 (5,311 ) (784 ) Net change in the fair value of mortgage loan commitments (3,210 ) 1,599 (1,837 ) Net change in the fair value of forward sales contracts (5,451 ) 4,393 4,801 Total mortgage production revenue 38,498 69,628 69,587 Servicing revenue 66,221 64,286 56,415 Total mortgage banking revenue $ 104,719 $ 133,914 $ 126,002
Summary of Mortgage Servicing Rights [Table Text Block]	The following represents a summary of mortgage servicing rights (Dollars in thousands): December 31, 2017 2016 2015 Number of residential mortgage loans serviced for others 136,528 139,340 131,859 Outstanding principal balance of residential mortgage loans serviced for others $ 22,046,632 $ 21,997,568 $ 19,678,226 Weighted average interest rate 3.94 % 3.97 % 4.12 % Remaining contractual term (in months) 297 301 300
Activity in Capitalized Mortgage Servicing Rights [Table Text Block]	Activity in capitalized mortgage servicing rights during the three years ended December 31, 2017 is as follows (in thousands): Balance, December 31, 2014 $ 171,976 Additions, net 79,546 Change in fair value due to loan runoff (28,064 ) Change in fair value due to market changes (4,853 ) Balance, December 31, 2015 218,605 Additions, net 71,405 Change in fair value due to loan runoff (40,744 ) Change in fair value due to market changes (2,193 ) Balance, December 31, 2016 247,073 Additions, net 39,149 Change in fair value due to loan runoff (33,527 ) Change in fair value due to market changes 172 Balance, December 31, 2017 $ 252,867
Assumptions to Value Mortgage Servicing Rights [Table Text Block]	Significant assumptions used to determine fair value considered to be significant unobservable inputs were as follows: December 31, 2017 2016 Discount rate – risk-free rate plus a market premium 9.84% 10.08% Prepayment rate - based upon loan interest rate, original term and loan type 8.72%-15.16% 8.98%-16.91% Loan servicing costs – annually per loan based upon loan type: Performing loans $65 - $88 $63 - $120 Delinquent loans $150 - $500 $150 - $500 Loans in foreclosure $1,000 - $4,000 $650 - $4,250 Primary/secondary mortgage rate spread 105 bps 105 bps Escrow earnings rate – indexed to rates paid on deposit accounts with comparable average life 2.24% 1.98%
Aging Status of Mortgage Loans Serviced For Others [Table Text Block]	The aging status of our mortgage loans serviced for others by investor at December 31, 2017 follows (in thousands): Past Due Current 30 to 59 Days 60 to 89 Days 90 Days or More Total FHLMC $ 7,995,369 $ 81,805 $ 14,091 $ 32,756 $ 8,124,021 FNMA 6,595,410 81,405 13,856 27,083 6,717,754 GNMA 6,431,808 232,937 60,556 19,743 6,745,044 Other 452,227 4,271 1,128 2,187 459,813 Total $ 21,474,814 $ 400,418 $ 89,631 $ 81,769 $ 22,046,632

Deposits (Tables)

Deposits (Tables)	12 Months Ended
	Dec. 31, 2017
Deposits [Abstract]
Interest Expense on Deposits Disclosure [Table Text Block]	Interest expense on deposits is summarized as follows (in thousands): Year Ended December 31, 2017 2016 2015 Transaction deposits $ 28,627 $ 13,906 $ 8,821 Savings 359 386 383 Time: Certificates of deposits under $100,000 7,702 8,776 11,894 Certificates of deposits $100,000 and over 12,393 10,123 10,643 Other time deposits 4,722 7,303 12,429 Total time 24,817 26,202 34,966 Total $ 53,803 $ 40,494 $ 44,170

Other Borrowings Other Borrowin

Other Borrowings Other Borrowings (Tables)	12 Months Ended
	Dec. 31, 2017
Debt Disclosure [Abstract]
Schedule of Other Borrowings [Table Text Block]	Information relating to other borrowings is summarized as follows (dollars in thousands): As of Year Ended December 31, 2017 December 31, 2017 Balance Rate Average Balance Rate Maximum Parent company and other non-bank subsidiaries: Trust preferred debt $ — — % $ 3,296 3.52 % $ 7,217 Other — — % 935 11.11 % 3,104 Total other borrowings — 4,231 7.00 % Subordinated debentures 144,677 5.60 % 144,658 5.62 % $ 144,677 Total parent company and other non-bank subsidiaries 144,677 148,889 5.65 % BOKF, NA: Funds purchased 58,628 1.00 % 58,064 0.73 % 80,967 Repurchase agreements 516,335 0.17 % 433,791 0.10 % 536,094 Other borrowings: Federal Home Loan Bank advances 5,100,000 1.47 % 5,882,466 1.13 % 6,200,000 GNMA repurchase liability 19,947 4.22 % 20,509 4.59 % 24,139 Other 14,950 2.61 % 15,382 2.38 % 15,506 Total other borrowings 5,134,897 5,918,357 1.14 % Subordinated debentures — — % — — % — Total BOKF, NA 5,709,860 6,410,212 1.07 % Total other borrowed funds $ 5,854,537 $ 6,559,101 1.18 % As of Year Ended December 31, 2016 December 31, 2016 Balance Rate Average Balance Rate Maximum Parent company and other non-bank subsidiaries: Trust preferred debt $ 7,217 3.28 % $ 611 3.27 % $ 7,217 Other 1,092 8.27 % 2,073 16.11 % 3,157 Total other borrowings 8,309 2,684 13.19 % Subordinated debentures 144,640 5.60 % 74,428 5.59 % 145,393 Total parent company and other non-bank subsidiaries 152,949 77,112 5.86 % BOKF, NA: Funds purchased 57,929 0.38 % 78,222 0.24 % 567,103 Repurchase agreements 668,661 0.02 % 589,145 0.04 % 668,661 Other borrowings: Federal Home Loan Bank advances 4,800,000 0.72 % 5,985,656 0.55 % 6,500,000 GNMA repurchase liability 22,471 4.26 % 15,637 4.74 % 22,471 Other 15,292 2.66 % 15,670 2.41 % 15,797 Total other borrowings 4,837,763 6,016,963 0.57 % Subordinated debentures — — % 140,414 1.35 % 226,434 Total BOKF, NA 5,564,353 6,824,744 0.54 % Total other borrowed funds $ 5,717,302 $ 6,901,856 0.60 % As of Year Ended December 31, 2015 December 31, 2015 Balance Rate Average Balance Rate Maximum Parent company and other non-bank subsidiaries: Trust preferred debt $ — — % $ — — % $ — Other — — % — — % — Total other borrowings — — — % Subordinated debentures — — % — — % — Total parent company and other non-bank subsidiaries — — — % BOKF, NA: Funds purchased 491,192 0.15 % 73,219 0.09 % 491,192 Repurchase agreements 722,444 0.02 % 623,921 0.04 % 1,008,144 Other borrowings: Federal Home Loan Bank advances 4,800,000 0.48 % 4,921,739 0.28 % 5,000,000 GNMA repurchase liability 19,478 4.75 % 16,668 4.95 % 19,478 Other 18,402 2.70 % 18,768 2.35 % 26,058 Total other borrowings 4,837,880 4,957,175 0.33 % Subordinated debentures 226,350 1.05 % 226,332 1.84 % 348,076 Total BOKF, NA 6,277,866 5,880,647 0.36 % Total other borrowed funds $ 6,277,866 $ 5,880,647 0.36 %
Schedule of Maturities of Other Borrowings [Table Text Block]	Aggregate annual principal repayments at December 31, 2017 are as follows (in thousands): Parent Company and Other Non-bank Subsidiaries BOKF, NA 2018 $ — $ 5,695,621 2019 — 956 2020 — 961 2021 — 965 2022 — 970 Thereafter 144,677 10,387 Total $ 144,677 $ 5,709,860
Schedule of Repurchase Agreements [Table Text Block]	Additional information relating to securities sold under agreements to repurchase and related liabilities at December 31, 2017 and 2016 is as follows (dollars in thousands): December 31, 2017 Amortized Fair Repurchase Average Security Sold/Maturity Cost Value Liability 1 Rate U.S. government agency mortgage-backed securities: Overnight 1 $ 525,452 $ 523,914 $ 516,335 0.17 % Long-term — — — — % Total Agency Securities $ 525,452 $ 523,914 $ 516,335 0.17 % December 31, 2016 Amortized Fair Repurchase Average Security Sold/Maturity Cost Value Liability 1 Rate U.S. government agency mortgage-backed securities: Overnight 1 $ 655,529 $ 655,851 $ 668,661 0.02 % Long-term — — — — % Total Agency Securities $ 655,529 $ 655,851 $ 668,661 0.02 % 1 BOK Financial maintains control over the securities underlying overnight repurchase agreements and generally transfers control over securities underlying longer-term dealer repurchase agreements to the respective counterparty.

Federal and State Income Taxes

Federal and State Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Schedule of Deferred Tax Assets and Liabilities [Table Text Block]	The Tax Cuts and Jobs Act (the "Act"), which was enacted on December 22, 2017, reduces the federal corporate tax rate from 35% to 21% for periods beginning January 1, 2018. Provisions of the Act are broad and complex. As result, we are still evaluating the impact that certain aspects of the Act will have on the Company's financial position and results of operations, including recognition and measurement of deferred tax assets and liabilities and the determination of effective current and deferred federal and state income tax rates. We have made reasonable estimates of the Act's impact on net deferred tax assets and recorded a provisional adjustment of $9.5 million , including $6.4 million of net deferred tax assets resulting from temporary differences recognized in Accumulated other comprehensive income on the Company's balance sheets. Additionally, we recognized a provisional adjustment of $2.2 million for deferred taxes resulting from executive compensation that may no longer be deductible. We are not aware of any material areas where we were not able to determine provisional amounts. However, accounting for income tax effects of the Act is still in process and provisional adjustments recognized in 2017 may be adjusted as a result of our on-going evaluation, including subsequent guidance provided by federal and state taxing authorities and other information as it becomes available. Deferred income taxes reflect the net tax effects of temporary differences between the carrying amounts of assets and liabilities for financial reporting purposes and the amounts used for income tax purposes. As a result of the Act, deferred tax balances at December 31, 2017 generally have been revalued from the previous combined federal and state statutory rate of 38.9% to 25.5% . Significant components of deferred tax assets and liabilities are as follows (in thousands): December 31, 2017 2016 Deferred tax assets: Available for sale securities mark to market $ 12,083 $ 5,779 Share-based compensation 7,598 9,360 Credit loss allowances 58,666 99,191 Valuation adjustments 8,102 12,222 Deferred compensation 12,215 30,262 Unearned fees 9,265 11,877 Other 30,859 42,541 Total deferred tax assets 138,788 211,232 Deferred tax liabilities: Depreciation 15,817 25,877 Mortgage servicing rights 63,112 92,748 Lease financing 9,973 17,923 Other 34,880 45,363 Total deferred tax liabilities 123,782 181,911 Net deferred tax assets $ 15,006 $ 29,321
Schedule of Components of Income Tax Expense (Benefit) [Table Text Block]	The significant components of the provision for income taxes attributable to continuing operations for BOK Financial are shown below (in thousands): Year Ended December 31, 2017 2016 2015 Current income tax expense: Federal $ 141,607 $ 107,379 $ 117,566 State 14,592 11,028 12,397 Total current income tax expense 156,199 118,407 129,963 Deferred income tax expense: Federal 25,525 (11,340 ) 8,397 State 869 (690 ) 1,024 Total deferred income tax expense 26,394 (12,030 ) 9,421 Total income tax expense $ 182,593 $ 106,377 $ 139,384
Schedule of Effective Income Tax Rate Reconciliation [Table Text Block]	The reconciliations of income attributable to continuing operations at the U.S. federal statutory tax rate to income tax expense are as follows (in thousands): Year Ended December 31, 2017 2016 2015 Amount: Federal statutory tax $ 181,397 $ 118,530 $ 151,075 Tax exempt revenue (12,402 ) (10,544 ) (9,553 ) Effect of state income taxes, net of federal benefit 10,701 6,478 9,082 Utilization of tax credits: Low-income housing tax credits, net of amortization (5,356 ) (4,171 ) (3,874 ) Other tax credits (1,455 ) (2,085 ) (2,085 ) Bank-owned life insurance (3,121 ) (2,911 ) (3,264 ) Share-based compensation (2,817 ) — — Revaluation of net deferred tax assets due to change in federal tax rates 9,456 — — Write-off of deferred tax assets related to executive compensation 2,216 — — Other, net 3,974 1,080 (1,997 ) Total income tax expense $ 182,593 $ 106,377 $ 139,384 Year Ended December 31, 2017 2016 2015 Percent of pretax income: Federal statutory tax 35.0 % 35.0 % 35.0 % Tax exempt revenue (2.4 ) (3.1 ) (2.2 ) Effect of state income taxes, net of federal benefit 2.0 1.9 2.1 Utilization of tax credits: Low-income housing tax credits, net of amortization (1.0 ) (1.2 ) (0.9 ) Other tax credits (0.3 ) (0.6 ) (0.5 ) Bank-owned life insurance (0.6 ) (0.9 ) (0.7 ) Share-based compensation (0.5 ) — — Revaluation of net deferred tax assets due to change in federal tax rates 1.8 — — Write-off of deferred tax assets related to executive compensation 0.4 — — Other, net 0.8 0.3 (0.5 ) Total 35.2 % 31.4 % 32.3 %
Schedule of Unrecognized Tax Benefits Roll Forward [Table Text Block]	A reconciliation of the beginning and ending amount of unrecognized tax benefits is as follows (in thousands): 2017 2016 2015 Balance as of January 1 $ 15,841 $ 13,232 $ 13,374 Additions for tax for current year positions 4,645 5,640 2,226 Settlements during the period — — — Lapses of applicable statute of limitations (2,376 ) (3,031 ) (2,368 ) Balance as of December 31 $ 18,110 $ 15,841 $ 13,232

Employee Benefits (Tables)

Employee Benefits (Tables)	12 Months Ended
	Dec. 31, 2017
Retirement Benefits [Abstract]
Change in benefit obligation, plan assets funded status and net periodic pension cost (benefit) [Table Text Block]	The following table presents information regarding this plan (in thousands): December 31, 2017 2016 Change in projected benefit obligation: Projected benefit obligation at beginning of year $ 34,964 $ 38,797 Interest cost 1,153 1,309 Actuarial loss (gain) 223 (55 ) Benefits paid (5,443 ) (5,087 ) Projected benefit obligation at end of year 1,2 $ 30,897 $ 34,964 Change in plan assets: Plan assets at fair value at beginning of year $ 41,769 $ 44,190 Actual return on plan assets 4,093 2,666 Benefits paid (5,443 ) (5,087 ) Plan assets at fair value at end of year $ 40,419 $ 41,769 Funded status of the plan $ 9,522 $ 6,805 Components of net periodic benefit: Interest cost $ 1,153 $ 1,309 Expected return on plan assets (2,041 ) (2,167 ) Other 184 (741 ) Net periodic benefit cost (credit) $ (704 ) $ (1,599 ) 1 Projected benefit obligation equals accumulated benefit obligation. 2 Projected benefit obligation is based on January 1 measurement date.
Valuation assumptions used [Table Text Block]	Weighted-average assumptions as of December 31: 2017 2016 Discount rate 3.30 % 3.43 % Expected return on plan assets 5.50 % 5.00 %
Expected future benefit payments [Table Text Block]	As of December 31, 2017 , expected future benefit payments related to the Pension Plan were as follows (in thousands): 2018 $ 2,831 2019 2,889 2020 2,763 2021 2,769 2022 2,813 Thereafter 25,501 Total estimated future benefit payments $ 39,566

Share-Based Compensation Plans

Share-Based Compensation Plans (Tables)	12 Months Ended
	Dec. 31, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Share-based Compensation, Stock Options, Activity [Table Text Block]	The following table presents stock options outstanding during 2017 , 2016 and 2015 under these plans (in thousands, except for per share data): Number Weighted- Average Exercise Price Aggregate Intrinsic Value Options outstanding at December 31, 2014 793,891 $ 49.05 $ 8,725 Options awarded — — Options exercised (286,678 ) 47.86 Options forfeited (22,304 ) 48.90 Options expired (4,874 ) 51.32 Options outstanding at December 31, 2015 480,035 49.75 4,821 Options awarded — — Options exercised (249,404 ) 47.60 Options forfeited (4,098 ) 55.44 Options expired (8,009 ) 53.43 Options outstanding at December 31, 2016 218,524 51.95 6,793 Options awarded — — Options exercised (99,556 ) 50.35 Options forfeited (624 ) 54.95 Options expired (793 ) 48.75 Options outstanding at December 31, 2017 117,551 $ 53.26 $ 4,592 Options vested at: December 31, 2015 243,395 $ 48.17 $ 2,829 December 31, 2016 93,117 46.22 3,429 December 31, 2017 51,286 48.62 2,241
Schedule of Nonvested Share Activity [Table Text Block]	The following represents a summary of the non-vested stock awards as of December 31, 2017 (in thousands): Shares Weighted Average Grant Date Fair Value Non-vested at January 1, 2015 688,611 Granted 312,755 $57.66 Vested (114,045 ) $50.15 Forfeited (96,212 ) $58.33 Non-vested at December 31, 2015 791,109 Granted 256,670 $55.35 Vested (213,941 ) $55.87 Forfeited (47,132 ) $57.86 Non-vested at December 31, 2016 786,706 Granted 177,807 $86.95 Vested (194,419 ) $63.07 Forfeited (102,991 ) $78.70 Non-vested at December 31, 2017 667,103

Related Parties Related Parties

Related Parties Related Parties (Tables)	12 Months Ended
	Dec. 31, 2017
Related Party Transactions [Abstract]
Schedule of Related Party Transactions [Table Text Block]	Activity in loans to related parties is summarized as follows (in thousands): Year Ended December 31, 2017 2016 Beginning balance $ 136,945 $ 594,225 Advances 1,559,291 884,511 Payments (1,585,865 ) (1,123,747 ) Adjustments 1 (125 ) (218,044 ) Ending balance $ 110,246 $ 136,945 1 Adjustments generally consist of changes in status as a related party.

Commitments and Contingent Li42

Commitments and Contingent Liabilities Variable Interest Entities (Tables)	12 Months Ended
	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Schedule of Variable Interest Entities [Table Text Block]	December 31, 2017 Loans Other Assets Other Liabilities Other Borrowings Non-controlling Interests Consolidated: Private equity funds $ — $ 14,783 $ — $ — $ 11,927 Tax credit entities 10,000 10,964 — 10,964 10,000 Other — 1,040 — — 1,040 Total consolidated $ 10,000 $ 26,787 $ — $ 10,964 $ 22,967 Unconsolidated: Tax credit entities $ 52,852 $ 153,506 $ 47,859 $ — $ — Other — 38,397 22,968 — — Total unconsolidated $ 52,852 $ 191,903 $ 70,827 $ — $ — December 31, 2016 Loans Other Other Other Non-controlling Consolidated: Private equity funds $ — $ 17,357 $ — $ — $ 13,237 Tax credit entities 10,000 11,585 — 10,964 10,000 Other — 29,783 3,189 1,092 8,266 Total consolidated $ 10,000 $ 58,725 $ 3,189 $ 12,056 $ 31,503 Unconsolidated: Tax credit entities $ 44,488 $ 143,715 $ 63,329 $ — $ — Other — 31,675 15,028 — — Total unconsolidated $ 44,488 $ 175,390 $ 78,357 $ — $ —

Earnings Per Share (Tables)

Earnings Per Share (Tables)	12 Months Ended
	Dec. 31, 2017
Earnings Per Share [Abstract]
Earnings Per Share [Table Text Block]	The following table presents the computation of basic and diluted earnings per share (dollars in thousands, except per share data): Year Ended 2017 2016 2015 Numerator: Net income attributable to BOK Financial Corp. shareholders $ 334,644 $ 232,668 $ 288,565 Less: Earnings allocated to participating securities 3,561 2,883 3,383 Numerator for basic earnings per share – income available to common shareholders 331,083 229,785 285,182 Effect of reallocating undistributed earnings of participating securities 2 1 3 Numerator for diluted earnings per share – income available to common shareholders $ 331,085 $ 229,786 $ 285,185 Denominator: Weighted average shares outstanding 65,440,832 65,901,110 68,397,215 Less: Participating securities included in weighted average shares outstanding 695,468 815,483 802,526 Denominator for basic earnings per common share 64,745,364 65,085,627 67,594,689 Dilutive effect of employee stock compensation plans 1 60,920 58,271 96,969 Denominator for diluted earnings per common share 64,806,284 65,143,898 67,691,658 Basic earnings per share $ 5.11 $ 3.53 $ 4.22 Diluted earnings per share $ 5.11 $ 3.53 $ 4.21 1 Excludes employee stock options with exercise prices greater than current market price. — — —

Shareholders' Equity (Tables)

Shareholders' Equity (Tables)	12 Months Ended
	Dec. 31, 2017
Stockholders' Equity Note [Abstract]
Summary of Regulatory Capital Levels [Table Text Block]	A summary of regulatory capital minimum requirements and levels follows (dollars in thousands): Minimum Capital Requirement Capital Conservation Buffer 1 Minimum Capital Requirement Including Capital Conservation Buffer December 31, 2017 December 31, 2016 Common Equity Tier 1 Capital (to Risk Weighted Assets): Consolidated 4.50% 2.50% 7.00% 3,074,981 12.05 % $ 2,834,532 11.21 % BOKF, NA 4.50% N/A 4.50% 2,870,694 11.34 % 2,609,450 10.65 % Mobank 2 4.50% N/A 4.50% N/A N/A 54,616 10.03 % Tier I Capital (to Risk Weighted Assets): Consolidated 6.00% 2.50% 8.50% $ 3,074,981 12.05 % $ 2,834,532 11.21 % BOKF, NA 6.00% N/A 6.00% 2,870,694 11.34 % 2,609,450 10.65 % Mobank 2 6.00% N/A 6.00% N/A N/A 54,616 10.03 % Total Capital (to Risk Weighted Assets): Consolidated 8.00% 2.50% 10.50% $ 3,455,709 13.54 % $ 3,238,323 12.81 % BOKF, NA 8.00% N/A 8.00% 3,105,117 12.27 % 2,866,949 11.70 % Mobank 2 8.00% N/A 8.00% N/A N/A 54,617 10.03 % Leverage (Tier I Capital to Average Assets): Consolidated 4.00% N/A 4.00% $ 3,074,981 9.31 % $ 2,834,532 8.72 % BOKF, NA 4.00% N/A 4.00% 2,870,694 8.73 % 2,609,450 8.11 % Mobank 2 4.00% N/A 4.00% N/A N/A 54,616 8.37 % 1 Capital conservation buffer is effective January 1, 2016 and is phased in through 2019. The phased in capital conservation buffer was 1.25% at December 31, 2017 and 0.625% at December 31, 2016 . The fully phased in requirement of 2.50% is included in the table above. 2 Missouri Bank and Trust Company of Kansas City dba Mobank was acquired by BOK Financial effective December 1, 2016 and was merged into BOKF, NA effective February 17, 2017.
Accumulated Other Comprehensive Income (Loss) [Table Text Block]	A rollforward of the components of accumulated other comprehensive income (loss) is included as follows (in thousands): Unrealized Gain (Loss) on Available for Sale Securities Investment Securities Transferred from AFS Employee Benefit Plans Loss on Effective Cash Flow Hedges Total Balance, December 31, 2014 $ 59,239 $ 376 $ (2,868 ) $ (74 ) $ 56,673 Net change in unrealized gain (loss) (48,607 ) — 1,804 — (46,803 ) Reclassification adjustments included in earnings: Interest revenue, Investment securities, Taxable securities — (503 ) — — (503 ) Interest expense, Subordinated debentures — — — 121 121 Net impairment losses recognized in earnings 1,819 — — — 1,819 Gain on available for sale securities, net (12,058 ) — — — (12,058 ) Other comprehensive income (loss), before income taxes (58,846 ) (503 ) 1,804 121 (57,424 ) Federal and state income tax 1 (22,891 ) (195 ) 701 47 (22,338 ) Other comprehensive income (loss), net of income taxes (35,955 ) (308 ) 1,103 74 (35,086 ) Balance, December 31, 2015 23,284 68 (1,765 ) — 21,587 Net change in unrealized gain (loss) (41,333 ) — (188 ) — (41,521 ) Reclassification adjustments included in earnings: Interest revenue, Investment securities, Taxable securities — (112 ) — — (112 ) Interest expense, Subordinated debentures — — — — — Net impairment losses recognized in earnings — — — — — Gain on available for sale securities, net (11,675 ) — — — (11,675 ) Other comprehensive income (loss), before income taxes (53,008 ) (112 ) (188 ) — (53,308 ) Federal and state income tax 1 (20,637 ) (44 ) (73 ) — (20,754 ) Other comprehensive income (loss), net of income taxes (32,371 ) (68 ) (115 ) — (32,554 ) Balance, December 31, 2016 (9,087 ) — (1,880 ) — (10,967 ) Net change in unrealized gain (loss) (28,170 ) — 2,018 — (26,152 ) Reclassification adjustments included in earnings: Interest revenue, Investment securities, Taxable securities — — — — — Interest expense, Subordinated debentures — — — — — Net impairment losses recognized in earnings — — — — — Gain on available for sale securities, net (4,428 ) — — — (4,428 ) Other comprehensive income (loss), before income taxes (32,598 ) — 2,018 — (30,580 ) Federal and state income tax 1 (12,708 ) — 785 — (11,923 ) Other comprehensive income (loss), net of income taxes (19,890 ) — 1,233 — (18,657 ) Reclassification of stranded accumulated other comprehensive loss related to tax reform (6,408 ) — (142 ) — (6,550 ) Balance, December 31, 2017 $ (35,385 ) $ — $ (789 ) $ — $ (36,174 ) 1 Calculated using 39% effective tax rate.

Reportable Segments (Tables)

Reportable Segments (Tables)	12 Months Ended
	Dec. 31, 2017
Segment Reporting [Abstract]
Reportable Segments [Table Text Block]	Reportable segments reconciliation to the Consolidated Financial Statements for the year ended December 31, 2017 is as follows (in thousands): Commercial Consumer Wealth Management Funds Management and Other BOK Financial Consolidated Net interest and dividend revenue from external sources $ 588,938 $ 96,360 $ 45,024 $ 111,379 $ 841,701 Net interest revenue (expense) from internal sources (84,290 ) 47,218 38,344 (1,272 ) — Net interest and dividend revenue 504,648 143,578 83,368 110,107 841,701 Provision for credit losses 13,881 4,783 (696 ) (24,968 ) (7,000 ) Net interest and dividend revenue after provision for credit losses 490,767 138,795 84,064 135,075 848,701 Other operating revenue 206,110 196,231 301,434 (8,681 ) 695,094 Other operating expense 226,334 224,323 246,626 328,234 1,025,517 Net direct contribution 470,543 110,703 138,872 (201,840 ) 518,278 Gain (loss) on financial instruments, net 52 (3,331 ) — 3,279 — Change in fair value of mortgage servicing rights — 172 — (172 ) — Gain (loss) on repossessed assets, net (2,681 ) 223 387 2,071 — Corporate expense allocations 33,958 67,761 40,562 (142,281 ) — Net income before taxes 433,956 40,006 98,697 (54,381 ) 518,278 Federal and state income taxes 168,809 15,562 38,393 (40,171 ) 182,593 Net income 265,147 24,444 60,304 (14,210 ) 335,685 Net income attributable to non-controlling interests — — — 1,041 1,041 Net income attributable to BOK Financial Corp. shareholders $ 265,147 $ 24,444 $ 60,304 $ (15,251 ) $ 334,644 Average assets $ 17,517,217 $ 8,956,713 $ 7,072,622 $ (599,058 ) $ 32,947,494 Reportable segments reconciliation to the Consolidated Financial Statements for the year ended December 31, 2016 is as follows (in thousands): Commercial Consumer Wealth Management Funds Management and Other BOK Financial Consolidated Net interest and dividend revenue from external sources $ 492,967 $ 85,998 $ 33,006 $ 135,257 $ 747,228 Net interest revenue (expense) from internal sources (58,781 ) 37,777 29,043 (8,039 ) — Net interest and dividend revenue 434,186 123,775 62,049 127,218 747,228 Provision for credit losses 32,959 4,927 (801 ) 27,915 65,000 Net interest and dividend revenue after provision for credit losses 401,227 118,848 62,850 99,303 682,228 Other operating revenue 195,521 224,802 283,222 (29,525 ) 674,020 Other operating expense 216,451 249,744 250,994 300,401 1,017,590 Net direct contribution 380,297 93,906 95,078 (230,623 ) 338,658 Gain (loss) on financial instruments, net 10 (26,252 ) (42 ) 26,284 — Change in fair value of mortgage servicing rights — (2,193 ) — 2,193 — Gain on repossessed assets, net 669 979 — (1,648 ) — Corporate expense allocations 35,760 66,411 42,378 (144,549 ) — Net income before taxes 345,216 29 52,658 (59,245 ) 338,658 Federal and state income taxes 134,289 11 20,484 (48,407 ) 106,377 Net income 210,927 18 32,174 (10,838 ) 232,281 Net loss attributable to non-controlling interests — — — (387 ) (387 ) Net income attributable to BOK Financial Corp. shareholders $ 210,927 $ 18 $ 32,174 $ (10,451 ) $ 232,668 Average assets $ 16,998,626 $ 8,722,372 $ 6,281,127 $ 276,277 $ 32,278,402 Reportable segments reconciliation to the Consolidated Financial Statements for the year ended December 31, 2015 is as follows (in thousands): Commercial Consumer Wealth Management Funds Management and Other BOK Financial Consolidated Net interest and dividend revenue from external sources $ 439,751 $ 84,848 $ 24,744 $ 154,011 $ 703,354 Net interest revenue (expense) from internal sources (52,313 ) 28,503 24,043 (233 ) — Net interest and dividend revenue 387,438 113,351 48,787 153,778 703,354 Provision for credit losses (6,748 ) 6,934 (1,083 ) 34,897 34,000 Net interest and dividend revenue after provision for credit losses 394,186 106,417 49,870 118,881 669,354 Other operating revenue 177,729 218,095 267,523 (4,867 ) 658,480 Other operating expense 202,804 203,070 228,664 261,653 896,191 Net direct contribution 369,111 121,442 88,729 (147,639 ) 431,643 Loss on financial instruments, net — (4,712 ) (204 ) 4,916 — Change in fair value of mortgage servicing rights — (4,853 ) — 4,853 — Gain on repossessed assets, net 708 916 — (1,624 ) — Corporate expense allocations 43,279 74,936 40,357 (158,572 ) — Net income before taxes 326,540 37,857 48,168 19,078 431,643 Federal and state income taxes 127,024 14,726 18,737 (21,103 ) 139,384 Net income 199,516 23,131 29,431 40,181 292,259 Net income attributable to non-controlling interests — — — 3,694 3,694 Net income attributable to BOK Financial Corp. shareholders $ 199,516 $ 23,131 $ 29,431 $ 36,487 $ 288,565 Average assets $ 16,284,527 $ 8,836,327 $ 5,444,483 $ 9,418 $ 30,574,755

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Fair Value Assets And Liabilities Measured On A Recurring Basis [Table Text Block]	The fair value of financial assets and liabilities that are measured on a recurring basis is as follows as of December 31, 2017 (in thousands): Total Quoted Prices in Active Markets for Identical Instruments Significant Other Observable Inputs Significant Unobservable Inputs Assets: Trading securities: U.S. government agency debentures $ 21,196 $ — $ 21,196 $ — U.S. agency residential mortgage-backed securities 392,673 — 392,673 — Municipal and other tax-exempt securities 13,559 — 13,559 — Asset-backed securities 23,885 — 23,885 — Other trading securities 11,363 — 11,363 — Total trading securities 462,676 — 462,676 — Available for sale securities: U.S. Treasury securities 1,000 1,000 — — Municipal and other tax-exempt securities 27,080 — 22,278 4,802 U.S. government agency residential mortgage-backed securities 5,309,152 — 5,309,152 — Privately issued residential mortgage-backed securities 93,221 — 93,221 — Commercial mortgage-backed securities guaranteed by U.S. government agencies 2,834,961 — 2,834,961 — Other debt securities 25,481 — 25,009 472 Perpetual preferred stock 15,767 — 15,767 — Equity securities and mutual funds 14,916 — 14,916 — Total available for sale securities 8,321,578 1,000 8,315,304 5,274 Fair value option securities – U.S. government agency residential mortgage-backed securities 755,054 — 755,054 — Residential mortgage loans held for sale 221,378 — 209,079 12,299 Mortgage servicing rights, net 1 252,867 — — 252,867 Derivative contracts, net of cash margin 2 220,502 8,179 212,323 — Liabilities: Derivative contracts, net of cash margin 2 171,963 — 171,963 — 1 A reconciliation of the beginning and ending fair value of mortgage servicing rights and disclosures of significant assumptions used to determine fair value are presented in Note 7 , Mortgage Banking Activities. 2 See Note 3 for detail of fair value of derivative contracts by contract type. Derivative contracts in a net asset position that were valued based on quoted prices in active markets or identical instruments (Level 1) are exchange-traded interest rate, energy and agricultural derivative contracts, net of cash margin. Derivative contracts in a net liability position that were valued using quoted prices in active markets for identical instruments (Level 1) are exchange-traded interest rate and energy derivative contracts, fully offset by cash margin. The fair value of financial assets and liabilities that are measured on a recurring basis is as follows as of December 31, 2016 (in thousands): Total Quoted Prices in Active Markets for Identical Instruments Significant Other Observable Inputs Significant Unobservable Inputs Assets: Trading securities: U.S. government agency debentures $ 6,234 $ — $ 6,234 $ — U.S. government agency residential mortgage-backed securities 310,067 — 310,067 — Municipal and other tax-exempt securities 14,427 — 14,427 — Asset-backed securities — — — — Other trading securities 6,900 — 6,900 — Total trading securities 337,628 — 337,628 — Available for sale securities: U.S. Treasury securities 999 999 — — Municipal and other tax-exempt securities 40,993 — 35,204 5,789 U.S. government agency residential mortgage-backed securities 5,460,386 — 5,460,386 — Privately issued residential mortgage-backed securities 115,535 — 115,535 — Commercial mortgage-backed securities guaranteed by U.S. government agencies 3,017,933 — 3,017,933 — Other debt securities 4,152 — — 4,152 Perpetual preferred stock 18,474 — 18,474 — Equity securities and mutual funds 18,357 3,495 14,862 — Total available for sale securities 8,676,829 4,494 8,662,394 9,941 Fair value option securities – U.S. government agency residential mortgage-backed securities 77,046 — 77,046 — Residential mortgage loans held for sale 301,897 — 290,280 11,617 Mortgage servicing rights, net 1 247,073 — — 247,073 Derivative contracts, net of cash margin 2 689,872 7,541 682,331 — Liabilities: Derivative contracts, net of cash margin 2 664,531 6,972 657,559 — 1 A reconciliation of the beginning and ending fair value of mortgage servicing rights and disclosures of significant assumptions used to determine fair value are presented in Note 7 , Mortgage Banking Activities. 2 See Note 3 for detail of fair value of derivative contracts by contract type. Derivative contracts in a net asset position that were valued based on quoted prices in active markets for identical instruments (Level 1) are exchange-traded interest rate and energy derivative contracts, net of cash margin. Derivative contracts in a net liability position that were valued using quoted prices in active markets for identical instruments based on quoted prices in active markets for identical instruments (Level 1) are exchange-traded interest rate, energy and agricultural derivative contracts, net of cash margin.
Fair Value Assets Measured On Recurring Basis Significant Unobservable Inputs [Table Text Block]	The following represents the changes related to assets measured at fair value on a recurring basis using significant unobservable inputs (in thousands): Available for Sale Securities Residential mortgage loans held for sale Municipal and other tax-exempt securities Other debt securities Balance, December 31, 2015 $ 9,610 $ 4,151 $ 7,874 Transfer to Level 3 from Level 2 1 — — 6,631 Purchases and capital calls — — — Redemptions and distributions (3,975 ) — — Proceeds from sales — — (2,540 ) Gain (loss) recognized in earnings: Mortgage banking revenue — — (348 ) Other comprehensive income (loss): Net change in unrealized gain (loss) 154 1 — Balance, December 31, 2016 5,789 4,152 11,617 Transfer to Level 3 from Level 2 1 — — 3,507 Purchases and capital calls — — — Redemptions and distributions (1,100 ) — — Proceeds from sales — (3,900 ) (2,944 ) Gain (loss) recognized in earnings: Mortgage banking revenue — — 119 Other comprehensive income (loss): Net change in unrealized gain (loss) 113 220 — Balance, December 31, 2017 $ 4,802 $ 472 $ 12,299 1 Recurring transfers to Level 3 from Level 2 consist of residential mortgage loans intended for sale to U.S. government agencies that fail to meet conforming standards.
Fair Value Assets Measured on Nonrecurring Basis [Table Text Block]	The following represents the carrying value of assets measured at fair value on a non-recurring basis and related losses recorded during the year. The carrying value represents only those assets with the balance sheet date for which the fair value was adjusted during the year: Carrying Value at December 31, 2017 Fair Value Adjustments for the Quoted Prices in Active Markets for Identical Instruments Significant Other Observable Inputs Significant Unobservable Inputs Gross charge-offs against allowance for loan losses Net losses and expenses of repossessed assets, net Impaired loans $ — $ 7,436 $ 7,626 $ 12,145 $ — Real estate and other repossessed assets — 3,483 5,481 — 6,372 Carrying Value at December 31, 2016 Fair Value Adjustments for the Quoted Prices in Active Markets for Identical Instruments Significant Other Observable Inputs Significant Unobservable Inputs Gross charge-offs against allowance for loan losses Net losses and expenses of repossessed assets, net Impaired loans $ — $ 539 $ 11,295 $ 7,594 $ — Real estate and other repossessed assets — 7,965 2,192 — 2,527
Fair Value Inputs, Assets, Quantitative Information [Table Text Block]	A summary of quantitative information about assets measured at fair value on a recurring basis using significant unobservable inputs (Level 3) as of December 31, 2017 follows (in thousands): Quantitative Information about Level 3 Recurring Fair Value Measurements Par Value Amortized Cost/Unpaid Principal Balance Fair Value Valuation Technique(s) Significant Unobservable Input Range (Weighted Average) Available for sale securities: Municipal and other tax-exempt securities $ 5,095 $ 5,068 $ 4,802 Discounted cash flows 1 Interest rate spread 6.60%-6.60% (6.60%) 2 92.25%-94.76% (93.75%) 3 Other debt securities 500 500 472 Discounted cash flows 1 Interest rate spread 6.85% - 6.85% (6.85%) 4 94.39% - 94.39% (94.39%) 3 Residential mortgage loans held for sale N/A 12,981 12,299 Quoted prices of loans sold in securitization transactions, with a liquidity discount applied Liquidity discount applied to the market value of mortgage loans qualifying for sale to U.S. government agencies 94.75% 1 Discounted cash flows developed using discount rates primarily based on reference to interest rate spreads for comparable securities of similar duration and credit rating as determined by the nationally-recognized rating agencies, adjusted for lack of trading volume. 2 Interest rate yields used to value investment grade tax-exempt securities represent a spread of 372 to 466 basis points over average yields for comparable tax-exempt securities. 3 Represents fair value as a percentage of par value. 4 Interest rate yields used to value investment grade taxable securities based on comparable short-term taxable securities which are generally yielding approximately 3% . A summary of quantitative information about Recurring Fair Value Measurements based on Significant Unobservable Inputs (Level 3) as of December 31, 2016 follows (in thousands): Quantitative Information about Level 3 Recurring Fair Value Measurements Par Value Amortized Cost 6 Fair Value Valuation Technique(s) Significant Unobservable Input Range (Weighted Average) Available for sale securities: Municipal and other tax-exempt securities $ 6,195 $ 6,163 $ 5,789 Discounted cash flows 1 Interest rate spread 5.91%-6.21% (6.16%) 2 90.00%-93.40% (92.20%) 3 Other debt securities 4,400 4,400 4,152 Discounted cash flows 1 Interest rate spread 6.01% - 6.26% (6.23%) 4 94.34% - 94.36% (94.36%) 3 Residential mortgage loans held for sale N/A 12,431 11,617 Quoted prices of loans sold in securitization transactions, with a liquidity discount applied Liquidity discount applied to the market value of mortgage loans qualifying for sale to U.S. government agencies 93.45% 1 Discounted cash flows developed using discount rates primarily based on reference to interest rate spreads for comparable securities of similar duration and credit rating as determined by the nationally-recognized rating agencies, adjusted for lack of trading volume. 2 Interest rate yields used to value investment grade tax-exempt securities represent a spread of 467 to 525 basis points over average yields for comparable tax-exempt securities. 3 Represents fair value as a percentage of par value. 4 Interest rate yields used to value investment grade taxable securities based on comparable short-term taxable securities which are generally yielding less than 1% . A summary of quantitative information about Non-recurring Fair Value Measurements based on Significant Unobservable Inputs (Level 3) as of December 31, 2017 follows (in thousands): Quantitative Information about Level 3 Non-recurring Fair Value Measurements Fair Value Valuation Technique(s) Significant Unobservable Input Range (Weighted Average) Impaired loans $ 7,626 Discounted cash flows Recoverable oil and gas reserves, forward-looking commodity prices and estimated operating costs 40% - 86% (59%) 1 Real estate and other repossessed assets 5,481 Discounted cash flows Recoverable oil and gas reserves, forward-looking commodity prices, estimated operating costs N/A 1 Represents fair value as a percentage of the unpaid principal balance. A summary of quantitative information about Non-recurring Fair Value Measurements based on Significant Unobservable Inputs (Level 3) as of December 31, 2016 follows (in thousands): Quantitative Information about Level 3 Non-recurring Fair Value Measurements Fair Value Valuation Technique(s) Significant Unobservable Input Range (Weighted Average) Impaired loans $ 11,295 Discounted cash flows Recoverable oil and gas reserves, forward-looking commodity prices and estimated operating costs 22% - 59% (57%) 1 Real estate and other repossessed assets 2,192 Appraised value, as adjusted Marketability adjustments off appraised value 2 70% - 87% (74%) 1 Represents fair value as a percentage of the unpaid principal balance. 2 Marketability adjustments include consideration of estimated costs to sell which is approximately 10% of the fair value.
Fair Value of Financial Instruments [Table Text Block]	The following table presents the carrying values and estimated fair values of all financial instruments, including those financial assets and liabilities that are not measured and reported at fair value on a recurring basis or non-recurring (dollars in thousands): December 31, 2017 Carrying Value Estimated Fair Value Quoted Prices in Active Markets for Identical Instruments (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Cash and due from banks $ 602,510 602,510 602,510 — — Interest-bearing cash and cash equivalents 1,714,544 1,714,544 1,714,544 — — Trading securities: U.S. government agency debentures 21,196 21,196 — 21,196 — U.S. government agency residential mortgage-backed securities 392,673 392,673 — 392,673 — Municipal and other tax-exempt securities 13,559 13,559 — 13,559 — Asset-backed securities 23,885 23,885 — 23,885 — Other trading securities 11,363 11,363 — 11,363 — Total trading securities 462,676 438,791 — 438,791 — Investment securities: Municipal and other tax-exempt securities 228,186 230,349 — 230,349 — U.S. government agency residential mortgage-backed securities 15,891 16,242 — 16,242 — Other debt securities 217,716 233,444 — 233,444 — Total investment securities 461,793 480,035 — 480,035 — Available for sale securities: U.S. Treasury securities 1,000 1,000 1,000 — — Municipal and other tax-exempt securities 27,080 27,080 — 22,278 4,802 U.S. government agency residential mortgage-backed securities 5,309,152 5,309,152 — 5,309,152 — Privately issued residential mortgage-backed securities 93,221 93,221 — 93,221 — Commercial mortgage-backed securities guaranteed by U.S. government agencies 2,834,961 2,834,961 — 2,834,961 — Other debt securities 25,481 25,481 — 25,009 472 Perpetual preferred stock 15,767 15,767 — 15,767 — Equity securities and mutual funds 14,916 14,916 — 14,916 — Total available for sale securities 8,321,578 8,321,578 1,000 8,315,304 5,274 Fair value option securities – U.S. government agency residential mortgage-backed securities 755,054 755,054 — 755,054 — Residential mortgage loans held for sale 221,378 221,378 — 208,946 12,432 Loans: Commercial 10,733,975 10,524,627 — — 10,524,627 Commercial real estate 3,479,987 3,428,733 — — 3,428,733 Residential mortgage 1,973,686 1,977,721 — — 1,977,721 Personal 965,776 956,706 — — 956,706 Total loans 17,153,424 16,887,787 — — 16,887,787 Allowance for loan losses (230,682 ) — — — — Loans, net of allowance 16,922,742 16,887,787 — — 16,887,787 Mortgage servicing rights 252,867 252,867 — — 252,867 Derivative instruments with positive fair value, net of cash margin 220,502 220,502 8,179 212,323 — Deposits with no stated maturity 19,962,889 19,962,889 — — 19,962,889 Time deposits 2,098,416 2,064,558 — — 2,064,558 Other borrowed funds 5,709,860 5,703,121 — — 5,703,121 Subordinated debentures 144,677 148,207 — 148,207 — Derivative instruments with negative fair value, net of cash margin 171,963 171,963 — 171,963 — December 31, 2016 Carrying Value Estimated Fair Value Quoted Prices in Active Markets for Identical Instruments (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Cash and due from banks $ 620,846 $ 620,846 620,846 — $ — Interest-bearing cash and cash equivalents 1,916,651 1,916,651 1,916,651 — — Trading securities: U.S. government agency debentures 6,234 6,234 — 6,234 — U.S. government agency residential mortgage-backed securities 310,067 310,067 — 310,067 — Municipal and other tax-exempt securities 14,427 14,427 — 14,427 — Asset-backed securities — — — — — Other trading securities 6,900 6,900 — 6,900 — Total trading securities 337,628 337,628 — 337,628 — Investment securities: Municipal and other tax-exempt securities 320,364 321,225 — 321,225 — U.S. government agency residential mortgage-backed securities 20,777 21,473 — 21,473 — Other debt securities 205,004 222,795 — 222,795 — Total investment securities 546,145 565,493 — 565,493 — Available for sale securities: U.S. Treasury securities 999 999 999 — — Municipal and other tax-exempt securities 40,993 40,993 — 35,204 5,789 U.S. government agency residential mortgage-backed securities 5,460,386 5,460,386 — 5,460,386 — Privately issued residential mortgage-backed securities 115,535 115,535 — 115,535 — Commercial mortgage-backed securities guaranteed by U.S. government agencies 3,017,933 3,017,933 — 3,017,933 — Other debt securities 4,152 4,152 — — 4,152 Perpetual preferred stock 18,474 18,474 — 18,474 — Equity securities and mutual funds 18,357 18,357 3,495 14,862 — Total available for sale securities 8,676,829 8,676,829 4,494 8,662,394 9,941 Fair value option securities – U.S. government agency residential mortgage-backed securities 77,046 77,046 — 77,046 — Residential mortgage loans held for sale 301,897 301,897 — 290,280 11,617 Loans: Commercial 10,390,824 10,437,016 — — 10,437,016 Commercial real estate 3,809,046 3,850,981 — — 3,850,981 Residential mortgage 1,949,832 2,025,159 — — 2,025,159 Personal 839,958 864,904 — — 864,904 Total loans 16,989,660 17,178,060 — — 17,178,060 Allowance for loan losses (246,159 ) — — — — Loans, net of allowance 16,743,501 17,178,060 — — 17,178,060 Mortgage servicing rights 247,073 247,073 — — 247,073 Derivative instruments with positive fair value, net of cash margin 689,872 689,872 7,541 682,331 — Deposits with no stated maturity 20,526,295 20,526,295 — — 20,526,295 Time deposits 2,221,800 2,218,303 — — 2,218,303 Other borrowed funds 5,572,662 5,556,327 — — 5,556,327 Subordinated debentures 144,640 128,903 — 128,903 — Derivative instruments with negative fair value, net of cash margin 664,531 664,531 6,972 657,559 —
Fair Value Inputs, Financial Instruments, Quantitative Information [Table Text Block]	Range of Contractual Yields Average Re-pricing (in years) Discount Rate Minimum Maximum Minimum Maximum December 31, 2017 Loans: Commercial 0.38 % 30.00 % 0.64 0.77 % 4.67 % Commercial real estate 0.38 % 18.00 % 0.80 1.04 % 4.41 % Residential mortgage 1.74 % 18.00 % 2.27 2.11 % 4.09 % Personal 1.18 % 21.00 % 0.23 0.56 % 4.81 % Time deposits 0.03 % 9.64 % 1.91 2.18 % 2.36 % Other borrowings 0.25 % 3.49 % 0.00 1.33 % 4.04 % Subordinated debentures 5.38 % 5.38 % 16.79 4.61 % 4.61 % December 31, 2016 Loans: Commercial 0.38 % 30.00 % 0.70 0.64 % 4.60 % Commercial real estate 0.38 % 18.00 % 0.71 0.94 % 4.27 % Residential mortgage 1.74 % 18.00 % 2.27 1.71 % 4.26 % Personal 0.25 % 21.00 % 0.40 1.03 % 4.59 % Time deposits 0.02 % 9.65 % 1.96 1.57 % 2.00 % Other borrowings 0.25 % 3.50 % 0.00 0.55 % 3.22 % Subordinated debentures 5.38 % 5.38 % 16.86 6.11 % 6.11 %

Parent Company Only Financial47

Parent Company Only Financial Statements Parent Company Only Financial Statements (Tables)	12 Months Ended
	Dec. 31, 2017
Condensed Financial Information of Parent Company Only Disclosure [Abstract]
Condensed Balance Sheet [Table Text Block]	Balance Sheets (In thousands) December 31, 2017 2016 Assets Cash and cash equivalents $ 205,876 $ 163,418 Available for sale securities 16,185 19,234 Investment in bank subsidiaries 3,255,912 3,067,595 Investment in non-bank subsidiaries 170,966 177,068 Other assets 4,065 4,865 Total assets $ 3,653,004 $ 3,432,180 Liabilities and Shareholders’ Equity Liabilities: Other liabilities $ 12,960 $ 5,469 Other borrowings – Trust preferred debt — 7,217 Subordinated debentures 144,677 144,640 Total liabilities 157,637 157,326 Shareholders’ equity: Common stock 4 4 Capital surplus 1,035,895 1,006,535 Retained earnings 3,048,487 2,823,334 Treasury stock (552,845 ) (544,052 ) Accumulated other comprehensive loss (36,174 ) (10,967 ) Total shareholders’ equity 3,495,367 3,274,854 Total liabilities and shareholders’ equity $ 3,653,004 $ 3,432,180
Condensed Income Statement [Table Text Block]	Statements of Earnings (In thousands) Year Ended December 31, 2017 2016 2015 Dividends, interest and fees received from bank subsidiaries $ 150,149 $ 15,237 $ 150,308 Dividends, interest and fees received from non-bank subsidiaries 17,500 25,923 — Other revenue 936 1,612 1,279 Total revenue 168,585 42,772 151,587 Interest expense 8,239 4,182 131 Other operating expense 2,014 1,978 2,242 Total expense 10,253 6,160 2,373 Income before taxes and equity in undistributed income of subsidiaries 158,332 36,612 149,214 Federal and state income taxes (4,305 ) (1,920 ) (375 ) Income before equity in undistributed income of subsidiaries 162,637 38,532 149,589 Equity in undistributed income of bank subsidiaries 181,552 216,120 134,045 Equity in undistributed income of non-bank subsidiaries (9,545 ) (21,984 ) 4,931 Net income attributable to BOK Financial Corp. shareholders $ 334,644 $ 232,668 $ 288,565
Condensed Cash Flow Statement [Table Text Block]	Statements of Cash Flows (In thousands) Year Ended December 31, 2017 2016 2015 Cash Flows From Operating Activities: Net income $ 334,644 $ 232,668 $ 288,565 Adjustments to reconcile net income to net cash provided by operating activities: Equity in undistributed income of bank subsidiaries (181,552 ) (216,120 ) (134,045 ) Equity in undistributed income of non-bank subsidiaries 9,545 21,984 (4,931 ) Change in other assets 12 (2,933 ) 49 Change in other liabilities 7,457 (1,285 ) (2,818 ) Net cash provided by operating activities 170,106 34,314 146,820 Cash Flows From Investing Activities: Proceeds from sales of available for sale securities 3,000 1,632 4,760 Investment in subsidiaries (4,355 ) (26,000 ) (41,969 ) Acquisitions, net of cash acquired — (105,520 ) — Net cash used in investing activities (1,355 ) (129,888 ) (37,209 ) Cash Flows From Financing Activities: Net change in other borrowings (7,217 ) — — Issuance of subordinated debentures, net of issuance costs — 144,615 — Issuance of common and treasury stock, net 4,368 12,455 6,711 Dividends paid (116,041 ) (113,455 ) (115,281 ) Repurchase of common stock (7,403 ) (66,792 ) (229,540 ) Net cash used in financing activities (126,293 ) (23,177 ) (338,110 ) Net increase (decrease) in cash and cash equivalents 42,458 (118,751 ) (228,499 ) Cash and cash equivalents at beginning of period 163,418 282,169 510,668 Cash and cash equivalents at end of period $ 205,876 $ 163,418 $ 282,169 Cash paid for interest $ 6,211 $ 4,127 $ 131

Significant Accounting Polici48

Significant Accounting Policies Goodwill and Intangible Assets (Details)	12 Months Ended
	Dec. 31, 2017
Minimum [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life	3 years
Maximum [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life	20 years

Significant Accounting Polici49

Significant Accounting Policies Cash Equivalents (Details)	12 Months Ended
	Dec. 31, 2017
Cash and Cash Equivalents [Abstract]
Maturity of Federal Funds Sold Considered Cash Equivalents	1 day
Maturity of Resell Agreement Considered Cash Equivalents, Minimum	1 day
Maturity of Resell Agreements Considered Cash Equivalents, Maximum	30 days

Significant Accounting Polici50

Significant Accounting Policies Loans (Details)	12 Months Ended
	Dec. 31, 2017
Loans [Abstract]
Loans, Number of Days Past Due for a Non-Risk Graded Loan to be Placed on Nonaccruing Status	90 days
Loans, Number of Days After Notification of Chapter 7 Bankruptcy Non-Risk Graded Loan is Placed on Nonaccruing Status	60 days
Loans, Minimum Number of Days After Which Past Due Non-Risk Graded Loans Are Charged Off	60 days
Loans, Maximum Number of Days After Which Past Due Non-Risk Graded Loans Are Charged Off	180 days
Loans, Number of Days After Notification of Chapter 7 Bankruptcy Non-Risk Graded Loan is Charged Off	60 days

Significant Accounting Polici51

Significant Accounting Policies Premises and Equipment (Details)	12 Months Ended
	Dec. 31, 2017
Buildings and improvements | Minimum [Member]
Premises and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	5 years
Buildings and improvements | Maximum [Member]
Premises and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	40 years
Software and Software Development Costs [Member] | Minimum [Member]
Premises and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	3 years
Software and Software Development Costs [Member] | Maximum [Member]
Premises and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	10 years
Furniture and equipment | Minimum [Member]
Premises and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	3 years
Furniture and equipment | Maximum [Member]
Premises and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	10 years

Significant Accounting Polici52

Significant Accounting Policies Share-Based Compensation (Details)	12 Months Ended
	Dec. 31, 2017
Stock Options [Member]
Share-based Compensation Arrangements by Share-based Payment Award [Line Items]
Vesting period (in years)	7 years
Non-vested Common Stock [Member]
Share-based Compensation Arrangements by Share-based Payment Award [Line Items]
Vesting period (in years)	3 years
Share-based Compensation Arrangement by Share-based Payment Award, Award Required Holding Period	2 years

Significant Accounting Polici53

Significant Accounting Policies Newly Adopted and Pending Accounting Pronouncements (Details) $ in Millions	12 Months Ended
	Dec. 31, 2017USD ($)
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Interchange fees related to transaction card processing revenue	$ 39
Increase of reported right of use assets and liabilities, minimum	100
Increase of reported right of use assets and liabilities maximum	$ 150

Significant Accounting Polici54

Significant Accounting Policies Reclassification (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Accounting Policies [Abstract]
Prior Period Reclassification Adjustment	$ 19.3	$ 19

Trading Securities (Details)

Trading Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Schedule of Trading Securities [Line Items]
Trading Securities, Fair Value	$ 462,676	$ 337,628
Trading Securities, Net Unrealized Gain (Loss)	(448)	738
U.S. government agency debentures [Member]
Schedule of Trading Securities [Line Items]
Trading Securities, Fair Value	21,196	6,234
Trading Securities, Net Unrealized Gain (Loss)	8	(4)
U.S. government agency residential mortgage-backed securities [Member]
Schedule of Trading Securities [Line Items]
Trading Securities, Fair Value	392,673	310,067
Trading Securities, Net Unrealized Gain (Loss)	(517)	635
Municipal and other tax-exempt securities [Member]
Schedule of Trading Securities [Line Items]
Trading Securities, Fair Value	13,559	14,427
Trading Securities, Net Unrealized Gain (Loss)	83	50
Asset-backed Securities [Member]
Schedule of Trading Securities [Line Items]
Trading Securities, Fair Value	23,885	0
Trading Securities, Net Unrealized Gain (Loss)	(26)	0
Other trading securities [Member]
Schedule of Trading Securities [Line Items]
Trading Securities, Fair Value	11,363	6,900
Trading Securities, Net Unrealized Gain (Loss)	$ 4	$ 57

Investment (Held-to-Maturity) S

Investment (Held-to-Maturity) Securities (Details) $ in Thousands		12 Months Ended
		Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)
Schedule of Investment (Held-to-Maturity) Securities [Line Items]
Investment securities		$ 461,793	$ 546,145
Investment Securities, Fair Value		480,035	565,493
Investment Securities, Gross Unrealized Gain		20,508	21,154
Investment Securities, Gross Unrealized Loss		(2,266)	(1,806)
Investment Securities, Debt Maturities, Carrying Value [Abstract]
Investment Securities, Debt Maturities, Carrying Value		461,793	546,145
Investment Securities, Debt Maturities, Fair Value, Rolling Maturity [Abstract]
Investment Securities, Fair Value		$ 480,035	565,493
Investment Securities, Debt Maturities, Nominal Yield [Abstract]
Investment Securities, Debt Maturities, Nominal Yield		3.93%
Investment Securities, Pledged as Collateral [Abstract]
Investment Securities, Pledged as Collateral, Carrying Value		$ 226,852	322,208
Investment Securities, Pledged as Collateral, Fair Value		$ 229,429	$ 323,808
Investment Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract]
Investment Securities, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Securities		150	193
Investment Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Investment Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value		$ 166,051	$ 236,070
Investment Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value		12,265	5,188
Investment Securities, Continuous Unrealized Loss Position, Fair Value		178,316	241,258
Investment Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Investment Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses		1,881	1,709
Investment Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses		385	97
Investment Securities, Continuous Unrealized Loss Position, Accumulated Loss		2,266	1,806
Fixed maturity securities [Member]
Investment Securities, Debt Maturities, Carrying Value [Abstract]
Investment Securities, Debt Maturities, Less than One Year, Carrying Value		116,565
Investment Securities, Debt Maturities, One to Five Years, Carrying Value		126,240
Investment Securities, Debt Maturities, Six to Ten Years, Carrying Value		150,162
Investment Securities, Debt Maturities, Over Ten Years, Carrying Value		52,935
Held-to-maturity Securities, Debt Maturities, Single Maturity Date, Carrying Value		445,902
Investment Securities, Debt Maturities, Fair Value, Rolling Maturity [Abstract]
Investment Securities, Debt Maturities, Less than One Year, Fair Value		116,472
Investment Securities, Debt Maturities, One to Five Years, Fair Value		128,294
Investment Securities, Debt Maturities, Six to Ten Years, Fair Value		165,055
Investment Securities, Debt Maturities, Over Ten Years, Fair Value		53,972
Investment Securities, Debt Maturities, Single Maturity Date, Fair value		$ 463,793
Investment Securities, Debt Maturities, Nominal Yield [Abstract]
Investment Securities, Debt Maturities, Less Than One Year, Nominal Yield		2.11%
Investment Securities, Debt Maturities, One to Five Years, Nominal Yield		3.32%
Investment Securities, Debt Maturities, Six to Ten Years, Nominal Yield		5.63%
Investment Securities, Debt Maturities, Over Ten Years, Nominal Yield		4.92%
Investment Securities, Debt Maturities, Nominal Yield		3.97%
Investment Securities, Debt Maturities, Weighted Average Maturity	[1]	4.83
Municipal and other tax-exempt securities [Member]
Schedule of Investment (Held-to-Maturity) Securities [Line Items]
Investment securities		$ 228,186	320,364
Investment Securities, Fair Value		230,349	321,225
Investment Securities, Gross Unrealized Gain		2,967	2,272
Investment Securities, Gross Unrealized Loss		(804)	(1,411)
Investment Securities, Debt Maturities, Carrying Value [Abstract]
Investment Securities, Debt Maturities, Less than One Year, Carrying Value		102,569
Investment Securities, Debt Maturities, One to Five Years, Carrying Value		74,738
Investment Securities, Debt Maturities, Six to Ten Years, Carrying Value		14,929
Investment Securities, Debt Maturities, Over Ten Years, Carrying Value		35,950
Held-to-maturity Securities, Debt Maturities, Single Maturity Date, Carrying Value		228,186
Investment Securities, Debt Maturities, Carrying Value		228,186	320,364
Investment Securities, Debt Maturities, Fair Value, Rolling Maturity [Abstract]
Investment Securities, Debt Maturities, Less than One Year, Fair Value		102,414
Investment Securities, Debt Maturities, One to Five Years, Fair Value		74,467
Investment Securities, Debt Maturities, Six to Ten Years, Fair Value		15,538
Investment Securities, Debt Maturities, Over Ten Years, Fair Value		37,930
Investment Securities, Debt Maturities, Single Maturity Date, Fair value		230,349
Investment Securities, Fair Value		$ 230,349	$ 321,225
Investment Securities, Debt Maturities, Nominal Yield [Abstract]
Investment Securities, Debt Maturities, Less Than One Year, Nominal Yield	[2]	1.82%
Investment Securities, Debt Maturities, One to Five Years, Nominal Yield	[2]	2.34%
Investment Securities, Debt Maturities, Six to Ten Years, Nominal Yield	[2]	5.06%
Investment Securities, Debt Maturities, Over Ten Years, Nominal Yield	[2]	5.19%
Investment Securities, Debt Maturities, Nominal Yield	[2]	2.73%
Investment Securities, Debt Maturities, Weighted Average Maturity	[1]	3.51
Investment Securities, Debt Maturities, Effective tax rate for nominal yield calculation		39.00%
Investment Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract]
Investment Securities, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Securities		100	151
Investment Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Investment Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value		$ 145,960	$ 219,892
Investment Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value		5,833	4,333
Investment Securities, Continuous Unrealized Loss Position, Fair Value		151,793	224,225
Investment Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Investment Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses		643	1,316
Investment Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses		161	95
Investment Securities, Continuous Unrealized Loss Position, Accumulated Loss		804	1,411
Other debt securities [Member]
Schedule of Investment (Held-to-Maturity) Securities [Line Items]
Investment securities		217,716	205,004
Investment Securities, Fair Value		233,444	222,795
Investment Securities, Gross Unrealized Gain		17,095	18,115
Investment Securities, Gross Unrealized Loss		(1,367)	(324)
Investment Securities, Debt Maturities, Carrying Value [Abstract]
Investment Securities, Debt Maturities, Less than One Year, Carrying Value		13,996
Investment Securities, Debt Maturities, One to Five Years, Carrying Value		51,502
Investment Securities, Debt Maturities, Six to Ten Years, Carrying Value		135,233
Investment Securities, Debt Maturities, Over Ten Years, Carrying Value		16,985
Held-to-maturity Securities, Debt Maturities, Single Maturity Date, Carrying Value		217,716
Investment Securities, Debt Maturities, Carrying Value		217,716	205,004
Investment Securities, Debt Maturities, Fair Value, Rolling Maturity [Abstract]
Investment Securities, Debt Maturities, Less than One Year, Fair Value		14,058
Investment Securities, Debt Maturities, One to Five Years, Fair Value		53,827
Investment Securities, Debt Maturities, Six to Ten Years, Fair Value		149,517
Investment Securities, Debt Maturities, Over Ten Years, Fair Value		16,042
Investment Securities, Debt Maturities, Single Maturity Date, Fair value		233,444
Investment Securities, Fair Value		$ 233,444	$ 222,795
Investment Securities, Debt Maturities, Nominal Yield [Abstract]
Investment Securities, Debt Maturities, Less Than One Year, Nominal Yield		4.24%
Investment Securities, Debt Maturities, One to Five Years, Nominal Yield		4.75%
Investment Securities, Debt Maturities, Six to Ten Years, Nominal Yield		5.69%
Investment Securities, Debt Maturities, Over Ten Years, Nominal Yield		4.36%
Investment Securities, Debt Maturities, Nominal Yield		5.27%
Investment Securities, Debt Maturities, Weighted Average Maturity	[1]	6.23
Investment Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract]
Investment Securities, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Securities		49	41
Investment Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Investment Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value		$ 20,091	$ 11,820
Investment Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value		3,076	855
Investment Securities, Continuous Unrealized Loss Position, Fair Value		23,167	12,675
Investment Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Investment Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses		1,238	322
Investment Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses		129	2
Investment Securities, Continuous Unrealized Loss Position, Accumulated Loss		1,367	324
U.S. government agency residential mortgage-backed securities [Member] | Other [Member]
Schedule of Investment (Held-to-Maturity) Securities [Line Items]
Investment securities		15,891	20,777
Investment Securities, Fair Value		16,242	21,473
Investment Securities, Gross Unrealized Gain		446	767
Investment Securities, Gross Unrealized Loss		(95)	(71)
Investment Securities, Debt Maturities, Carrying Value [Abstract]
Held-to-maturity Securities, Debt Maturities, without Single Maturity Date, Carrying value		15,891
Investment Securities, Debt Maturities, Carrying Value		15,891	20,777
Investment Securities, Debt Maturities, Fair Value, Rolling Maturity [Abstract]
Investment Securities, Debt Maturities, without Single Maturity Date, Fair value		16,242
Investment Securities, Fair Value		$ 16,242	$ 21,473
Investment Securities, Debt Maturities, Nominal Yield [Abstract]
Investment Securities, Debt Maturities, Nominal Yield	[3]	2.76%
Investment Securities, Debt Maturities, Average Expected Life of Mortgage-backed Securities		4 years 292 days
Investment Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract]
Investment Securities, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Securities		1	1
Investment Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Investment Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value		$ 0	$ 4,358
Investment Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value		3,356	0
Investment Securities, Continuous Unrealized Loss Position, Fair Value		3,356	4,358
Investment Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Investment Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses		0	71
Investment Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses		95	0
Investment Securities, Continuous Unrealized Loss Position, Accumulated Loss		$ 95	$ 71
[1]	Expected maturities may differ from contractual maturities because borrowers may have the right to call or prepay obligations with or without penalty.
[2]	Calculated on a taxable equivalent basis using a 39% effective tax rate.
[3]	The nominal yield on residential mortgage-backed securities is based upon prepayment assumptions at the purchase date. Actual yields earned may differ significantly based upon actual prepayments. See Quarterly Financial Summary - Unaudited for current yields on the investment securities portfolio.

Available for Sale Securities (

Available for Sale Securities (Details)		12 Months Ended
		Dec. 31, 2017USD ($)		Dec. 31, 2016USD ($)		Dec. 31, 2015USD ($)
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost		$ 8,369,075,000		$ 8,691,728,000
Available-for-sale Securities, Fair Value		8,321,578,000		8,676,829,000
Available-for-sale Securities, Gross Unrealized Gain		41,519,000		60,165,000
Available-for-sale Securities, Gross Unrealized Loss		(88,625,000)		(74,846,000)
Available-for-Sale Securities, Other Than Temporary Impairments		$ (391,000)		(218,000)
Available-for-sale Securities, Debt Maturities, Nominal Yield [Abstract]
Available-for-sale Securities, Debt Maturities, Nominal Yield		2.02%
Available-for-sale Securities, Gross Realized Gain (Loss), Disclosures [Abstract]
Available-for-sale Securities, Proceeds		$ 1,309,215,000		899,381,000		$ 1,600,380,000
Available-for-sale Securities, Gross realized gains		10,223,000		11,696,000		15,849,000
Available-for-sale Securities, Gross realized losses		(5,795,000)		(21,000)		(3,791,000)
Available-for-sale Securites, Related federal and state income tax expense		1,722,000		4,542,000		$ 4,691,000
Available-for-sale Securities, Pledged as Collateral [Abstract]
Available-for-sale Securities, Pledged As Collateral, Amortized cost		7,151,468,000		7,353,116,000
Available-for-sale Securities, Pledged As Collateral, Fair value		$ 7,089,346,000		$ 7,327,470,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Securities		534		488
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value		$ 3,773,942,000		$ 5,231,605,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value		2,118,360,000		178,249,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		5,892,302,000		5,409,854,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss		30,648,000		70,818,000
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss		58,368,000		4,246,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss		89,016,000		75,064,000
Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net [Abstract]
Available-for-sale Securities, Other than Temporary Impairment Losses		0		0
Fixed maturity securities [Member]
Available-for-sale Securities, Debt Maturities, Amortized Cost, Rolling Maturity [Abstract]
Available-for-sale Securities, Debt Maturities, Less than One Year, Amortized Cost		32,750,000
Available-for-sale Securities, Debt Maturities, One to Five Years, Amortized Cost		973,291,000
Available-for-sale Securities, Debt Maturities, Six to Ten Years, Amortized Cost		1,604,465,000
Available-for-sale Securities, Debt Maturities, Over Ten Years, Amortized Cost		302,061,000
Available-for-sale Securities, Debt Maturities, Single Maturity Date, Amortized Cost Basis		2,912,567,000
Available-for-sale Securities, Debt Maturities, Fair Value, Rolling Maturity [Abstract]
Available-for-sale Securities, Debt Maturities, Less Than One Year, Fair Value		32,689,000
Available-for-sale Securities, Debt Maturities, One to Five Years, Fair Value		967,910,000
Available-for-sale Securities, Debt Maturities, Six to Ten Years, Fair Value		1,590,107,000
Available-for-sale Securities, Debt Maturities, Over Ten Years, Fair Value		297,816,000
Available-for-sale Securities, Debt Maturities, Single Maturity Date, Fair value		$ 2,888,522,000
Available-for-sale Securities, Debt Maturities, Nominal Yield [Abstract]
Available-for-sale Securities, Debt Maturities, Less than One Year, Nominal Yield		2.01%
Available-for-sale Securities, Debt Maturities, One to Five Years, Nominal Yield		1.94%
Available-for-sale Securities, Debt Maturities, Six to Ten Years, Nominal Yield		2.03%
Available-for-sale Securities, Debt Maturities, Greater Than Ten Years, Nominal Yield		2.01%
Available-for-sale Securities, Debt Maturities, Nominal Yield		2.00%
Available-for-sale Securities, Debt Maturities, Weighted Average Maturity	[1]	7.25
U.S. Treasury securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost		$ 1,000,000		1,000,000
Available-for-sale Securities, Fair Value		1,000,000		999,000
Available-for-sale Securities, Gross Unrealized Gain		0		0
Available-for-sale Securities, Gross Unrealized Loss		0		(1,000)
Available-for-Sale Securities, Other Than Temporary Impairments		0		$ 0
Available-for-sale Securities, Debt Maturities, Amortized Cost, Rolling Maturity [Abstract]
Available-for-sale Securities, Debt Maturities, Less than One Year, Amortized Cost		1,000,000
Available-for-sale Securities, Debt Maturities, One to Five Years, Amortized Cost		0
Available-for-sale Securities, Debt Maturities, Six to Ten Years, Amortized Cost		0
Available-for-sale Securities, Debt Maturities, Over Ten Years, Amortized Cost		0
Available-for-sale Securities, Debt Maturities, Single Maturity Date, Amortized Cost Basis		1,000,000
Available-for-sale Securities, Debt Maturities, Fair Value, Rolling Maturity [Abstract]
Available-for-sale Securities, Debt Maturities, Less Than One Year, Fair Value		1,000,000
Available-for-sale Securities, Debt Maturities, One to Five Years, Fair Value		0
Available-for-sale Securities, Debt Maturities, Six to Ten Years, Fair Value		0
Available-for-sale Securities, Debt Maturities, Over Ten Years, Fair Value		0
Available-for-sale Securities, Debt Maturities, Single Maturity Date, Fair value		$ 1,000,000
Available-for-sale Securities, Debt Maturities, Nominal Yield [Abstract]
Available-for-sale Securities, Debt Maturities, Less than One Year, Nominal Yield		0.87%
Available-for-sale Securities, Debt Maturities, One to Five Years, Nominal Yield		0.00%
Available-for-sale Securities, Debt Maturities, Six to Ten Years, Nominal Yield		0.00%
Available-for-sale Securities, Debt Maturities, Greater Than Ten Years, Nominal Yield		0.00%
Available-for-sale Securities, Debt Maturities, Nominal Yield		0.87%
Available-for-sale Securities, Debt Maturities, Weighted Average Maturity	[1]	0.04
Available-for-sale Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Securities		0		1
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value		$ 0		$ 999,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value		0		0
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		0		999,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss		0		1,000
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss		0		0
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss		0		1,000
Municipal and other tax-exempt securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost		27,182,000		41,050,000
Available-for-sale Securities, Fair Value		27,080,000		40,993,000
Available-for-sale Securities, Gross Unrealized Gain		181,000		343,000
Available-for-sale Securities, Gross Unrealized Loss		(283,000)		(400,000)
Available-for-Sale Securities, Other Than Temporary Impairments		0		$ 0
Available-for-sale Securities, Debt Maturities, Amortized Cost, Rolling Maturity [Abstract]
Available-for-sale Securities, Debt Maturities, Less than One Year, Amortized Cost		9,008,000
Available-for-sale Securities, Debt Maturities, One to Five Years, Amortized Cost		2,680,000
Available-for-sale Securities, Debt Maturities, Six to Ten Years, Amortized Cost		0
Available-for-sale Securities, Debt Maturities, Over Ten Years, Amortized Cost		15,494,000
Available-for-sale Securities, Debt Maturities, Single Maturity Date, Amortized Cost Basis		27,182,000
Available-for-sale Securities, Debt Maturities, Fair Value, Rolling Maturity [Abstract]
Available-for-sale Securities, Debt Maturities, Less Than One Year, Fair Value		9,022,000
Available-for-sale Securities, Debt Maturities, One to Five Years, Fair Value		2,811,000
Available-for-sale Securities, Debt Maturities, Six to Ten Years, Fair Value		0
Available-for-sale Securities, Debt Maturities, Over Ten Years, Fair Value		15,247,000
Available-for-sale Securities, Debt Maturities, Single Maturity Date, Fair value		$ 27,080,000
Available-for-sale Securities, Debt Maturities, Nominal Yield [Abstract]
Available-for-sale Securities, Debt Maturities, Less than One Year, Nominal Yield	[2]	3.45%
Available-for-sale Securities, Debt Maturities, One to Five Years, Nominal Yield	[2]	6.04%
Available-for-sale Securities, Debt Maturities, Six to Ten Years, Nominal Yield	[2]	0.00%
Available-for-sale Securities, Debt Maturities, Greater Than Ten Years, Nominal Yield	[2],[3]	2.26%
Available-for-sale Securities, Debt Maturities, Nominal Yield	[2]	3.03%
Available-for-sale Securities, Debt Maturities, Weighted Average Maturity	[1]	9.15
Available-for-sale Securities, Debt Maturities, Effective tax rate for nominal yield calculation		39.00%
Available-for-sale Securities, Debt Maturities, Number of days for interest rates to reset		35 days
Available-for-sale Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Securities		19		24
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value		$ 12,765,000		$ 15,666,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value		4,802,000		4,689,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		17,567,000		20,355,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss		18,000		22,000
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss		265,000		378,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss		283,000		400,000
Commercial mortgage-backed securities guaranteed by U.S. government agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost		2,858,885,000		3,035,750,000
Available-for-sale Securities, Fair Value		2,834,961,000		3,017,933,000
Available-for-sale Securities, Gross Unrealized Gain		1,963,000		5,472,000
Available-for-sale Securities, Gross Unrealized Loss		(25,887,000)		(23,289,000)
Available-for-Sale Securities, Other Than Temporary Impairments		0		$ 0
Available-for-sale Securities, Debt Maturities, Amortized Cost, Rolling Maturity [Abstract]
Available-for-sale Securities, Debt Maturities, Less than One Year, Amortized Cost		22,742,000
Available-for-sale Securities, Debt Maturities, One to Five Years, Amortized Cost		970,611,000
Available-for-sale Securities, Debt Maturities, Six to Ten Years, Amortized Cost		1,604,465,000
Available-for-sale Securities, Debt Maturities, Over Ten Years, Amortized Cost		261,067,000
Available-for-sale Securities, Debt Maturities, Single Maturity Date, Amortized Cost Basis		2,858,885,000
Available-for-sale Securities, Debt Maturities, Fair Value, Rolling Maturity [Abstract]
Available-for-sale Securities, Debt Maturities, Less Than One Year, Fair Value		22,667,000
Available-for-sale Securities, Debt Maturities, One to Five Years, Fair Value		965,099,000
Available-for-sale Securities, Debt Maturities, Six to Ten Years, Fair Value		1,590,107,000
Available-for-sale Securities, Debt Maturities, Over Ten Years, Fair Value		257,088,000
Available-for-sale Securities, Debt Maturities, Single Maturity Date, Fair value		$ 2,834,961,000
Available-for-sale Securities, Debt Maturities, Nominal Yield [Abstract]
Available-for-sale Securities, Debt Maturities, Less than One Year, Nominal Yield		1.49%
Available-for-sale Securities, Debt Maturities, One to Five Years, Nominal Yield		1.93%
Available-for-sale Securities, Debt Maturities, Six to Ten Years, Nominal Yield		2.03%
Available-for-sale Securities, Debt Maturities, Greater Than Ten Years, Nominal Yield		2.03%
Available-for-sale Securities, Debt Maturities, Nominal Yield		1.99%
Available-for-sale Securities, Debt Maturities, Weighted Average Maturity	[1]	7.17
Available-for-sale Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Securities		185		171
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value		$ 1,465,703,000		$ 1,904,584,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value		652,296,000		38,875,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		2,117,999,000		1,943,459,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss		11,824,000		22,987,000
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss		14,063,000		302,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss		25,887,000		23,289,000
Other debt securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost		25,500,000		4,400,000
Available-for-sale Securities, Fair Value		25,481,000		4,152,000
Available-for-sale Securities, Gross Unrealized Gain		50,000		0
Available-for-sale Securities, Gross Unrealized Loss		(69,000)		(248,000)
Available-for-Sale Securities, Other Than Temporary Impairments		0		$ 0
Available-for-sale Securities, Debt Maturities, Amortized Cost, Rolling Maturity [Abstract]
Available-for-sale Securities, Debt Maturities, Less than One Year, Amortized Cost		0
Available-for-sale Securities, Debt Maturities, One to Five Years, Amortized Cost		0
Available-for-sale Securities, Debt Maturities, Six to Ten Years, Amortized Cost		0
Available-for-sale Securities, Debt Maturities, Over Ten Years, Amortized Cost		25,500,000
Available-for-sale Securities, Debt Maturities, Single Maturity Date, Amortized Cost Basis		25,500,000
Available-for-sale Securities, Debt Maturities, Fair Value, Rolling Maturity [Abstract]
Available-for-sale Securities, Debt Maturities, Less Than One Year, Fair Value		0
Available-for-sale Securities, Debt Maturities, One to Five Years, Fair Value		0
Available-for-sale Securities, Debt Maturities, Six to Ten Years, Fair Value		0
Available-for-sale Securities, Debt Maturities, Over Ten Years, Fair Value		25,481,000
Available-for-sale Securities, Debt Maturities, Single Maturity Date, Fair value		$ 25,481,000
Available-for-sale Securities, Debt Maturities, Nominal Yield [Abstract]
Available-for-sale Securities, Debt Maturities, Less than One Year, Nominal Yield		0.00%
Available-for-sale Securities, Debt Maturities, One to Five Years, Nominal Yield		0.00%
Available-for-sale Securities, Debt Maturities, Six to Ten Years, Nominal Yield		0.00%
Available-for-sale Securities, Debt Maturities, Greater Than Ten Years, Nominal Yield		1.59%
Available-for-sale Securities, Debt Maturities, Nominal Yield		1.59%
Available-for-sale Securities, Debt Maturities, Weighted Average Maturity	[1]	14.68
Available-for-sale Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Securities		2		2
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value		$ 19,959,000		$ 0
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value		472,000		4,152,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		20,431,000		4,152,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss		41,000		0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss		28,000		248,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss		69,000		248,000
Residential mortgage-backed securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost		5,429,459,000		5,576,543,000
Available-for-sale Securities, Fair Value		5,402,373,000		5,575,921,000
Available-for-sale Securities, Gross Unrealized Gain		35,605,000		50,377,000
Available-for-sale Securities, Gross Unrealized Loss		(62,300,000)		(50,781,000)
Available-for-Sale Securities, Other Than Temporary Impairments		(391,000)		$ (218,000)
Available-for-sale Securities, Debt Maturities, Amortized Cost, Rolling Maturity [Abstract]
Available-for-sale Securities, Debt Maturities, without Single Maturity Date, Amortized Cost Basis		5,429,459,000
Available-for-sale Securities, Debt Maturities, Fair Value, Rolling Maturity [Abstract]
Available-for-sale Securities, Debt Maturities, without Single Maturity Date, Fair value		$ 5,402,373,000
Available-for-sale Securities, Debt Maturities, Nominal Yield [Abstract]
Available-for-sale Securities, Debt Maturities, Nominal Yield	[4]	2.04%
Available-for-sale Securities, Debt Maturities, Average Expected Life of Mortgage-backed Securities		4 years 73 days
Available-for-sale Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Securities		217		186
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value		$ 2,274,604,000		$ 3,308,229,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value		1,458,587,000		129,716,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		3,733,191,000		3,437,945,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss		18,758,000		47,767,000
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss		43,933,000		3,232,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss		62,691,000		50,999,000
U.S. government agency residential mortgage-backed securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost		5,355,148,000		5,475,351,000
Available-for-sale Securities, Fair Value		5,309,152,000		5,460,386,000
Available-for-sale Securities, Gross Unrealized Gain		16,304,000		35,800,000
Available-for-sale Securities, Gross Unrealized Loss		(62,300,000)		(50,765,000)
Available-for-Sale Securities, Other Than Temporary Impairments		$ 0		$ 0
Available-for-sale Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Securities		209		180
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value		$ 2,268,706,000		$ 3,300,298,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value		1,458,587,000		116,208,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		3,727,293,000		3,416,506,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss		18,367,000		47,593,000
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss		43,933,000		3,172,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss		62,300,000		50,765,000
U.S. government agency residential mortgage-backed securities [Member] | FNMA [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost		3,021,551,000		3,062,525,000
Available-for-sale Securities, Fair Value		2,997,563,000		3,055,676,000
Available-for-sale Securities, Gross Unrealized Gain		11,549,000		25,066,000
Available-for-sale Securities, Gross Unrealized Loss		(35,537,000)		(31,915,000)
Available-for-Sale Securities, Other Than Temporary Impairments		$ 0		$ 0
Available-for-sale Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Securities		113		91
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value		$ 1,203,041,000		$ 1,787,644,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value		824,029,000		72,105,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		2,027,070,000		1,859,749,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss		9,618,000		30,238,000
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss		25,919,000		1,677,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss		35,537,000		31,915,000
U.S. government agency residential mortgage-backed securities [Member] | FHLMC [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost		1,545,971,000		1,534,451,000
Available-for-sale Securities, Fair Value		1,531,009,000		1,531,116,000
Available-for-sale Securities, Gross Unrealized Gain		3,148,000		8,475,000
Available-for-sale Securities, Gross Unrealized Loss		(18,110,000)		(11,810,000)
Available-for-Sale Securities, Other Than Temporary Impairments		$ 0		$ 0
Available-for-sale Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Securities		69		58
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value		$ 863,778,000		$ 964,017,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value		385,816,000		18,307,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		1,249,594,000		982,324,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss		7,297,000		11,210,000
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss		10,813,000		600,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss		18,110,000		11,810,000
U.S. government agency residential mortgage-backed securities [Member] | GNMA [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost		787,626,000		878,375,000
Available-for-sale Securities, Fair Value		780,580,000		873,594,000
Available-for-sale Securities, Gross Unrealized Gain		1,607,000		2,259,000
Available-for-sale Securities, Gross Unrealized Loss		(8,653,000)		(7,040,000)
Available-for-Sale Securities, Other Than Temporary Impairments		$ 0		$ 0
Available-for-sale Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Securities		27		31
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value		$ 201,887,000		$ 548,637,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value		248,742,000		25,796,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		450,629,000		574,433,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss		1,452,000		6,145,000
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss		7,201,000		895,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss		8,653,000		7,040,000
Privately issued residential mortgage-backed securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost		74,311,000		101,192,000
Available-for-sale Securities, Fair Value		93,221,000		115,535,000
Available-for-sale Securities, Gross Unrealized Gain		19,301,000		14,577,000
Available-for-sale Securities, Gross Unrealized Loss		0		(16,000)
Available-for-Sale Securities, Other Than Temporary Impairments		$ (391,000)		$ (218,000)
Available-for-sale Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Securities		8	[5]	6	[6]
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value		$ 5,898,000	[5]	$ 7,931,000	[6]
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value		0	[5]	13,508,000	[6]
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		5,898,000	[5]	21,439,000	[6]
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss		391,000	[5]	174,000	[6]
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss		0	[5]	60,000	[6]
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss		391,000	[5]	234,000	[6]
Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net [Abstract]
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Credit Losses on Debt Securities Held		55,000,000
Perpetual Preferred, Equity Securities and Mutual Funds [Member]
Available-for-sale Securities, Debt Maturities, Amortized Cost, Rolling Maturity [Abstract]
Available-for-sale Securities, Debt Maturities, without Single Maturity Date, Amortized Cost Basis		27,049,000
Available-for-sale Securities, Debt Maturities, Fair Value, Rolling Maturity [Abstract]
Available-for-sale Securities, Debt Maturities, without Single Maturity Date, Fair value		$ 30,683,000
Available-for-sale Securities, Debt Maturities, Nominal Yield [Abstract]
Available-for-sale Securities, Debt Maturities, Nominal Yield		0.00%
Perpetual preferred stock [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost		$ 12,562,000		15,561,000
Available-for-sale Securities, Fair Value		15,767,000		18,474,000
Available-for-sale Securities, Gross Unrealized Gain		3,205,000		2,913,000
Available-for-sale Securities, Gross Unrealized Loss		0		0
Available-for-Sale Securities, Other Than Temporary Impairments		$ 0		$ 0
Available-for-sale Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Securities		0		0
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value		$ 0		$ 0
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value		0		0
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		0		0
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss		0		0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss		0		0
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss		0		0
Equity securities and mutual funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost		14,487,000		17,424,000
Available-for-sale Securities, Fair Value		14,916,000		18,357,000
Available-for-sale Securities, Gross Unrealized Gain		515,000		1,060,000
Available-for-sale Securities, Gross Unrealized Loss		(86,000)		(127,000)
Available-for-Sale Securities, Other Than Temporary Impairments		$ 0		$ 0
Available-for-sale Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Securities		111		104
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value		$ 911,000		$ 2,127,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value		2,203,000		817,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		3,114,000		2,944,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss		7,000		41,000
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss		79,000		86,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss		$ 86,000		$ 127,000
[1]	Expected maturities may differ from contractual maturities, because borrowers may have the right to call or prepay obligations with or without penalty.
[2]	Calculated on a taxable equivalent basis using a 39% effective tax rate.
[3]	Nominal yield on municipal and other tax-exempt securities and other debt securities with contractual maturity dates over ten years are based on variable rates which generally are reset within 35 days.
[4]	The nominal yield on mortgage-backed securities is based upon prepayment assumptions at the purchase date. Actual yields earned may differ significantly based upon actual prepayments. See Quarterly Financial Summary –– Unaudited following for current yields on available for sale securities portfolio.
[5]	Includes securities for which an unrealized loss remains in AOCI after an other-than-temporary credit loss has been recognized in income.
[6]	Includes securities for which an unrealized loss remains in AOCI after an other-than-temporary credit loss has been recognized in income.

Securities Fair Value Option Se

Securities Fair Value Option Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Schedule of Fair Value Option Securities [Line Items]
Fair Value Option Securities, Fair Value	$ 755,054	$ 77,046
U.S. government agency residential mortgage-backed securities [Member]
Schedule of Fair Value Option Securities [Line Items]
Fair Value Option Securities, Fair Value	755,054	77,046
Fair Value Option Securities, Net Unrealized Gain (Loss)	$ (1,877)	$ (1,777)

Securities Restricted Equity Se

Securities Restricted Equity Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Federal Home Loan Bank Stock and Federal Reserve Bank Stock [Abstract]
Federal Reserve Bank Stock	$ 40,746	$ 36,498
Federal Home Loan Bank Stock	279,200	270,541
Other	243	201
Total	$ 320,189	$ 307,240

Derivatives, Fair Value of Deri

Derivatives, Fair Value of Derivatives Contracts (Details) - USD ($) $ in Thousands	Dec. 31, 2017		Dec. 31, 2016
Derivative Assets, Fair Value, Net [Abstract]
Derivative Assets, Fair Value, Net of Cash Collateral	$ 220,502		$ 689,872
Derivative Liabilities, Fair Value, Net [Abstract]
Derivative Liabilities, Fair Value, Net of Cash Collateral	171,963		664,531
Not Designated as Hedging Instrument [Member]
Notional Amount of Derivatives [Abstract]
Derivative Assets, Notional	20,038,522	[1]	22,437,314	[2]
Derivative Liabilities, Notional	20,186,467	[1]	22,178,359	[2]
Derivative Assets, Fair Value, Net [Abstract]
Derivative Assets, Gross Fair Value	301,052		789,791
Derivative Assets, Netting Adjustments	(74,022)		(89,368)
Derivative Assets, Net Fair Value Before Cash Collateral	227,030		700,423
Derivative Assets, Cash Collateral	6,528		10,551
Derivative Assets, Fair Value, Net of Cash Collateral	220,502		689,872
Derivative Liabilities, Fair Value, Net [Abstract]
Derivative Liabilities, Fair Value, Gross Liability	302,405		801,809
Derivative Liabilities, Netting Adjustments	(74,022)		(89,368)
Derivative Liabilities, Net Fair Value Before Cash Collateral	228,383		712,441
Derivative Liabilities, Cash Collateral	56,420		47,910
Derivative Liabilities, Fair Value, Net of Cash Collateral	171,963		664,531
Not Designated as Hedging Instrument [Member] | To-be-announced residential mortgage-backed securities [Member]
Notional Amount of Derivatives [Abstract]
Derivative Assets, Notional	12,347,542	[1]	16,949,152	[2]
Derivative Liabilities, Notional	11,537,742	[1]	16,637,532	[2]
Derivative Assets, Fair Value, Net [Abstract]
Derivative Assets, Gross Fair Value	23,606		180,695
Derivative Assets, Netting Adjustments	(18,096)		(60,555)
Derivative Assets, Net Fair Value Before Cash Collateral	5,510		120,140
Derivative Assets, Cash Collateral	0		0
Derivative Assets, Fair Value, Net of Cash Collateral	5,510		120,140
Derivative Liabilities, Fair Value, Net [Abstract]
Derivative Liabilities, Fair Value, Gross Liability	20,367		176,928
Derivative Liabilities, Netting Adjustments	(18,096)		(60,555)
Derivative Liabilities, Net Fair Value Before Cash Collateral	2,271		116,373
Derivative Liabilities, Cash Collateral	704		0
Derivative Liabilities, Fair Value, Net of Cash Collateral	1,567		116,373
Not Designated as Hedging Instrument [Member] | Interest rate swaps [Member]
Notional Amount of Derivatives [Abstract]
Derivative Assets, Notional	1,478,944	[1]	1,403,408	[2]
Derivative Liabilities, Notional	1,478,944	[1]	1,403,408	[2]
Derivative Assets, Fair Value, Net [Abstract]
Derivative Assets, Gross Fair Value	28,278		34,442
Derivative Assets, Netting Adjustments	0		0
Derivative Assets, Net Fair Value Before Cash Collateral	28,278		34,442
Derivative Assets, Cash Collateral	4,964		4,567
Derivative Assets, Fair Value, Net of Cash Collateral	23,314		29,875
Derivative Liabilities, Fair Value, Net [Abstract]
Derivative Liabilities, Fair Value, Gross Liability	28,298		34,442
Derivative Liabilities, Netting Adjustments	0		0
Derivative Liabilities, Net Fair Value Before Cash Collateral	28,298		34,442
Derivative Liabilities, Cash Collateral	12,896		11,977
Derivative Liabilities, Fair Value, Net of Cash Collateral	15,402		22,465
Not Designated as Hedging Instrument [Member] | Energy contracts [Member]
Notional Amount of Derivatives [Abstract]
Derivative Assets, Notional	1,190,067	[1]	835,566	[2]
Derivative Liabilities, Notional	1,166,924	[1]	820,365	[2]
Derivative Assets, Fair Value, Net [Abstract]
Derivative Assets, Gross Fair Value	103,044		64,140
Derivative Assets, Netting Adjustments	(47,873)		(28,298)
Derivative Assets, Net Fair Value Before Cash Collateral	55,171		35,842
Derivative Assets, Cash Collateral	196		71
Derivative Assets, Fair Value, Net of Cash Collateral	54,975		35,771
Derivative Liabilities, Fair Value, Net [Abstract]
Derivative Liabilities, Fair Value, Gross Liability	101,603		64,306
Derivative Liabilities, Netting Adjustments	(47,873)		(28,298)
Derivative Liabilities, Net Fair Value Before Cash Collateral	53,730		36,008
Derivative Liabilities, Cash Collateral	42,767		31,534
Derivative Liabilities, Fair Value, Net of Cash Collateral	10,963		4,474
Not Designated as Hedging Instrument [Member] | Agricultural contracts [Member]
Notional Amount of Derivatives [Abstract]
Derivative Assets, Notional	53,238	[1]	53,209	[2]
Derivative Liabilities, Notional	48,552	[1]	53,216	[2]
Derivative Assets, Fair Value, Net [Abstract]
Derivative Assets, Gross Fair Value	1,576		1,382
Derivative Assets, Netting Adjustments	(960)		(515)
Derivative Assets, Net Fair Value Before Cash Collateral	616		867
Derivative Assets, Cash Collateral	0		0
Derivative Assets, Fair Value, Net of Cash Collateral	616		867
Derivative Liabilities, Fair Value, Net [Abstract]
Derivative Liabilities, Fair Value, Gross Liability	1,551		1,365
Derivative Liabilities, Netting Adjustments	(960)		(515)
Derivative Liabilities, Net Fair Value Before Cash Collateral	591		850
Derivative Liabilities, Cash Collateral	0		769
Derivative Liabilities, Fair Value, Net of Cash Collateral	591		81
Not Designated as Hedging Instrument [Member] | Foreign exchange contracts [Member]
Notional Amount of Derivatives [Abstract]
Derivative Assets, Notional	132,397	[1]	580,886	[2]
Derivative Liabilities, Notional	126,251	[1]	580,712	[2]
Derivative Assets, Fair Value, Net [Abstract]
Derivative Assets, Gross Fair Value	129,551		494,349
Derivative Assets, Netting Adjustments	0		0
Derivative Assets, Net Fair Value Before Cash Collateral	129,551		494,349
Derivative Assets, Cash Collateral	448		5,183
Derivative Assets, Fair Value, Net of Cash Collateral	129,103		489,166
Derivative Liabilities, Fair Value, Net [Abstract]
Derivative Liabilities, Fair Value, Gross Liability	123,321		494,695
Derivative Liabilities, Netting Adjustments	0		0
Derivative Liabilities, Net Fair Value Before Cash Collateral	123,321		494,695
Derivative Liabilities, Cash Collateral	53		3,630
Derivative Liabilities, Fair Value, Net of Cash Collateral	123,268		491,065
Not Designated as Hedging Instrument [Member] | Equity option contracts [Member]
Notional Amount of Derivatives [Abstract]
Derivative Assets, Notional	99,633	[1]	100,924	[2]
Derivative Liabilities, Notional	99,633	[1]	100,924	[2]
Derivative Assets, Fair Value, Net [Abstract]
Derivative Assets, Gross Fair Value	5,503		4,357
Derivative Assets, Netting Adjustments	0		0
Derivative Assets, Net Fair Value Before Cash Collateral	5,503		4,357
Derivative Assets, Cash Collateral	920		730
Derivative Assets, Fair Value, Net of Cash Collateral	4,583		3,627
Derivative Liabilities, Fair Value, Net [Abstract]
Derivative Liabilities, Fair Value, Gross Liability	5,503		4,357
Derivative Liabilities, Netting Adjustments	0		0
Derivative Liabilities, Net Fair Value Before Cash Collateral	5,503		4,357
Derivative Liabilities, Cash Collateral	0		0
Derivative Liabilities, Fair Value, Net of Cash Collateral	5,503		4,357
Not Designated as Hedging Instrument [Member] | Total customer risk management programs [Member]
Notional Amount of Derivatives [Abstract]
Derivative Assets, Notional	15,301,821	[1]	19,923,145	[2]
Derivative Liabilities, Notional	14,458,046	[1]	19,596,157	[2]
Derivative Assets, Fair Value, Net [Abstract]
Derivative Assets, Gross Fair Value	291,558		779,365
Derivative Assets, Netting Adjustments	(66,929)		(89,368)
Derivative Assets, Net Fair Value Before Cash Collateral	224,629		689,997
Derivative Assets, Cash Collateral	6,528		10,551
Derivative Assets, Fair Value, Net of Cash Collateral	218,101		679,446
Derivative Liabilities, Fair Value, Net [Abstract]
Derivative Liabilities, Fair Value, Gross Liability	280,643		776,093
Derivative Liabilities, Netting Adjustments	(66,929)		(89,368)
Derivative Liabilities, Net Fair Value Before Cash Collateral	213,714		686,725
Derivative Liabilities, Cash Collateral	56,420		47,910
Derivative Liabilities, Fair Value, Net of Cash Collateral	157,294		638,815
Not Designated as Hedging Instrument [Member] | Internal risk management programs [Member]
Notional Amount of Derivatives [Abstract]
Derivative Assets, Notional	4,736,701	[1]	2,514,169	[2]
Derivative Liabilities, Notional	5,728,421	[1]	2,582,202	[2]
Derivative Assets, Fair Value, Net [Abstract]
Derivative Assets, Gross Fair Value	9,494		10,426
Derivative Assets, Netting Adjustments	(7,093)		0
Derivative Assets, Net Fair Value Before Cash Collateral	2,401		10,426
Derivative Assets, Cash Collateral	0		0
Derivative Assets, Fair Value, Net of Cash Collateral	2,401		10,426
Derivative Liabilities, Fair Value, Net [Abstract]
Derivative Liabilities, Fair Value, Gross Liability	21,762		25,716
Derivative Liabilities, Netting Adjustments	(7,093)		0
Derivative Liabilities, Net Fair Value Before Cash Collateral	14,669		25,716
Derivative Liabilities, Cash Collateral	0		0
Derivative Liabilities, Fair Value, Net of Cash Collateral	$ 14,669		$ 25,716
[1]	Notional amounts for commodity contracts are converted into dollar-equivalent amounts based on dollar prices at the inception of the contract.
[2]	Notional amounts for commodity contracts are converted into dollar-equivalent amounts based on dollar prices at the inception of the contract.

Loans and Allowances for Cred61

Loans and Allowances for Credit Losses, Loans by Portfolio Segment (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016
Loans receivables disclosure [Abstract]
Loans receivables with fixed rate of interest		$ 4,529,296	$ 4,753,600
Loans receivables with variable rate of interest		12,436,254	12,005,076
Loan receivable non-accrual		187,874	230,984
Total		17,153,424	16,989,660
Accruing loans past due (90 days)	[1]	633	5
Foregone interest on nonaccrual loans		16,496	15,990
Credit Commitments [Abstract]
Outstanding commitments to extend credit		10,000,000
Outstanding standby letters of credit		648,000
Outstanding commercial letters of credit		3,200
Geographic Concentration Risk [Member] | Texas [Member]
Loans receivables disclosure [Abstract]
Total		$ 5,800,000	$ 5,400,000
Loans receivable, other information [Abstract]
Percentage of loan portfolio attributed to Texas		34.00%	32.00%
Geographic Concentration Risk [Member] | Oklahoma [Member]
Loans receivables disclosure [Abstract]
Total		$ 3,300,000	$ 3,500,000
Loans receivable, other information [Abstract]
Percentage of loan portfolio attributed to Oklahoma		19.00%	21.00%
Commercial [Member]
Loans receivables disclosure [Abstract]
Loans receivables with fixed rate of interest		$ 2,217,432	$ 2,327,085
Loans receivables with variable rate of interest		8,379,240	7,884,786
Loan receivable non-accrual		137,303	178,953
Total		10,733,975	10,390,824
Commercial [Member] | Geographic Concentration Risk [Member] | Texas [Member]
Loans receivables disclosure [Abstract]
Total		$ 3,600,000	$ 3,300,000
Loans receivable, other information [Abstract]
Percentage of loan portfolio attributed to Texas		34.00%	32.00%
Commercial [Member] | Geographic Concentration Risk [Member] | Oklahoma [Member]
Loans receivables disclosure [Abstract]
Total		$ 2,000,000	$ 2,100,000
Loans receivable, other information [Abstract]
Percentage of loan portfolio attributed to Oklahoma		18.00%	21.00%
Commercial [Member] | Services [Member]
Loans receivables disclosure [Abstract]
Total		$ 2,986,949	$ 3,108,990
Commercial [Member] | Services [Member] | Credit Concentration Risk [Member]
Loans receivables disclosure [Abstract]
Total		$ 3,000,000	$ 3,100,000
Loans receivable, other information [Abstract]
Percentage of loan class to total loans		17.00%	18.00%
Amount of loans with individual balances less than $10 million		$ 1,500,000	$ 1,400,000
Maximum loan amount for certain individual loans in category		10,000	10,000
Commercial [Member] | Energy [Member]
Loans receivables disclosure [Abstract]
Total		2,930,156	2,497,868
Commercial [Member] | Energy [Member] | Credit Concentration Risk [Member]
Loans receivables disclosure [Abstract]
Total		$ 2,900,000	$ 2,500,000
Loans receivable, other information [Abstract]
Percentage of loan class to total loans		17.00%	15.00%
Commercial [Member] | Energy Producers [Member] | Credit Concentration Risk [Member]
Loans receivables disclosure [Abstract]
Total		$ 2,500,000	$ 2,000,000
Loans receivable, other information [Abstract]
Percentage of committed energy production loans secured by oil		57.00%	57.00%
Percentage of committed energy production loans secured by natural gas		43.00%	43.00%
Commercial [Member] | Healthcare [Member]
Loans receivables disclosure [Abstract]
Total		$ 2,314,753	$ 2,201,916
Commercial [Member] | Healthcare [Member] | Credit Concentration Risk [Member]
Loans receivables disclosure [Abstract]
Total		$ 2,300,000	$ 2,200,000
Loans receivable, other information [Abstract]
Percentage of loan class to total loans		13.00%	13.00%
Commercial Real Estate [Member]
Loans receivables disclosure [Abstract]
Loans receivables with fixed rate of interest		$ 548,692	$ 624,187
Loans receivables with variable rate of interest		2,928,440	3,179,338
Loan receivable non-accrual		2,855	5,521
Total		$ 3,479,987	$ 3,809,046
Commercial Real Estate [Member] | Geographic Concentration Risk [Member] | Texas [Member]
Loans receivable, other information [Abstract]
Percentage of loan portfolio secured by property in Texas (in hundredths)		35.00%	30.00%
Commercial Real Estate [Member] | Geographic Concentration Risk [Member] | Oklahoma [Member]
Loans receivable, other information [Abstract]
Percentage of loan portfolio secured by property in Oklahoma (in hundredths)		12.00%	11.00%
Residential Mortgage [Member]
Loans receivables disclosure [Abstract]
Loans receivables with fixed rate of interest		$ 1,608,655	$ 1,647,357
Loans receivables with variable rate of interest		317,584	256,255
Loan receivable non-accrual		47,447	46,220
Total		$ 1,973,686	$ 1,949,832
Residential Mortgage [Member] | Geographic Concentration Risk [Member] | Texas [Member]
Loans receivable, other information [Abstract]
Percentage of loan portfolio secured by property in Texas (in hundredths)		30.00%	29.00%
Residential Mortgage [Member] | Geographic Concentration Risk [Member] | Oklahoma [Member]
Loans receivable, other information [Abstract]
Percentage of loan portfolio secured by property in Oklahoma (in hundredths)		31.00%	33.00%
Residential Mortgage [Member] | Geographic Concentration Risk [Member] | New Mexico [Memnber]
Loans receivable, other information [Abstract]
Percentage of loan portfolio secured by property in New Mexico (in hundredths)			10.00%
Residential Mortgage [Member] | Geographic Concentration Risk [Member] | Colorado [Member]
Loans receivable, other information [Abstract]
Percentage of loan portfolio secured by property in Colorado (in hundredths)		11.00%	10.00%
Residential Mortgage [Member] | Permanent mortgage [Member]
Loans receivables disclosure [Abstract]
Total		$ 1,043,435	$ 1,006,820
Loans receivable, other information [Abstract]
Minimum FICO required for jumbo loan approval		720
Maximum debt-to-income ratio on jumbo loans (in hundredths)		38.00%
Minimum loan-to-value ratio on jumbo loans (in hundredths)		60.00%
Maximum loan-to-value ratio on jumbo loans (in hundredths)		100.00%
Minimum period for fixed rate on variable rate jumbo loans (in years)		3 years
Maximum period for fixed rate on variable rate jumbo loans (in years)		10 years
Residential Mortgage [Member] | Permanent mortgages guaranteed by U.S. government agencies [Member]
Loans receivables disclosure [Abstract]
Total		$ 197,506	199,387
Residential Mortgage [Member] | Home equity [Member]
Loans receivables disclosure [Abstract]
Total		732,745	$ 743,625
Loans receivable, other information [Abstract]
Maximum loan amount for certain individual loans in category		$ 400
Percentage of home equity portfolio comprised of first lien loans		64.00%	65.00%
Percentage of home equity portfolio comprised of junior lien loans		36.00%	35.00%
Percentage of junior lien home equity loans that are amortizing term loans		46.00%	52.00%
Percentage of junior lien home equity loans that are revolving lines of credit		54.00%	48.00%
Home equity loans, description		Home equity loans generally require a minimum FICO score of 700 and a maximum DTI of 40%.
Home equity loans, revolving period		5 years
Home equity loans, amortization period following revolving period		15 years
Home equity loans, discretionary additional revolving period		5 years
Personal [Member]
Loans receivables disclosure [Abstract]
Loans receivables with fixed rate of interest		$ 154,517	$ 154,971
Loans receivables with variable rate of interest		810,990	684,697
Loan receivable non-accrual		269	290
Total		$ 965,776	$ 839,958
[1]	Excludes residential mortgage loans guaranteed by agencies of the U.S. government

Derivatives, Derivatives Instru

Derivatives, Derivatives Instruments Gain (Loss) in Income Statement (Details) - Not Designated as Hedging Instrument [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Trading Activity, Gains and Losses, Net [Line Items]
Brokerage and Trading Revenue	$ 48,761	$ 42,603	$ 40,714
Gain (Loss) on Derivatives, Net	779	(15,685)	430
To-be-announced residential mortgage-backed securities [Member]
Trading Activity, Gains and Losses, Net [Line Items]
Brokerage and Trading Revenue	34,532	38,523	33,877
Gain (Loss) on Derivatives, Net	0	0	0
Interest rate swaps [Member]
Trading Activity, Gains and Losses, Net [Line Items]
Brokerage and Trading Revenue	2,647	2,589	2,066
Gain (Loss) on Derivatives, Net	0	0	0
Energy contracts [Member]
Trading Activity, Gains and Losses, Net [Line Items]
Brokerage and Trading Revenue	5,536	5,027	4,060
Gain (Loss) on Derivatives, Net	0	0	0
Agricultural contracts [Member]
Trading Activity, Gains and Losses, Net [Line Items]
Brokerage and Trading Revenue	79	111	123
Gain (Loss) on Derivatives, Net	0	0	0
Foreign exchange contracts [Member]
Trading Activity, Gains and Losses, Net [Line Items]
Brokerage and Trading Revenue	1,352	945	797
Gain (Loss) on Derivatives, Net	0	0	0
Equity option contracts [Member]
Trading Activity, Gains and Losses, Net [Line Items]
Brokerage and Trading Revenue	0	0	0
Gain (Loss) on Derivatives, Net	0	0	0
Total customer risk management programs [Member]
Trading Activity, Gains and Losses, Net [Line Items]
Brokerage and Trading Revenue	44,146	47,195	40,923
Gain (Loss) on Derivatives, Net	0	0	0
Internal risk management programs [Member]
Trading Activity, Gains and Losses, Net [Line Items]
Brokerage and Trading Revenue	4,615	(4,592)	(209)
Gain (Loss) on Derivatives, Net	$ 779	$ (15,685)	$ 430

Loans and Allowances for Cred63

Loans and Allowances for Credit Losses, Activity in Allowance for Credit Losses (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2017	Dec. 31, 2016
Allowance for loan losses [Roll Forward]
Beginning balance	$ 246,159	$ 225,524	$ 189,056
Provision for loan losses	510	55,467	33,519
Loans charged off	(25,599)	(42,588)	(15,171)
Recoveries	9,612	7,756	18,120
Ending balance	230,682	246,159	225,524
Accrual for off-balance sheet credit losses [Roll Forward]
Beginning balance	11,244	1,711	1,230
Provision for off-balance sheet credit risk	(7,510)	9,533	481
Ending balance	3,734	11,244	1,711
Total provision for credit losses	(7,000)	65,000	34,000
Recorded investment [Abstract]
Collectively measured for impairment, recorded investment				$ 16,965,550	$ 16,758,676
Individually measured for impairment, recorded investment				187,874	230,984
Total				17,153,424	16,989,660
Related allowance [Abstract]
Collectively measured for impairment, related allowance				199,634	217,116
Individually measured for impairment, related allowance				8,831	843
Total measured for impairment, related allowance	246,159	225,524	189,056	230,682	246,159
Commercial [Member]
Allowance for loan losses [Roll Forward]
Beginning balance	140,213	130,334	90,875
Provision for loan losses	(595)	43,980	43,464
Loans charged off	(19,810)	(35,828)	(6,734)
Recoveries	4,461	1,727	2,729
Ending balance	124,269	140,213	130,334
Accrual for off-balance sheet credit losses [Roll Forward]
Beginning balance	11,063	1,506	475
Provision for off-balance sheet credit risk	(7,419)	9,557	1,031
Ending balance	3,644	11,063	1,506
Total provision for credit losses	(8,014)	53,537	44,495
Recorded investment [Abstract]
Collectively measured for impairment, recorded investment				10,596,672	10,211,871
Individually measured for impairment, recorded investment				137,303	178,953
Total				10,733,975	10,390,824
Related allowance [Abstract]
Collectively measured for impairment, related allowance				115,438	139,416
Individually measured for impairment, related allowance				8,831	797
Total measured for impairment, related allowance	140,213	130,334	90,875	124,269	140,213
Commercial Real Estate [Member]
Allowance for loan losses [Roll Forward]
Beginning balance	50,749	41,391	42,445
Provision for loan losses	4,008	8,075	(11,189)
Loans charged off	(76)	0	(944)
Recoveries	1,940	1,283	11,079
Ending balance	56,621	50,749	41,391
Accrual for off-balance sheet credit losses [Roll Forward]
Beginning balance	123	153	707
Provision for off-balance sheet credit risk	(78)	(30)	(554)
Ending balance	45	123	153
Total provision for credit losses	3,930	8,045	(11,743)
Recorded investment [Abstract]
Collectively measured for impairment, recorded investment				3,477,132	3,803,525
Individually measured for impairment, recorded investment				2,855	5,521
Total				3,479,987	3,809,046
Related allowance [Abstract]
Collectively measured for impairment, related allowance				56,621	50,749
Individually measured for impairment, related allowance				0	0
Total measured for impairment, related allowance	50,749	41,391	42,445	56,621	50,749
Residential Mortgage [Member]
Allowance for loan losses [Roll Forward]
Beginning balance	18,224	19,509	23,458
Provision for loan losses	116	(1,972)	(3,004)
Loans charged off	(649)	(1,312)	(2,205)
Recoveries	760	1,999	1,260
Ending balance	18,451	18,224	19,509
Accrual for off-balance sheet credit losses [Roll Forward]
Beginning balance	50	30	28
Provision for off-balance sheet credit risk	(7)	20	2
Ending balance	43	50	30
Total provision for credit losses	109	(1,952)	(3,002)
Recorded investment [Abstract]
Collectively measured for impairment, recorded investment				1,926,239	1,903,612
Individually measured for impairment, recorded investment				47,447	46,220
Total				1,973,686	1,949,832
Related allowance [Abstract]
Collectively measured for impairment, related allowance				18,451	18,178
Individually measured for impairment, related allowance				0	46
Total measured for impairment, related allowance	18,224	19,509	23,458	18,451	18,224
Personal [Member]
Allowance for loan losses [Roll Forward]
Beginning balance	8,773	4,164	4,233
Provision for loan losses	2,964	7,310	2,167
Loans charged off	(5,064)	(5,448)	(5,288)
Recoveries	2,451	2,747	3,052
Ending balance	9,124	8,773	4,164
Accrual for off-balance sheet credit losses [Roll Forward]
Beginning balance	8	22	20
Provision for off-balance sheet credit risk	(6)	(14)	2
Ending balance	2	8	22
Total provision for credit losses	2,958	7,296	2,169
Recorded investment [Abstract]
Collectively measured for impairment, recorded investment				965,507	839,668
Individually measured for impairment, recorded investment				269	290
Total				965,776	839,958
Related allowance [Abstract]
Collectively measured for impairment, related allowance				9,124	8,773
Individually measured for impairment, related allowance				0	0
Total measured for impairment, related allowance	8,773	4,164	4,233	9,124	8,773
Specific Allowance [Member]
Allowance for loan losses [Roll Forward]
Beginning balance	217,959
Ending balance	208,465	217,959
Recorded investment [Abstract]
Collectively measured for impairment, recorded investment				16,965,550	16,758,676
Individually measured for impairment, recorded investment				187,874	230,984
Total				17,153,424	16,989,660
Related allowance [Abstract]
Collectively measured for impairment, related allowance				199,634	217,116
Individually measured for impairment, related allowance				8,831	843
Total measured for impairment, related allowance	217,959	217,959		208,465	217,959
Nonspecific Allowance [Member]
Allowance for loan losses [Roll Forward]
Beginning balance	28,200	30,126	28,045
Provision for loan losses	(5,983)	(1,926)	2,081
Loans charged off	0	0	0
Recoveries	0	0	0
Ending balance	22,217	28,200	30,126
Accrual for off-balance sheet credit losses [Roll Forward]
Beginning balance	0	0	0
Provision for off-balance sheet credit risk	0	0	0
Ending balance	0	0	0
Total provision for credit losses	(5,983)	(1,926)	2,081
Recorded investment [Abstract]
Collectively measured for impairment, recorded investment				0	0
Individually measured for impairment, recorded investment				0	0
Total				0	0
Related allowance [Abstract]
Collectively measured for impairment, related allowance				0	0
Individually measured for impairment, related allowance				0	0
Total measured for impairment, related allowance	$ 28,200	$ 30,126	$ 28,045	$ 22,217	$ 28,200

Loans and Allowances for Cred64

Loans and Allowances for Credit Losses, Credit Quality Indicators (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Recorded Investment [Abstract]
Internally Risk Graded, Recorded Investment	$ 15,297,889	$ 15,158,076
Non-Graded, Recorded Investment	1,855,535	1,831,584
Total	17,153,424	16,989,660
Related Allowance [Abstract]
Internally Risk Graded, Related Allowance	189,412	197,970
Non-Graded, Related Allowance	19,053	19,989
Total, Related Allowance	230,682	246,159	$ 225,524	$ 189,056
Commercial [Member]
Recorded Investment [Abstract]
Internally Risk Graded, Recorded Investment	10,706,035	10,360,725
Non-Graded, Recorded Investment	27,940	30,099
Total	10,733,975	10,390,824
Related Allowance [Abstract]
Internally Risk Graded, Related Allowance	123,383	139,293
Non-Graded, Related Allowance	886	920
Total, Related Allowance	124,269	140,213	130,334	90,875
Commercial [Member] | Energy [Member]
Recorded Investment [Abstract]
Total	2,930,156	2,497,868
Commercial [Member] | Services [Member]
Recorded Investment [Abstract]
Total	2,986,949	3,108,990
Commercial [Member] | Wholesale/retail [Member]
Recorded Investment [Abstract]
Total	1,471,256	1,576,818
Commercial [Member] | Manufacturing [Member]
Recorded Investment [Abstract]
Total	496,774	514,975
Commercial [Member] | Healthcare [Member]
Recorded Investment [Abstract]
Total	2,314,753	2,201,916
Commercial [Member] | Other commercial and industrial [Member]
Recorded Investment [Abstract]
Total	534,087	490,257
Commercial Real Estate [Member]
Recorded Investment [Abstract]
Internally Risk Graded, Recorded Investment	3,479,987	3,809,046
Non-Graded, Recorded Investment	0	0
Total	3,479,987	3,809,046
Related Allowance [Abstract]
Internally Risk Graded, Related Allowance	56,621	50,749
Non-Graded, Related Allowance	0	0
Total, Related Allowance	56,621	50,749	41,391	42,445
Commercial Real Estate [Member] | Residential construction and land development [Member]
Recorded Investment [Abstract]
Total	117,245	135,533
Commercial Real Estate [Member] | Retail [Member]
Recorded Investment [Abstract]
Total	691,532	761,888
Commercial Real Estate [Member] | Office [Member]
Recorded Investment [Abstract]
Total	831,770	798,888
Commercial Real Estate [Member] | Multifamily [Member]
Recorded Investment [Abstract]
Total	980,017	903,272
Commercial Real Estate [Member] | Industrial [Member]
Recorded Investment [Abstract]
Total	573,014	871,749
Commercial Real Estate [Member] | Other commercial real estate [Member]
Recorded Investment [Abstract]
Total	286,409	337,716
Residential Mortgage [Member]
Recorded Investment [Abstract]
Internally Risk Graded, Recorded Investment	234,477	243,703
Non-Graded, Recorded Investment	1,739,209	1,706,129
Total	1,973,686	1,949,832
Related Allowance [Abstract]
Internally Risk Graded, Related Allowance	2,947	2,893
Non-Graded, Related Allowance	15,504	15,331
Total, Related Allowance	18,451	18,224	19,509	23,458
Residential Mortgage [Member] | Permanent mortgage [Member]
Recorded Investment [Abstract]
Total	1,043,435	1,006,820
Residential Mortgage [Member] | Permanent mortgages guaranteed by U.S. government agencies [Member]
Recorded Investment [Abstract]
Total	197,506	199,387
Residential Mortgage [Member] | Home equity [Member]
Recorded Investment [Abstract]
Total	732,745	743,625
Personal [Member]
Recorded Investment [Abstract]
Internally Risk Graded, Recorded Investment	877,390	744,602
Non-Graded, Recorded Investment	88,386	95,356
Total	965,776	839,958
Related Allowance [Abstract]
Internally Risk Graded, Related Allowance	6,461	5,035
Non-Graded, Related Allowance	2,663	3,738
Total, Related Allowance	9,124	8,773	4,164	4,233
Specific Allowance [Member]
Recorded Investment [Abstract]
Internally Risk Graded, Recorded Investment	15,297,889	15,158,076
Non-Graded, Recorded Investment	1,855,535	1,831,584
Total	17,153,424	16,989,660
Related Allowance [Abstract]
Internally Risk Graded, Related Allowance	189,412	197,970
Non-Graded, Related Allowance	19,053	19,989
Total, Related Allowance	208,465	217,959
Nonspecific Allowance [Member]
Recorded Investment [Abstract]
Internally Risk Graded, Recorded Investment	0	0
Non-Graded, Recorded Investment	0	0
Total	0	0
Related Allowance [Abstract]
Internally Risk Graded, Related Allowance	0	0
Non-Graded, Related Allowance	0	0
Total, Related Allowance	22,217	28,200	$ 30,126	$ 28,045
Performing [Member]
Recorded Investment [Abstract]
Non-Graded, Recorded Investment	1,808,995	1,786,530
Performing [Member] | Commercial [Member]
Recorded Investment [Abstract]
Non-Graded, Recorded Investment	27,870	30,041
Performing [Member] | Commercial [Member] | Energy [Member]
Recorded Investment [Abstract]
Non-Graded, Recorded Investment	0	0
Performing [Member] | Commercial [Member] | Services [Member]
Recorded Investment [Abstract]
Non-Graded, Recorded Investment	0	0
Performing [Member] | Commercial [Member] | Wholesale/retail [Member]
Recorded Investment [Abstract]
Non-Graded, Recorded Investment	0	0
Performing [Member] | Commercial [Member] | Manufacturing [Member]
Recorded Investment [Abstract]
Non-Graded, Recorded Investment	0	0
Performing [Member] | Commercial [Member] | Healthcare [Member]
Recorded Investment [Abstract]
Non-Graded, Recorded Investment	0	0
Performing [Member] | Commercial [Member] | Other commercial and industrial [Member]
Recorded Investment [Abstract]
Non-Graded, Recorded Investment	27,870	30,041
Performing [Member] | Commercial Real Estate [Member]
Recorded Investment [Abstract]
Non-Graded, Recorded Investment	0	0
Performing [Member] | Commercial Real Estate [Member] | Residential construction and land development [Member]
Recorded Investment [Abstract]
Non-Graded, Recorded Investment	0	0
Performing [Member] | Commercial Real Estate [Member] | Retail [Member]
Recorded Investment [Abstract]
Non-Graded, Recorded Investment	0	0
Performing [Member] | Commercial Real Estate [Member] | Office [Member]
Recorded Investment [Abstract]
Non-Graded, Recorded Investment	0	0
Performing [Member] | Commercial Real Estate [Member] | Multifamily [Member]
Recorded Investment [Abstract]
Non-Graded, Recorded Investment	0	0
Performing [Member] | Commercial Real Estate [Member] | Industrial [Member]
Recorded Investment [Abstract]
Non-Graded, Recorded Investment	0	0
Performing [Member] | Commercial Real Estate [Member] | Other commercial real estate [Member]
Recorded Investment [Abstract]
Non-Graded, Recorded Investment	0	0
Performing [Member] | Residential Mortgage [Member]
Recorded Investment [Abstract]
Non-Graded, Recorded Investment	1,692,925	1,661,326
Performing [Member] | Residential Mortgage [Member] | Permanent mortgage [Member]
Recorded Investment [Abstract]
Non-Graded, Recorded Investment	784,928	741,679
Performing [Member] | Residential Mortgage [Member] | Permanent mortgages guaranteed by U.S. government agencies [Member]
Recorded Investment [Abstract]
Non-Graded, Recorded Investment	188,000	188,000
Performing [Member] | Residential Mortgage [Member] | Home equity [Member]
Recorded Investment [Abstract]
Non-Graded, Recorded Investment	719,670	732,106
Performing [Member] | Personal [Member]
Recorded Investment [Abstract]
Non-Graded, Recorded Investment	88,200	95,163
Performing [Member] | Pass [Member]
Recorded Investment [Abstract]
Internally Risk Graded, Recorded Investment	14,797,279	14,343,507
Performing [Member] | Pass [Member] | Commercial [Member]
Recorded Investment [Abstract]
Internally Risk Graded, Recorded Investment	10,226,089	9,567,816
Performing [Member] | Pass [Member] | Commercial [Member] | Energy [Member]
Recorded Investment [Abstract]
Internally Risk Graded, Recorded Investment	2,632,986	1,937,790
Performing [Member] | Pass [Member] | Commercial [Member] | Services [Member]
Recorded Investment [Abstract]
Internally Risk Graded, Recorded Investment	2,943,869	3,052,002
Performing [Member] | Pass [Member] | Commercial [Member] | Wholesale/retail [Member]
Recorded Investment [Abstract]
Internally Risk Graded, Recorded Investment	1,443,917	1,535,463
Performing [Member] | Pass [Member] | Commercial [Member] | Manufacturing [Member]
Recorded Investment [Abstract]
Internally Risk Graded, Recorded Investment	472,869	468,314
Performing [Member] | Pass [Member] | Commercial [Member] | Healthcare [Member]
Recorded Investment [Abstract]
Internally Risk Graded, Recorded Investment	2,253,497	2,140,458
Performing [Member] | Pass [Member] | Commercial [Member] | Other commercial and industrial [Member]
Recorded Investment [Abstract]
Internally Risk Graded, Recorded Investment	478,951	433,789
Performing [Member] | Pass [Member] | Commercial Real Estate [Member]
Recorded Investment [Abstract]
Internally Risk Graded, Recorded Investment	3,463,002	3,793,471
Performing [Member] | Pass [Member] | Commercial Real Estate [Member] | Residential construction and land development [Member]
Recorded Investment [Abstract]
Internally Risk Graded, Recorded Investment	113,190	131,630
Performing [Member] | Pass [Member] | Commercial Real Estate [Member] | Retail [Member]
Recorded Investment [Abstract]
Internally Risk Graded, Recorded Investment	686,915	756,418
Performing [Member] | Pass [Member] | Commercial Real Estate [Member] | Office [Member]
Recorded Investment [Abstract]
Internally Risk Graded, Recorded Investment	824,408	798,462
Performing [Member] | Pass [Member] | Commercial Real Estate [Member] | Multifamily [Member]
Recorded Investment [Abstract]
Internally Risk Graded, Recorded Investment	979,969	898,800
Performing [Member] | Pass [Member] | Commercial Real Estate [Member] | Industrial [Member]
Recorded Investment [Abstract]
Internally Risk Graded, Recorded Investment	573,014	871,673
Performing [Member] | Pass [Member] | Commercial Real Estate [Member] | Other commercial real estate [Member]
Recorded Investment [Abstract]
Internally Risk Graded, Recorded Investment	285,506	336,488
Performing [Member] | Pass [Member] | Residential Mortgage [Member]
Recorded Investment [Abstract]
Internally Risk Graded, Recorded Investment	232,492	238,769
Performing [Member] | Pass [Member] | Residential Mortgage [Member] | Permanent mortgage [Member]
Recorded Investment [Abstract]
Internally Risk Graded, Recorded Investment	232,492	238,769
Performing [Member] | Pass [Member] | Residential Mortgage [Member] | Permanent mortgages guaranteed by U.S. government agencies [Member]
Recorded Investment [Abstract]
Internally Risk Graded, Recorded Investment	0	0
Performing [Member] | Pass [Member] | Residential Mortgage [Member] | Home equity [Member]
Recorded Investment [Abstract]
Internally Risk Graded, Recorded Investment	0	0
Performing [Member] | Pass [Member] | Personal [Member]
Recorded Investment [Abstract]
Internally Risk Graded, Recorded Investment	875,696	743,451
Performing [Member] | Other Loans Especially Mentioned [Member]
Recorded Investment [Abstract]
Internally Risk Graded, Recorded Investment	118,175	229,673
Performing [Member] | Other Loans Especially Mentioned [Member] | Commercial [Member]
Recorded Investment [Abstract]
Internally Risk Graded, Recorded Investment	103,324	223,742
Performing [Member] | Other Loans Especially Mentioned [Member] | Commercial [Member] | Energy [Member]
Recorded Investment [Abstract]
Internally Risk Graded, Recorded Investment	60,288	119,583
Performing [Member] | Other Loans Especially Mentioned [Member] | Commercial [Member] | Services [Member]
Recorded Investment [Abstract]
Internally Risk Graded, Recorded Investment	13,927	10,960
Performing [Member] | Other Loans Especially Mentioned [Member] | Commercial [Member] | Wholesale/retail [Member]
Recorded Investment [Abstract]
Internally Risk Graded, Recorded Investment	19,263	16,886
Performing [Member] | Other Loans Especially Mentioned [Member] | Commercial [Member] | Manufacturing [Member]
Recorded Investment [Abstract]
Internally Risk Graded, Recorded Investment	6,653	26,532
Performing [Member] | Other Loans Especially Mentioned [Member] | Commercial [Member] | Healthcare [Member]
Recorded Investment [Abstract]
Internally Risk Graded, Recorded Investment	3,186	44,472
Performing [Member] | Other Loans Especially Mentioned [Member] | Commercial [Member] | Other commercial and industrial [Member]
Recorded Investment [Abstract]
Internally Risk Graded, Recorded Investment	7	5,309
Performing [Member] | Other Loans Especially Mentioned [Member] | Commercial Real Estate [Member]
Recorded Investment [Abstract]
Internally Risk Graded, Recorded Investment	13,303	4,745
Performing [Member] | Other Loans Especially Mentioned [Member] | Commercial Real Estate [Member] | Residential construction and land development [Member]
Recorded Investment [Abstract]
Internally Risk Graded, Recorded Investment	1,828	0
Performing [Member] | Other Loans Especially Mentioned [Member] | Commercial Real Estate [Member] | Retail [Member]
Recorded Investment [Abstract]
Internally Risk Graded, Recorded Investment	4,243	4,745
Performing [Member] | Other Loans Especially Mentioned [Member] | Commercial Real Estate [Member] | Office [Member]
Recorded Investment [Abstract]
Internally Risk Graded, Recorded Investment	7,087	0
Performing [Member] | Other Loans Especially Mentioned [Member] | Commercial Real Estate [Member] | Multifamily [Member]
Recorded Investment [Abstract]
Internally Risk Graded, Recorded Investment	0	0
Performing [Member] | Other Loans Especially Mentioned [Member] | Commercial Real Estate [Member] | Industrial [Member]
Recorded Investment [Abstract]
Internally Risk Graded, Recorded Investment	0	0
Performing [Member] | Other Loans Especially Mentioned [Member] | Commercial Real Estate [Member] | Other commercial real estate [Member]
Recorded Investment [Abstract]
Internally Risk Graded, Recorded Investment	145	0
Performing [Member] | Other Loans Especially Mentioned [Member] | Residential Mortgage [Member]
Recorded Investment [Abstract]
Internally Risk Graded, Recorded Investment	0	1,186
Performing [Member] | Other Loans Especially Mentioned [Member] | Residential Mortgage [Member] | Permanent mortgage [Member]
Recorded Investment [Abstract]
Internally Risk Graded, Recorded Investment	0	1,186
Performing [Member] | Other Loans Especially Mentioned [Member] | Residential Mortgage [Member] | Permanent mortgages guaranteed by U.S. government agencies [Member]
Recorded Investment [Abstract]
Internally Risk Graded, Recorded Investment	0	0
Performing [Member] | Other Loans Especially Mentioned [Member] | Residential Mortgage [Member] | Home equity [Member]
Recorded Investment [Abstract]
Internally Risk Graded, Recorded Investment	0	0
Performing [Member] | Other Loans Especially Mentioned [Member] | Personal [Member]
Recorded Investment [Abstract]
Internally Risk Graded, Recorded Investment	1,548	0
Performing [Member] | Substandard [Member]
Recorded Investment [Abstract]
Internally Risk Graded, Recorded Investment	241,101	398,966
Performing [Member] | Substandard [Member] | Commercial [Member]
Recorded Investment [Abstract]
Internally Risk Graded, Recorded Investment	239,389	390,272
Performing [Member] | Substandard [Member] | Commercial [Member] | Energy [Member]
Recorded Investment [Abstract]
Internally Risk Graded, Recorded Investment	144,598	307,996
Performing [Member] | Substandard [Member] | Commercial [Member] | Services [Member]
Recorded Investment [Abstract]
Internally Risk Graded, Recorded Investment	26,533	37,855
Performing [Member] | Substandard [Member] | Commercial [Member] | Wholesale/retail [Member]
Recorded Investment [Abstract]
Internally Risk Graded, Recorded Investment	5,502	13,062
Performing [Member] | Substandard [Member] | Commercial [Member] | Manufacturing [Member]
Recorded Investment [Abstract]
Internally Risk Graded, Recorded Investment	11,290	15,198
Performing [Member] | Substandard [Member] | Commercial [Member] | Healthcare [Member]
Recorded Investment [Abstract]
Internally Risk Graded, Recorded Investment	43,305	16,161
Performing [Member] | Substandard [Member] | Commercial [Member] | Other commercial and industrial [Member]
Recorded Investment [Abstract]
Internally Risk Graded, Recorded Investment	8,161	0
Performing [Member] | Substandard [Member] | Commercial Real Estate [Member]
Recorded Investment [Abstract]
Internally Risk Graded, Recorded Investment	827	5,309
Performing [Member] | Substandard [Member] | Commercial Real Estate [Member] | Residential construction and land development [Member]
Recorded Investment [Abstract]
Internally Risk Graded, Recorded Investment	395	470
Performing [Member] | Substandard [Member] | Commercial Real Estate [Member] | Retail [Member]
Recorded Investment [Abstract]
Internally Risk Graded, Recorded Investment	98	399
Performing [Member] | Substandard [Member] | Commercial Real Estate [Member] | Office [Member]
Recorded Investment [Abstract]
Internally Risk Graded, Recorded Investment	0	0
Performing [Member] | Substandard [Member] | Commercial Real Estate [Member] | Multifamily [Member]
Recorded Investment [Abstract]
Internally Risk Graded, Recorded Investment	48	4,434
Performing [Member] | Substandard [Member] | Commercial Real Estate [Member] | Industrial [Member]
Recorded Investment [Abstract]
Internally Risk Graded, Recorded Investment	0	0
Performing [Member] | Substandard [Member] | Commercial Real Estate [Member] | Other commercial real estate [Member]
Recorded Investment [Abstract]
Internally Risk Graded, Recorded Investment	286	6
Performing [Member] | Substandard [Member] | Residential Mortgage [Member]
Recorded Investment [Abstract]
Internally Risk Graded, Recorded Investment	822	2,331
Performing [Member] | Substandard [Member] | Residential Mortgage [Member] | Permanent mortgage [Member]
Recorded Investment [Abstract]
Internally Risk Graded, Recorded Investment	822	2,331
Performing [Member] | Substandard [Member] | Residential Mortgage [Member] | Permanent mortgages guaranteed by U.S. government agencies [Member]
Recorded Investment [Abstract]
Internally Risk Graded, Recorded Investment	0	0
Performing [Member] | Substandard [Member] | Residential Mortgage [Member] | Home equity [Member]
Recorded Investment [Abstract]
Internally Risk Graded, Recorded Investment	0	0
Performing [Member] | Substandard [Member] | Personal [Member]
Recorded Investment [Abstract]
Internally Risk Graded, Recorded Investment	63	1,054
Nonaccrual [Member]
Recorded Investment [Abstract]
Internally Risk Graded, Recorded Investment	141,334	185,930
Non-Graded, Recorded Investment	46,540	45,054
Nonaccrual [Member] | Commercial [Member]
Recorded Investment [Abstract]
Internally Risk Graded, Recorded Investment	137,233	178,895
Non-Graded, Recorded Investment	70	58
Nonaccrual [Member] | Commercial [Member] | Energy [Member]
Recorded Investment [Abstract]
Internally Risk Graded, Recorded Investment	92,284	132,499
Non-Graded, Recorded Investment	0	0
Nonaccrual [Member] | Commercial [Member] | Services [Member]
Recorded Investment [Abstract]
Internally Risk Graded, Recorded Investment	2,620	8,173
Non-Graded, Recorded Investment	0	0
Nonaccrual [Member] | Commercial [Member] | Wholesale/retail [Member]
Recorded Investment [Abstract]
Internally Risk Graded, Recorded Investment	2,574	11,407
Non-Graded, Recorded Investment	0	0
Nonaccrual [Member] | Commercial [Member] | Manufacturing [Member]
Recorded Investment [Abstract]
Internally Risk Graded, Recorded Investment	5,962	4,931
Non-Graded, Recorded Investment	0	0
Nonaccrual [Member] | Commercial [Member] | Healthcare [Member]
Recorded Investment [Abstract]
Internally Risk Graded, Recorded Investment	14,765	825
Non-Graded, Recorded Investment	0	0
Nonaccrual [Member] | Commercial [Member] | Other commercial and industrial [Member]
Recorded Investment [Abstract]
Internally Risk Graded, Recorded Investment	19,028	21,060
Non-Graded, Recorded Investment	70	58
Nonaccrual [Member] | Commercial Real Estate [Member]
Recorded Investment [Abstract]
Internally Risk Graded, Recorded Investment	2,855	5,521
Non-Graded, Recorded Investment	0	0
Nonaccrual [Member] | Commercial Real Estate [Member] | Residential construction and land development [Member]
Recorded Investment [Abstract]
Internally Risk Graded, Recorded Investment	1,832	3,433
Non-Graded, Recorded Investment	0	0
Nonaccrual [Member] | Commercial Real Estate [Member] | Retail [Member]
Recorded Investment [Abstract]
Internally Risk Graded, Recorded Investment	276	326
Non-Graded, Recorded Investment	0	0
Nonaccrual [Member] | Commercial Real Estate [Member] | Office [Member]
Recorded Investment [Abstract]
Internally Risk Graded, Recorded Investment	275	426
Non-Graded, Recorded Investment	0	0
Nonaccrual [Member] | Commercial Real Estate [Member] | Multifamily [Member]
Recorded Investment [Abstract]
Internally Risk Graded, Recorded Investment	0	38
Non-Graded, Recorded Investment	0	0
Nonaccrual [Member] | Commercial Real Estate [Member] | Industrial [Member]
Recorded Investment [Abstract]
Internally Risk Graded, Recorded Investment	0	76
Non-Graded, Recorded Investment	0	0
Nonaccrual [Member] | Commercial Real Estate [Member] | Other commercial real estate [Member]
Recorded Investment [Abstract]
Internally Risk Graded, Recorded Investment	472	1,222
Non-Graded, Recorded Investment	0	0
Nonaccrual [Member] | Residential Mortgage [Member]
Recorded Investment [Abstract]
Internally Risk Graded, Recorded Investment	1,163	1,417
Non-Graded, Recorded Investment	46,284	44,803
Nonaccrual [Member] | Residential Mortgage [Member] | Permanent mortgage [Member]
Recorded Investment [Abstract]
Internally Risk Graded, Recorded Investment	1,163	1,417
Non-Graded, Recorded Investment	24,030	21,438
Nonaccrual [Member] | Residential Mortgage [Member] | Permanent mortgages guaranteed by U.S. government agencies [Member]
Recorded Investment [Abstract]
Internally Risk Graded, Recorded Investment	0	0
Non-Graded, Recorded Investment	9,200	12,000
Nonaccrual [Member] | Residential Mortgage [Member] | Home equity [Member]
Recorded Investment [Abstract]
Internally Risk Graded, Recorded Investment	0	0
Non-Graded, Recorded Investment	13,075	11,519
Nonaccrual [Member] | Personal [Member]
Recorded Investment [Abstract]
Internally Risk Graded, Recorded Investment	83	97
Non-Graded, Recorded Investment	$ 186	$ 193

Loans and Allowances for Cred65

Loans and Allowances for Credit Losses, Impaired Loans (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017		Dec. 31, 2016
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	$ 438,459		$ 473,526
Impaired loans, recorded investment, total	376,201		418,525
Impaired loans, recorded investment with no related allowance	324,867		407,363
Impaired loans, recorded investment with related allowance	51,334		11,162
Impaired loans, related allowance	8,831		843
Impaired loans, average recorded investment	398,161		349,330
Impaired loans, interest income recognized	8,861		9,014
Impaired Loans, interest income recognized after charge-off recovery	7,200
Commercial [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	184,604		211,762
Impaired loans, recorded investment, total	137,303		178,953
Impaired loans, recorded investment with no related allowance	85,969		167,837
Impaired loans, recorded investment with related allowance	51,334		11,116
Impaired loans, related allowance	8,831		797
Impaired loans, average recorded investment	158,127		110,945
Impaired loans, interest income recognized	0		0
Commercial [Member] | Energy [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	111,011		146,897
Impaired loans, recorded investment, total	92,284		132,499
Impaired loans, recorded investment with no related allowance	40,968		121,418
Impaired loans, recorded investment with related allowance	51,316		11,081
Impaired loans, related allowance	8,814		762
Impaired loans, average recorded investment	112,392		80,100
Impaired loans, interest income recognized	0		0
Commercial [Member] | Services [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	5,324		11,723
Impaired loans, recorded investment, total	2,620		8,173
Impaired loans, recorded investment with no related allowance	2,620		8,173
Impaired loans, recorded investment with related allowance	0		0
Impaired loans, related allowance	0		0
Impaired loans, average recorded investment	5,396		9,232
Impaired loans, interest income recognized	0		0
Commercial [Member] | Wholesale/retail [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	9,099		17,669
Impaired loans, recorded investment, total	2,574		11,407
Impaired loans, recorded investment with no related allowance	2,574		11,407
Impaired loans, recorded investment with related allowance	0		0
Impaired loans, related allowance	0		0
Impaired loans, average recorded investment	6,990		7,163
Impaired loans, interest income recognized	0		0
Commercial [Member] | Manufacturing [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	6,073		5,320
Impaired loans, recorded investment, total	5,962		4,931
Impaired loans, recorded investment with no related allowance	5,962		4,931
Impaired loans, recorded investment with related allowance	0		0
Impaired loans, related allowance	0		0
Impaired loans, average recorded investment	5,446		2,631
Impaired loans, interest income recognized	0		0
Commercial [Member] | Healthcare [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	25,140		1,147
Impaired loans, recorded investment, total	14,765		825
Impaired loans, recorded investment with no related allowance	14,765		825
Impaired loans, recorded investment with related allowance	0		0
Impaired loans, related allowance	0		0
Impaired loans, average recorded investment	7,795		949
Impaired loans, interest income recognized	0		0
Commercial [Member] | Other commercial and industrial [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	27,957		29,006
Impaired loans, recorded investment, total	19,098		21,118
Impaired loans, recorded investment with no related allowance	19,080		21,083
Impaired loans, recorded investment with related allowance	18		35
Impaired loans, related allowance	17		35
Impaired loans, average recorded investment	20,108		10,870
Impaired loans, interest income recognized	0		0
Commercial Real Estate [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	4,751		14,427
Impaired loans, recorded investment, total	2,855		5,521
Impaired loans, recorded investment with no related allowance	2,855		5,521
Impaired loans, recorded investment with related allowance	0		0
Impaired loans, related allowance	0		0
Impaired loans, average recorded investment	4,189		7,262
Impaired loans, interest income recognized	0		0
Commercial Real Estate [Member] | Residential construction and land development [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	3,285		4,951
Impaired loans, recorded investment, total	1,832		3,433
Impaired loans, recorded investment with no related allowance	1,832		3,433
Impaired loans, recorded investment with related allowance	0		0
Impaired loans, related allowance	0		0
Impaired loans, average recorded investment	2,633		3,921
Impaired loans, interest income recognized	0		0
Commercial Real Estate [Member] | Retail [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	509		530
Impaired loans, recorded investment, total	276		326
Impaired loans, recorded investment with no related allowance	276		326
Impaired loans, recorded investment with related allowance	0		0
Impaired loans, related allowance	0		0
Impaired loans, average recorded investment	301		823
Impaired loans, interest income recognized	0		0
Commercial Real Estate [Member] | Office [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	287		521
Impaired loans, recorded investment, total	275		426
Impaired loans, recorded investment with no related allowance	275		426
Impaired loans, recorded investment with related allowance	0		0
Impaired loans, related allowance	0		0
Impaired loans, average recorded investment	351		539
Impaired loans, interest income recognized	0		0
Commercial Real Estate [Member] | Multifamily [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	0		1,000
Impaired loans, recorded investment, total	0		38
Impaired loans, recorded investment with no related allowance	0		38
Impaired loans, recorded investment with related allowance	0		0
Impaired loans, related allowance	0		0
Impaired loans, average recorded investment	19		156
Impaired loans, interest income recognized	0		0
Commercial Real Estate [Member] | Industrial [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	0		76
Impaired loans, recorded investment, total	0		76
Impaired loans, recorded investment with no related allowance	0		76
Impaired loans, recorded investment with related allowance	0		0
Impaired loans, related allowance	0		0
Impaired loans, average recorded investment	38		76
Impaired loans, interest income recognized	0		0
Commercial Real Estate [Member] | Other commercial real estate [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	670		7,349
Impaired loans, recorded investment, total	472		1,222
Impaired loans, recorded investment with no related allowance	472		1,222
Impaired loans, recorded investment with related allowance	0		0
Impaired loans, related allowance	0		0
Impaired loans, average recorded investment	847		1,747
Impaired loans, interest income recognized	0		0
Residential Mortgage [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	248,797		247,005
Impaired loans, recorded investment, total	235,774		233,761
Impaired loans, recorded investment with no related allowance	235,774		233,715
Impaired loans, recorded investment with related allowance	0		46
Impaired loans, related allowance	0		46
Impaired loans, average recorded investment	235,565		230,746
Impaired loans, interest income recognized	8,861		9,014
Residential Mortgage [Member] | Permanent mortgage [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	30,435		28,830
Impaired loans, recorded investment, total	25,193		22,855
Impaired loans, recorded investment with no related allowance	25,193		22,809
Impaired loans, recorded investment with related allowance	0		46
Impaired loans, related allowance	0		46
Impaired loans, average recorded investment	24,024		25,920
Impaired loans, interest income recognized	1,229		1,255
Residential Mortgage [Member] | Permanent mortgages guaranteed by U.S. government agencies [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	203,814	[1]	205,564	[2]
Impaired loans, recorded investment, total	197,506	[1]	199,387	[2]
Impaired loans, recorded investment with no related allowance	197,506	[1]	199,387	[2]
Impaired loans, recorded investment with related allowance	0	[1]	0	[2]
Impaired loans, related allowance	0	[1]	0	[2]
Impaired loans, average recorded investment	199,244	[1]	193,889	[2]
Impaired loans, interest income recognized	7,632	[1]	7,759	[2]
Residential Mortgage [Member] | Home equity [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	14,548		12,611
Impaired loans, recorded investment, total	13,075		11,519
Impaired loans, recorded investment with no related allowance	13,075		11,519
Impaired loans, recorded investment with related allowance	0		0
Impaired loans, related allowance	0		0
Impaired loans, average recorded investment	12,297		10,937
Impaired loans, interest income recognized	0		0
Personal [Member]
Impaired loans [Abstract]
Impaired loans, unpaid principal balance	307		332
Impaired loans, recorded investment, total	269		290
Impaired loans, recorded investment with no related allowance	269		290
Impaired loans, recorded investment with related allowance	0		0
Impaired loans, related allowance	0		0
Impaired loans, average recorded investment	280		377
Impaired loans, interest income recognized	$ 0		$ 0
[1]	All permanent mortgage loans guaranteed by U.S. government agencies are considered impaired as we do not expect full collection of contractual principal and interest. At December 31, 2017, $9.2 million of these loans are nonaccruing and $188 million are accruing based on the guarantee by U.S. government agencies.
[2]	All permanent mortgage loans guaranteed by U.S. government agencies are considered impaired as we do not expect full collection of contractual principal and interest. At December 31, 2016, $12 million of these loans are nonaccruing and $188 million are accruing based on the guarantee by U.S. government agencies.

Loans and Allowances for Cred66

Loans and Allowances for Credit Losses, Troubled Debt Restructurings (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	$ 126,000	$ 147,000
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	48,000	75,000
Troubled Debt Restructuring, Charge-offs	117	4,700
Troubled Debt Restructurings, Recorded Balance Modified During The Period	57,000	52,000
Accruing [Member] | Residential Mortgage [Member] | Permanent mortgages guaranteed by U.S. government agencies [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	$ 74,000	$ 81,000

Loans and Allowances for Cred67

Loans and Allowances for Credit Losses, By Aging Category (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Financing receivable, recorded investment, aging [Abstract]
Current	$ 16,770,208	$ 16,597,641
Nonaccrual	187,874	230,984
Total	17,153,424	16,989,660
Commercial [Member]
Financing receivable, recorded investment, aging [Abstract]
Current	10,575,384	10,205,838
Nonaccrual	137,303	178,953
Total	10,733,975	10,390,824
Commercial [Member] | Energy [Member]
Financing receivable, recorded investment, aging [Abstract]
Current	2,833,668	2,364,890
Nonaccrual	92,284	132,499
Total	2,930,156	2,497,868
Commercial [Member] | Services [Member]
Financing receivable, recorded investment, aging [Abstract]
Current	2,983,222	3,099,605
Nonaccrual	2,620	8,173
Total	2,986,949	3,108,990
Commercial [Member] | Wholesale/retail [Member]
Financing receivable, recorded investment, aging [Abstract]
Current	1,468,284	1,561,650
Nonaccrual	2,574	11,407
Total	1,471,256	1,576,818
Commercial [Member] | Manufacturing [Member]
Financing receivable, recorded investment, aging [Abstract]
Current	490,739	509,662
Nonaccrual	5,962	4,931
Total	496,774	514,975
Commercial [Member] | Healthcare [Member]
Financing receivable, recorded investment, aging [Abstract]
Current	2,284,770	2,201,050
Nonaccrual	14,765	825
Total	2,314,753	2,201,916
Commercial [Member] | Other commercial and industrial [Member]
Financing receivable, recorded investment, aging [Abstract]
Current	514,701	468,981
Nonaccrual	19,098	21,118
Total	534,087	490,257
Commercial Real Estate [Member]
Financing receivable, recorded investment, aging [Abstract]
Current	3,476,163	3,803,519
Nonaccrual	2,855	5,521
Total	3,479,987	3,809,046
Commercial Real Estate [Member] | Residential construction and land development [Member]
Financing receivable, recorded investment, aging [Abstract]
Current	115,213	132,100
Nonaccrual	1,832	3,433
Total	117,245	135,533
Commercial Real Estate [Member] | Retail [Member]
Financing receivable, recorded investment, aging [Abstract]
Current	691,256	761,562
Nonaccrual	276	326
Total	691,532	761,888
Commercial Real Estate [Member] | Office [Member]
Financing receivable, recorded investment, aging [Abstract]
Current	831,118	798,462
Nonaccrual	275	426
Total	831,770	798,888
Commercial Real Estate [Member] | Multifamily [Member]
Financing receivable, recorded investment, aging [Abstract]
Current	979,625	903,234
Nonaccrual	0	38
Total	980,017	903,272
Commercial Real Estate [Member] | Industrial [Member]
Financing receivable, recorded investment, aging [Abstract]
Current	573,014	871,673
Nonaccrual	0	76
Total	573,014	871,749
Commercial Real Estate [Member] | Other commercial real estate [Member]
Financing receivable, recorded investment, aging [Abstract]
Current	285,937	336,488
Nonaccrual	472	1,222
Total	286,409	337,716
Residential Mortgage [Member]
Financing receivable, recorded investment, aging [Abstract]
Current	1,754,287	1,749,473
Nonaccrual	47,447	46,220
Total	1,973,686	1,949,832
Residential Mortgage [Member] | Permanent mortgage [Member]
Financing receivable, recorded investment, aging [Abstract]
Current	1,014,588	979,386
Nonaccrual	25,193	22,855
Total	1,043,435	1,006,820
Residential Mortgage [Member] | Permanent mortgages guaranteed by U.S. government agencies [Member]
Financing receivable, recorded investment, aging [Abstract]
Current	22,692	40,594
Nonaccrual	9,179	11,846
Total	197,506	199,387
Residential Mortgage [Member] | Home equity [Member]
Financing receivable, recorded investment, aging [Abstract]
Current	717,007	729,493
Nonaccrual	13,075	11,519
Total	732,745	743,625
Personal [Member]
Financing receivable, recorded investment, aging [Abstract]
Current	964,374	838,811
Nonaccrual	269	290
Total	965,776	839,958
30 to 59 Days Past Due [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	41,991	28,603
30 to 59 Days Past Due [Member] | Commercial [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	16,215	4,968
30 to 59 Days Past Due [Member] | Commercial [Member] | Energy [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	0	479
30 to 59 Days Past Due [Member] | Commercial [Member] | Services [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	514	191
30 to 59 Days Past Due [Member] | Commercial [Member] | Wholesale/retail [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	398	3,761
30 to 59 Days Past Due [Member] | Commercial [Member] | Manufacturing [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	0	382
30 to 59 Days Past Due [Member] | Commercial [Member] | Healthcare [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	15,218	0
30 to 59 Days Past Due [Member] | Commercial [Member] | Other commercial and industrial [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	85	155
30 to 59 Days Past Due [Member] | Commercial Real Estate [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	476	6
30 to 59 Days Past Due [Member] | Commercial Real Estate [Member] | Residential construction and land development [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	200	0
30 to 59 Days Past Due [Member] | Commercial Real Estate [Member] | Retail [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	0	0
30 to 59 Days Past Due [Member] | Commercial Real Estate [Member] | Office [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	254	0
30 to 59 Days Past Due [Member] | Commercial Real Estate [Member] | Multifamily [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	22	0
30 to 59 Days Past Due [Member] | Commercial Real Estate [Member] | Industrial [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	0	0
30 to 59 Days Past Due [Member] | Commercial Real Estate [Member] | Other commercial real estate [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	0	6
30 to 59 Days Past Due [Member] | Residential Mortgage [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	24,619	23,040
30 to 59 Days Past Due [Member] | Residential Mortgage [Member] | Permanent mortgage [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	3,435	3,299
30 to 59 Days Past Due [Member] | Residential Mortgage [Member] | Permanent mortgages guaranteed by U.S. government agencies [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	18,978	17,465
30 to 59 Days Past Due [Member] | Residential Mortgage [Member] | Home equity [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	2,206	2,276
30 to 59 Days Past Due [Member] | Personal [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	681	589
60 to 89 Days Past Due [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	19,529	16,748
60 to 89 Days Past Due [Member] | Commercial [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	4,841	1,065
60 to 89 Days Past Due [Member] | Commercial [Member] | Energy [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	4,204	0
60 to 89 Days Past Due [Member] | Commercial [Member] | Services [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	486	1,021
60 to 89 Days Past Due [Member] | Commercial [Member] | Wholesale/retail [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	0	0
60 to 89 Days Past Due [Member] | Commercial [Member] | Manufacturing [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	73	0
60 to 89 Days Past Due [Member] | Commercial [Member] | Healthcare [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	0	41
60 to 89 Days Past Due [Member] | Commercial [Member] | Other commercial and industrial [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	78	3
60 to 89 Days Past Due [Member] | Commercial Real Estate [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	370	0
60 to 89 Days Past Due [Member] | Commercial Real Estate [Member] | Residential construction and land development [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	0	0
60 to 89 Days Past Due [Member] | Commercial Real Estate [Member] | Retail [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	0	0
60 to 89 Days Past Due [Member] | Commercial Real Estate [Member] | Office [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	0	0
60 to 89 Days Past Due [Member] | Commercial Real Estate [Member] | Multifamily [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	370	0
60 to 89 Days Past Due [Member] | Commercial Real Estate [Member] | Industrial [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	0	0
60 to 89 Days Past Due [Member] | Commercial Real Estate [Member] | Other commercial real estate [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	0	0
60 to 89 Days Past Due [Member] | Residential Mortgage [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	14,127	15,420
60 to 89 Days Past Due [Member] | Residential Mortgage [Member] | Permanent mortgage [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	219	1,280
60 to 89 Days Past Due [Member] | Residential Mortgage [Member] | Permanent mortgages guaranteed by U.S. government agencies [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	13,468	13,803
60 to 89 Days Past Due [Member] | Residential Mortgage [Member] | Home equity [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	440	337
60 to 89 Days Past Due [Member] | Personal [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	191	263
90 Days or More [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	133,822	115,684
90 Days or More [Member] | Commercial [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	232	0
90 Days or More [Member] | Commercial [Member] | Energy [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	0	0
90 Days or More [Member] | Commercial [Member] | Services [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	107	0
90 Days or More [Member] | Commercial [Member] | Wholesale/retail [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	0	0
90 Days or More [Member] | Commercial [Member] | Manufacturing [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	0	0
90 Days or More [Member] | Commercial [Member] | Healthcare [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	0	0
90 Days or More [Member] | Commercial [Member] | Other commercial and industrial [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	125	0
90 Days or More [Member] | Commercial Real Estate [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	123	0
90 Days or More [Member] | Commercial Real Estate [Member] | Residential construction and land development [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	0	0
90 Days or More [Member] | Commercial Real Estate [Member] | Retail [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	0	0
90 Days or More [Member] | Commercial Real Estate [Member] | Office [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	123	0
90 Days or More [Member] | Commercial Real Estate [Member] | Multifamily [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	0	0
90 Days or More [Member] | Commercial Real Estate [Member] | Industrial [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	0	0
90 Days or More [Member] | Commercial Real Estate [Member] | Other commercial real estate [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	0	0
90 Days or More [Member] | Residential Mortgage [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	133,206	115,679
90 Days or More [Member] | Residential Mortgage [Member] | Permanent mortgage [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	0	0
90 Days or More [Member] | Residential Mortgage [Member] | Permanent mortgages guaranteed by U.S. government agencies [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	133,189	115,679
90 Days or More [Member] | Residential Mortgage [Member] | Home equity [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	17	0
90 Days or More [Member] | Personal [Member]
Financing receivable, recorded investment, aging [Abstract]
Past Due	$ 261	$ 5

Premises and Equipment Premis68

Premises and Equipment Premises and Equipment (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Premises and Equipment [Line Items]
Premises and equipment	$ 755,824	$ 733,160
Less accumulated depreciation	438,489	407,311
Premises and equipment, net of accumulated depreciation	317,335	325,849
Depreciation Expense	48,000	40,000	$ 34,000
Land
Premises and Equipment [Line Items]
Premises and equipment	71,348	70,552
Buildings and improvements
Premises and Equipment [Line Items]
Premises and equipment	249,139	250,311
Software
Premises and Equipment [Line Items]
Premises and equipment	188,826	158,155
Furniture and equipment
Premises and Equipment [Line Items]
Premises and equipment	223,163	217,399
Construction in progress
Premises and Equipment [Line Items]
Premises and equipment	$ 23,348	$ 36,743

Goodwill and Intangible Asset69

Goodwill and Intangible Assets Acquisitions (Details) - MBT Bancshares [Member] - USD ($) $ in Thousands	Dec. 01, 2016	Dec. 31, 2017
Business Acquisition [Line Items]
Business Acquisition, Effective Date of Acquisition	Dec. 1, 2016
Purchase Price	$ 102,500
Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Intangibles		$ 2,000
Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Property, Plant, and Equipment		(1,500)
Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Goodwill		$ (526)

Goodwill and Intangible Asset70

Goodwill and Intangible Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017		Dec. 31, 2016
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, net	$ 28,658		$ 46,931
Finite-Lived Intangible Assets, Net, Amortization Expense, Fiscal Year Maturity [Abstract]
2,018	5,054
2,019	4,686
2,020	4,531
2,021	4,152
2,022	3,277
Thereafter	6,958
Goodwill [Roll Forward]
Goodwill, Gross Beginning Balance	449,127		385,689
Goodwill, Accumulated Impairment Beginning Balance	(228)		(228)
Goodwill, Net Beginning Balance	448,899		385,461
Goodwill recognized during period	4,301		69,496
Goodwill, decrease due to sale of consolidated merchant banking investments	(5,244)
Adjustment	(526)	[1]	(6,058)	[2]
Goodwill, Gross Ending Balance	447,658		449,127
Goodwill, Accumulated Impairment Ending Balance	(228)		(228)
Goodwill, Net Ending Balance	447,430		448,899
Commercial [Member]
Goodwill [Roll Forward]
Goodwill, Gross Beginning Balance	272,196		277,044
Goodwill, Accumulated Impairment Beginning Balance	0		0
Goodwill, Net Beginning Balance	272,196		277,044
Goodwill recognized during period	4,301		1,210
Goodwill, decrease due to sale of consolidated merchant banking investments	(5,219)
Adjustment	41,992	[1]	(6,058)	[2]
Goodwill, Gross Ending Balance	313,270		272,196
Goodwill, Accumulated Impairment Ending Balance	0		0
Goodwill, Net Ending Balance	313,270		272,196
Consumer [Member]
Goodwill [Roll Forward]
Goodwill, Gross Beginning Balance	39,251		39,251
Goodwill, Accumulated Impairment Beginning Balance	(228)		(228)
Goodwill, Net Beginning Balance	39,023		39,023
Goodwill recognized during period	0		0
Goodwill, decrease due to sale of consolidated merchant banking investments	0
Adjustment	4,435	[1]	0	[2]
Goodwill, Gross Ending Balance	43,686		39,251
Goodwill, Accumulated Impairment Ending Balance	(228)		(228)
Goodwill, Net Ending Balance	43,458		39,023
Wealth Management [Member]
Goodwill [Roll Forward]
Goodwill, Gross Beginning Balance	71,520		69,394
Goodwill, Accumulated Impairment Beginning Balance	0		0
Goodwill, Net Beginning Balance	71,520		69,394
Goodwill recognized during period	0		2,126
Goodwill, decrease due to sale of consolidated merchant banking investments	(25)
Adjustment	19,207	[1]	0	[2]
Goodwill, Gross Ending Balance	90,702		71,520
Goodwill, Accumulated Impairment Ending Balance	0		0
Goodwill, Net Ending Balance	90,702		71,520
Funds Management and Other [Member]
Goodwill [Roll Forward]
Goodwill, Gross Beginning Balance	66,160		0
Goodwill, Accumulated Impairment Beginning Balance	0		0
Goodwill, Net Beginning Balance	66,160		0
Goodwill recognized during period	0		66,160
Goodwill, decrease due to sale of consolidated merchant banking investments	0
Adjustment	(66,160)	[1]	0	[2]
Goodwill, Gross Ending Balance	0		66,160
Goodwill, Accumulated Impairment Ending Balance	0		0
Goodwill, Net Ending Balance	0		66,160
Core deposits premiums [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, gross	6,510		35,879
Accumulated amortization	808		29,369
Finite-lived intangible assets, net	5,702		6,510
Finite-Lived Intangible Assets, Net, Amortization Expense, Fiscal Year Maturity [Abstract]
2,018	732
2,019	716
2,020	697
2,021	675
2,022	649
Thereafter	2,233
Other identifiable intangible assets [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, gross	44,468		60,951
Accumulated amortization	21,512		20,530
Finite-lived intangible assets, net	22,956		$ 40,421
Finite-Lived Intangible Assets, Net, Amortization Expense, Fiscal Year Maturity [Abstract]
2,018	4,322
2,019	3,970
2,020	3,834
2,021	3,477
2,022	2,628
Thereafter	$ 4,725
[1]	Goodwill from Mobank acquisition was not yet allocated to the segments as of December 31, 2016. Adjustment was made in 2017 for final purchase price adjustments and to allocate to the segments.
[2]	Completion of an external audit of Heartland Food Products resulted in a reallocation of the purchase price between net assets acquired, intangible assets and goodwill during 2016.

Mortgage Banking Activities, Co

Mortgage Banking Activities, Components of Loans Held For Sale (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Schedule of Residential Mortgage Loans Held For Sale [Line Items]
Number of days for past due for a residential mortgage loan to be considered nonperforming (in days)	90 days	90 days
Residential mortgage loans held for sale, nonperforming	$ 0	$ 0
Credit losses recognized on residential mortgage loans held for sale	0	0
Components of Residential Mortgage Loans Held for Sale [Abstract]
Unpaid principal balance	212,525	286,414
Residential mortgage loans held for sale, Fair value	215,113	286,971
Total residential mortgages loans held for sale and mortgage loan commitments, net of forward sales contracts	$ 221,378	$ 301,897
Not Designated as Hedging Instrument [Member] | Residential mortgage loan commitments [Member]
Schedule of Residential Mortgage Loans Held For Sale [Line Items]
General number of days outstanding for residential mortgage commitments, minimum (in days)	60 days	60 days
General number of days outstanding for residential mortgage commitments, maximum (in days)	90 days	90 days
Components of Residential Mortgage Loans Held for Sale [Abstract]
Notional	$ 222,919	$ 318,359
Derivative, Net fair value	$ 6,523	$ 9,733
Not Designated as Hedging Instrument [Member] | Forward sales contracts [Member]
Schedule of Residential Mortgage Loans Held For Sale [Line Items]
General number of days for delivery of loans, for which the price is set by forward sales contracts, minimum (in days)	60 days	60 days
General number of days for delivery of loans, for which the price is set by forward sales contracts, maximum (in days)	90 days	90 days
Components of Residential Mortgage Loans Held for Sale [Abstract]
Notional	$ 380,159	$ 569,543
Derivative, Net fair value	$ (258)	$ 5,193

Mortgage Banking Activities, Mo

Mortgage Banking Activities, Mortgage Banking Revenue (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Mortgage Banking Revenue [Abstract]
Net realized gains on sales of mortgage loans	$ 45,128	$ 68,947	$ 67,407
Net change in unrealized gain on mortgage loans held for sale	2,031	(5,311)	(784)
Change in fair value of mortgage loan commitments	(3,210)	1,599	(1,837)
Net change in the fair value of forward sales contracts	(5,451)	4,393	4,801
Total mortgage Production Revenue	38,498	69,628	69,587
Servicing revenue	66,221	64,286	56,415
Mortgage banking revenue	$ 104,719	$ 133,914	$ 126,002

Mortgage Banking Activities, 73

Mortgage Banking Activities, Mortgage Servicing Rights (Details)	12 Months Ended
	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)
Summary of Mortgage Servicing Rights [Abstract]
Number of residential mortgage loans serviced for others	136,528	139,340	131,859
Outstanding principal balance of residential mortgage loans serviced for others	$ 22,046,632,000	$ 21,997,568,000	$ 19,678,226,000
Weighted average interest rate (in hundredths)	3.94%	3.97%	4.12%
Remaining contractual term (in months)	297 months	301 months	300 months
Servicing Asset at Fair Value, Amount [Roll Forward]
Beginning balance	$ 247,073,000	$ 218,605,000	$ 171,976,000
Additions, net	39,149,000	71,405,000	79,546,000
Change in fair value due to loan runoff	(33,527,000)	(40,744,000)	(28,064,000)
Change in fair value due to market changes	172,000	(2,193,000)	(4,853,000)
Ending balance	$ 252,867,000	$ 247,073,000	$ 218,605,000
Servicing Assets at Fair Value, Assumptions Used to Estimate Fair Value [Abstract]
Discount rate - risk-free rate plus a market premium (in hundredths)	9.84%	10.08%
Prepayment rate - based upon loan interest rate, original term and loan type, Minimum	8.72%	8.98%
Prepayment rate - based upon loan interest rate, original term and loan type, Maximum	15.16%	16.91%
Loan servicing costs - annually per loan based upon loan type, Performing, minimum (in dollars per loan)	$ 65	$ 63
Loan servicing costs - annually per loan based upon loan type, Performing, maximum (in dollars per loan)	88	120
Loan servicing costs - annually per loan based upon loan type, Delinquent loans, Minimum (in dollars per loan)	150	150
Loan servicing costs - annually per loan based upon loan type, Delinquent loans, Maximum (in dollars per loan)	500	500
Loan servicing costs - annually per loan based upon loan type, Loans in foreclosure, Minimum (in dollars per loan)	1,000	650
Loan servicing costs - annually per loan based upon loan type, Loans in foreclosure, Maximum (in dollars per loan)	$ 4,000	$ 4,250
Primary secondary mortgage rate spread	105	105
Escrow earnings rate - indexed to rates paid on deposit accounts with comparable average life (in hundredths)	2.24%	1.98%

Mortgage Banking Activities, Lo

Mortgage Banking Activities, Loans Serviced for Others (Details) $ in Thousands	Dec. 31, 2017USD ($)
Financing Receivable, Recorded Investment, Aging [Abstract]
Current	$ 21,474,814
30 To 59 Days Past Due	400,418
60 To 89 Days Past Due	89,631
90 Days or More Past Due	81,769
Total	22,046,632
FHLMC [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Current	7,995,369
30 To 59 Days Past Due	81,805
60 To 89 Days Past Due	14,091
90 Days or More Past Due	32,756
Total	8,124,021
FNMA [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Current	6,595,410
30 To 59 Days Past Due	81,405
60 To 89 Days Past Due	13,856
90 Days or More Past Due	27,083
Total	6,717,754
GNMA [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Current	6,431,808
30 To 59 Days Past Due	232,937
60 To 89 Days Past Due	60,556
90 Days or More Past Due	19,743
Total	6,745,044
Other [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Current	452,227
30 To 59 Days Past Due	4,271
60 To 89 Days Past Due	1,128
90 Days or More Past Due	2,187
Total	$ 459,813

Deposits (Details)

Deposits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Interest expense on deposits [Abstract]
Transaction deposits	$ 28,627	$ 13,906	$ 8,821
Savings	359	386	383
Time Deposit, Interest Expense [Abstract]
Certificates of deposits under $100,000	7,702	8,776	11,894
Certificates of deposits $100,000 and over	12,393	10,123	10,643
Other time deposits	4,722	7,303	12,429
Total time	24,817	26,202	34,966
Total	53,803	40,494	$ 44,170
Time Deposit Information [Abstract]
Time deposits in denomination of $250,000 or more	797,000	866,000
Time Deposit Maturities [Abstract]
2,018	1,200,000
2,019	221,000
2,020	86,000
2,021	102,000
2,022	132,000
Thereafter	307,000
Other Deposits Information [Abstract]
Overdrawn customer transaction deposits reclassified as loan balances	$ 5,900	$ 9,700

Other Borrowings (Details)

Other Borrowings (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Other Borrowings [Line Items]
Balance		$ 5,854,537	$ 5,717,302	$ 6,277,866
Average Balance		$ 6,559,101	$ 6,901,856	$ 5,880,647
Rate		1.18%	0.60%	0.36%
U.S. government agency mortgage-backed securities [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Amortized Cost		$ 525,452	$ 655,529
Fair Value		523,914	655,851
Repurchase Liability	[1]	$ 516,335	$ 668,661
Average Rate (in hundredths)		0.17%	0.02%
U.S. government agency mortgage-backed securities [Member] | Overnight [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Amortized Cost		$ 525,452	$ 655,529
Fair Value		523,914	655,851
Repurchase Liability	[1]	$ 516,335	$ 668,661
Average Rate (in hundredths)		0.17%	0.02%
U.S. government agency mortgage-backed securities [Member] | Long-term [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Amortized Cost		$ 0	$ 0
Fair Value		0	0
Repurchase Liability	[1]	$ 0	$ 0
Average Rate (in hundredths)		0.00%	0.00%
Parent [Member]
Other Borrowings [Line Items]
Balance		$ 144,677	$ 152,949	$ 0
Average Balance		$ 148,889	$ 77,112	$ 0
Rate		5.65%	5.86%	0.00%
Other borrowings, Maturities [Abstract]
2,018		$ 0
2,019		0
2,020		0
2,021		0
2,022		0
Thereafter		144,677
Parent [Member] | Other Borrowings [Member]
Other Borrowings [Line Items]
Balance		0	$ 8,309	$ 0
Average Balance		$ 4,231	$ 2,684	$ 0
Rate		7.00%	13.19%	0.00%
Parent [Member] | Trust preferred debt [Member]
Other Borrowings [Line Items]
Balance		$ 0	$ 7,217	$ 0
Rate		0.00%	3.28%	0.00%
Average Balance		$ 3,296	$ 611	$ 0
Rate		3.52%	3.27%	0.00%
Maximum Outstanding At Any Month End		$ 7,217	$ 7,217	$ 0
Parent [Member] | Trust preferred debt, 2003 issuance [Member]
Other Borrowings [Line Items]
Balance			$ 3,100
Other borrowings, Other Disclosures [Abstract]
Interest rate description			three-month LIBOR plus 2.95%
Parent [Member] | Trust preferred debt, 2006 issuance [Member]
Other Borrowings [Line Items]
Balance			$ 4,100
Other borrowings, Other Disclosures [Abstract]
Interest rate description			three-month LIBOR plus 1.82%
Parent [Member] | Other [Member]
Other Borrowings [Line Items]
Balance		$ 0	$ 1,092	$ 0
Rate		0.00%	8.27%	0.00%
Average Balance		$ 935	$ 2,073	$ 0
Rate		11.11%	16.11%	0.00%
Maximum Outstanding At Any Month End		$ 3,104	$ 3,157	$ 0
Parent [Member] | Subordinated debentures [Member]
Other Borrowings [Line Items]
Balance		$ 144,677	$ 144,640	$ 0
Rate		5.60%	5.60%	0.00%
Average Balance		$ 144,658	$ 74,428	$ 0
Rate		5.62%	5.59%	0.00%
Maximum Outstanding At Any Month End		$ 144,677	$ 145,393	$ 0
Parent [Member] | Subordinated debentures, 2016 issuance [Member]
Other borrowings, Other Disclosures [Abstract]
Amount of debt issuance		$ 150,000
Maturity date		Jun. 30, 2056
Stated interest rate		5.375%
Debt Instrument, Call Date, Earliest		Jun. 30, 2021
Subsidiaries [Member] | BOKF, NA [Member]
Other Borrowings [Line Items]
Balance		$ 5,709,860	5,564,353	6,277,866
Average Balance		$ 6,410,212	$ 6,824,744	$ 5,880,647
Rate		1.07%	0.54%	0.36%
Other borrowings, Maturities [Abstract]
2,018		$ 5,695,621
2,019		956
2,020		961
2,021		965
2,022		970
Thereafter		10,387
Subsidiaries [Member] | BOKF, NA [Member] | Funds purchased [Member]
Other Borrowings [Line Items]
Balance		$ 58,628	$ 57,929	$ 491,192
Rate		1.00%	0.38%	0.15%
Average Balance		$ 58,064	$ 78,222	$ 73,219
Rate		0.73%	0.24%	0.09%
Maximum Outstanding At Any Month End		$ 80,967	$ 567,103	$ 491,192
Other borrowings, Other Disclosures [Abstract]
Number of days to maturity, minimum		1 day
Number of days to maturity, maximum		90 days
Subsidiaries [Member] | BOKF, NA [Member] | Repurchase agreements [Member]
Other Borrowings [Line Items]
Balance		$ 516,335	$ 668,661	$ 722,444
Rate		0.17%	0.02%	0.02%
Average Balance		$ 433,791	$ 589,145	$ 623,921
Rate		0.10%	0.04%	0.04%
Maximum Outstanding At Any Month End		$ 536,094	$ 668,661	$ 1,008,144
Other borrowings, Other Disclosures [Abstract]
Number of days to maturity, maximum		90 days
Subsidiaries [Member] | BOKF, NA [Member] | Other Borrowings [Member]
Other Borrowings [Line Items]
Balance		$ 5,134,897	4,837,763	4,837,880
Average Balance		$ 5,918,357	$ 6,016,963	$ 4,957,175
Rate		1.14%	0.57%	0.33%
Subsidiaries [Member] | BOKF, NA [Member] | Federal Home Loan Bank advances [Member]
Other Borrowings [Line Items]
Balance		$ 5,100,000	$ 4,800,000	$ 4,800,000
Rate		1.47%	0.72%	0.48%
Average Balance		$ 5,882,466	$ 5,985,656	$ 4,921,739
Rate		1.13%	0.55%	0.28%
Maximum Outstanding At Any Month End		$ 6,200,000	$ 6,500,000	$ 5,000,000
Other borrowings, Other Disclosures [Abstract]
Federal Home Loan Banks, Letters of credit issued to secure public funds		272,000
Unused credit available pursuant to the FHLB's collateral policies		1,200,000
Subsidiaries [Member] | BOKF, NA [Member] | GNMA repurchase liability [Member]
Other Borrowings [Line Items]
Balance		$ 19,947	$ 22,471	$ 19,478
Rate		4.22%	4.26%	4.75%
Average Balance		$ 20,509	$ 15,637	$ 16,668
Rate		4.59%	4.74%	4.95%
Maximum Outstanding At Any Month End		$ 24,139	$ 22,471	$ 19,478
Subsidiaries [Member] | BOKF, NA [Member] | Other [Member]
Other Borrowings [Line Items]
Balance		$ 14,950	$ 15,292	$ 18,402
Rate		2.61%	2.66%	2.70%
Average Balance		$ 15,382	$ 15,670	$ 18,768
Rate		2.38%	2.41%	2.35%
Maximum Outstanding At Any Month End		$ 15,506	$ 15,797	$ 26,058
Subsidiaries [Member] | BOKF, NA [Member] | Subordinated debentures [Member]
Other Borrowings [Line Items]
Balance		$ 0	$ 0	$ 226,350
Rate		0.00%	0.00%	1.05%
Average Balance		$ 0	$ 140,414	$ 226,332
Rate		0.00%	1.35%	1.84%
Maximum Outstanding At Any Month End		$ 0	$ 226,434	$ 348,076
Subsidiaries [Member] | BOKF, NA [Member] | Subordinated debentures, 2007 issuance [Member]
Other Borrowings [Line Items]
Balance				226,000
Other borrowings, Other Disclosures [Abstract]
Amount of debt issuance				$ 250,000
Maturity date				May 15, 2017
Interest rate description				fixed rate of 5.75% through May 14, 2012 and is based on a floating rate of three-month LIBOR plus 0.69% thereafter
Subsidiaries [Member] | BOK Financial Securities, Inc. [Member] | Other [Member]
Other Borrowings [Line Items]
Balance		$ 0
[1]	BOK Financial maintains control over the securities underlying overnight repurchase agreements and generally transfers control over securities underlying longer-term dealer repurchase agreements to the respective counterparty.

Federal and State Income Taxe77

Federal and State Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Deferred tax assets [Abstract]
Available for sale securities mark to market	$ 12,083	$ 5,779
Share-based compensation	7,598	9,360
Credit loss allowances	58,666	99,191
Valuation adjustments	8,102	12,222
Deferred compensation	12,215	30,262
Unearned fees	9,265	11,877
Other	30,859	42,541
Total deferred tax assets	138,788	211,232
Valuation Allowance [Abstract]
Valuation allowance	0	0
Deferred tax liabilities [Abstract]
Depreciation	15,817	25,877
Mortgage servicing rights	63,112	92,748
Lease financing	9,973	17,923
Other	34,880	45,363
Total deferred tax liabilities	123,782	181,911
Net deferred tax assets	15,006	29,321
Current income tax expense [Abstract]
Federal	141,607	107,379	$ 117,566
State	14,592	11,028	12,397
Total current income tax expense	156,199	118,407	129,963
Deferred income tax expense [Abstract]
Federal	25,525	(11,340)	8,397
State	869	(690)	1,024
Total deferred income tax expense	26,394	(12,030)	9,421
Federal and state income taxes	182,593	106,377	139,384
Effective Income Tax Rate Reconciliation, Amount [Abstract]
Federal statutory tax	181,397	118,530	151,075
Tax exempt revenue	(12,402)	(10,544)	(9,553)
Effect of state income taxes, net of federal benefit	10,701	6,478	9,082
Utilization of tax credits: [Abstract]
Low-income housing tax credits, net of amortization	(5,356)	(4,171)	(3,874)
Other tax credits	(1,455)	(2,085)	(2,085)
Bank-owned life insurance	(3,121)	(2,911)	(3,264)
Share-based compensation	(2,817)	0	0
Revaluation of net deferred tax assets due to change in federal tax rates	9,456	0	0
Write-off of deferred tax assets related to executive compensation	2,216	0	0
Other, net	3,974	1,080	(1,997)
Federal and state income taxes	$ 182,593	$ 106,377	$ 139,384
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Federal statutory tax (in hundredths)	35.00%	35.00%	35.00%
Tax exempt revenue (in hundredths)	(2.40%)	(3.10%)	(2.20%)
Effect of state income taxes, net of federal benefit (in hundredths)	2.00%	1.90%	2.10%
Utilization of tax credits: [Abstract]
Low-income housing tax credits, net of amortization (in hundredths)	(1.00%)	(1.20%)	(0.90%)
Other tax credits (in hundredths)	(0.30%)	(0.60%)	(0.50%)
Bank-owned life insurance (in hundredths)	(0.60%)	(0.90%)	(0.70%)
Share-based compensation (in hundredths)	(0.50%)	0.00%	0.00%
Revaluation of net deferred tax assets due to change in federal tax rates (in hundredths)	1.80%	0.00%	0.00%
Write-off of deferred tax assets related to executive compensation (in hundredths)	0.40%	0.00%	0.00%
Other, net (in hundredths)	0.80%	0.30%	(0.50%)
Total (in hundredths)	35.20%	31.40%	32.30%
Income Tax Disclosures, Other Information [Abstract]
Expected Statutory Rate for 2018 and Beyond	21.00%
Pre-Tax Reform Combined Federal and State Statutory Rate	38.90%
Post-Tax Reform Combined Federal and State Statutory Rate	25.50%
Revaluation of Net Deferred Tax Assets Related to Temporary Differences in Accumulated Comprehensive Income	$ 6,400
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance as of January 1	15,841	$ 13,232	$ 13,374
Additions for tax for current year positions	4,645	5,640	2,226
Settlements during the period	0	0	0
Lapses of applicable statute of limitations	(2,376)	(3,031)	(2,368)
Balance as of December 31	18,110	15,841	13,232
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	12,200
Unrecognized Tax Benefits, Income Tax Penalties and Interest Expense	1,200	1,000	$ 1,000
Unrecognized Tax Benefits, Penalties and Interest Accrued	$ 4,000	$ 3,500
Unrecognized Tax Benefits, Number of Reporting Periods Open for Examination, Federal	3 years
Unrecognized Tax Benefits, Number of Reporting Periods Open for Examination, State, Minimum	3 years
Unrecognized Tax Benefits, Number of Reporting Periods Open for Examination, State, Maximum	6 years

Employee Benefits (Details)

Employee Benefits (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017		Dec. 31, 2016		Dec. 31, 2015
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Interest percentage added to the five-year trailing average of five-year Treasury Securities	1.50%
Interest percentage accrued on employee account balances, Minimum	3.00%
Interest percentage accrued on employee account balances, Maximum	5.00%
Interest percentage accrued on employee account balances for current year	3.00%
Change in projected benefit obligation [Roll Forward]
Projected benefit obligation at beginning of year	$ 34,964,000	[1],[2]	$ 38,797,000
Interest cost	1,153,000		1,309,000
Actuarial loss (gain)	223,000		(55,000)
Benefits paid	(5,443,000)		(5,087,000)
Projected benefit obligation at end of year	30,897,000	[1],[2]	34,964,000	[1],[2]	$ 38,797,000
Change in plan assets [Roll Forward]
Plan assets at fair value at beginning of year	41,769,000		44,190,000
Actual return on plan assets	4,093,000		2,666,000
Benefits paid	(5,443,000)		(5,087,000)
Plan assets at fair value at end of year	40,419,000		41,769,000		44,190,000
Defined Benefit Plan, Funded (Unfunded) Status of Plan [Abstract]
Funded status of the plan	9,522,000		6,805,000
Components of net periodic benefit costs [Abstract]
Interest cost	1,153,000		1,309,000
Expected return on plan assets	(2,041,000)		(2,167,000)
Other	184,000		(741,000)
Net periodic benefit cost (credit)	$ (704,000)		$ (1,599,000)
Weighted-average assumptions [Abstract]
Discount rate (in hundredths)	3.30%		3.43%
Expected return on plan assets (in hundredths)	5.50%		5.00%
Estimated Future Benefit Payments [Abstract]
2,018	$ 2,831,000
2,019	2,889,000
2,020	2,763,000
2,021	2,769,000
2,022	2,813,000
Thereafter	25,501,000
Total estimated future benefit payments	39,566,000
Defined Benefit Plan, Information about Plan Assets [Abstract]
Maximum tax deductible contributions to defined benefit plan	$ 10,000,000
Thrift Plan - Defined Contribution [Abstract]
Employee base compensation company match employee contributions (in hundredths)	6.00%
Employer matching rate for employee contributions minimum (in hundredths)	50.00%
Minimum years of service for employees to obtain maximum employer matching (in years)	4 years
Employer matching rate for employee contributions maximum (in hundredths)	200.00%
Maximum years of service for employees to obtain minimum employer matching (in years)	15 years
Non-elective annual contribution for qualified employees	$ 750
Annual base employee compensation to qualify for non-elective employer contributions maximum	$ 40,000
Vesting period for employer contributions (in years)	5 years
Thrift Plan expenses	$ 22,800,000		$ 22,400,000		$ 20,600,000
Equity Securities [Member]
Defined Benefit Plan, Information about Plan Assets [Abstract]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	60.00%
Bonds [Member]
Defined Benefit Plan, Information about Plan Assets [Abstract]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	40.00%
[1]	Projected benefit obligation equals accumulated benefit obligation.
[2]	Projected benefit obligation is based on January 1 measurement date.

Share-Based Compensation Plan79

Share-Based Compensation Plans (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	12 Months Ended
	Jan. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Stock Options [Member]
Share-based Compensation Arrangements by Share-based Payment Award, Options, Outstanding, Number of Options [Abstract]
Number of options outstanding, Beginning balance (in shares)	117,551	218,524	480,035	793,891
Options awarded (in shares)		0	0	0
Options exercised (in shares)		(99,556)	(249,404)	(286,678)
Options forfeited (in shares)		(624)	(4,098)	(22,304)
Options expired (in shares)		(793)	(8,009)	(4,874)
Number of options outstanding, Ending balance (in shares)		117,551	218,524	480,035
Options shares vested (in shares)		51,286	93,117	243,395
Share-based Compensation Arrangements by Share-based Payment Award, Options, Weighted Average Exercise Price [Abstract]
Options outstanding, weighted average exercise price, beginning balance (in dollars per share)	$ 53.26	$ 51.95	$ 49.75	$ 49.05
Options awarded, weighted average exercise price (in dollars per share)		0	0	0
Options exercised, weighted average exercise price (in dollars per share)		50.35	47.60	47.86
Options forfeited, weighted average exercise price (in dollars per share)		54.95	55.44	48.90
Options expired, weighted average exercise price (in dollars per share)		48.75	53.43	51.32
Options outstanding, weighted average exercise price, ending balance (in dollars per share)		53.26	51.95	49.75
Options vested, weighted average exercise price (in dollars per share)		$ 48.62	$ 46.22	$ 48.17
Share-based Compensation Arrangements by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Options outstanding, aggregate intrinsic value		$ 4,592	$ 6,793	$ 4,821	$ 8,725
Options vested, aggregate intrinsic value		2,241	3,429	2,829
Options exercised, aggregate intrinsic value		$ 3,500	$ 6,200	$ 5,100
Weighted average remaining contractual life of options outstanding (in years)		2 years 197 days
Weighted average remaining contractual life of options vested (in years)		1 year 58 days
Non-vested Common Stock [Member]
Share-based Compensation Arrangements by Share-based Payment Award, Restricted Stock, Nonvested, Number of Shares [Roll Forward]
Non-vested common shares awarded, beginning of period (in shares)	667,103	786,706	791,109	688,611
Non-vested shares that were granted during the period (in shares)		177,807	256,670	312,755
Non-vested shares that vested during period (in shares)		(194,419)	(213,941)	(114,045)
Non-vested shares that forfeited during period (in shares)		(102,991)	(47,132)	(96,212)
Non-vested common shares awarded, end of period (in shares)		667,103	786,706	791,109
Share-based Compensation Arrangements by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Roll Forward]
Weighted Average Grant Date Fair Value, Granted		$ 86.95	$ 55.35	$ 57.66
Weighted Average Grant Date Fair Value, Vested		63.07	55.87	50.15
Weighted average grant date fair value non-vested stock awards forfeited (in dollars per share)		$ 78.70	$ 57.86	$ 58.33
Share-based Compensation Costs, Including Costs That May Be Recognized As Future Expense [Abstract]
Share-based Compensation Expense Recognized		$ 23,200	$ 10,200	$ 12,000
Unrecognized compensation cost of unvested awards, for future periods		15,800
Unrecognized compensation cost of unvested awards, Amount to be expensed in 2018		9,900
Unrecognized compensation cost of unvested awards, Amount to be expensed in 2019		5,900
Unrecognized compensation cost of unvested awards, Amount to be expensed in 2020		$ 82
Total shares awarded under executive incentive plan (in shares)		296,518
Number of shares with required performance obligations		297,567
Subsequent Event [Member] | Non-vested Common Stock [Member]
Share-based Compensation Arrangements by Share-based Payment Award, Restricted Stock, Nonvested, Number of Shares [Roll Forward]
Non-vested shares that were granted during the period (in shares)	150,419
Share-based Compensation Arrangements by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Roll Forward]
Weighted Average Grant Date Fair Value, Granted	$ 94.77
Share-based Compensation Costs, Including Costs That May Be Recognized As Future Expense [Abstract]
Unrecognized compensation cost of unvested awards, for future periods	$ 14,300

Related Parties Related Parti80

Related Parties Related Parties (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Loans and Leases Receivable, Related Parties [Roll Forward]
Lease payments on office space in facilities owned by related party afffiliates	$ 27,500	$ 25,800	$ 25,200
Directors and Senior Management [Member]
Loans and Leases Receivable, Related Parties [Roll Forward]
Beginning balance	136,945	594,225
Advances	1,559,291	884,511
Payments	(1,585,865)	(1,123,747)
Adjustments	(125)	(218,044)
Ending balance	110,246	136,945	594,225
Board of Directors Chairman [Member]
Loans and Leases Receivable, Related Parties [Roll Forward]
Lease payments on office space in facilities owned by related party afffiliates	1,000	1,100	$ 975
Related Party Transaction, Amounts of Transaction	580
Director [Member]
Loans and Leases Receivable, Related Parties [Roll Forward]
Revenue from Related Parties	1,200
Related Party Transaction, Expenses from Transactions with Related Party	$ 8,300
Executive Officer [Member]
Loans and Leases Receivable, Related Parties [Roll Forward]
Percentage of investment funds' assets held by clients	93.00%
Assets Held in Cavanal Hill Funds	$ 3,700,000
Subsidiaries [Member] | BOKF, NA [Member] | Affiliated Entity [Member]
Loan Commitments and Equity Investments [Abstract]
Maximum percentage of unimpaired capital on loan commitments and equity investments to a single affiliate (in hundredths)	10.00%
Maximum percentage of unimpaired capital on loan commitments and equity investments to all affiliates (in hundredths)	20.00%
Maximum loan commitments and equity investments to a single affiliate	$ 310,000
Maximum loan commitments and equity investments to all affiliates	620,000
Largest loan commitment and equity investment to a single affiliate	223,000
Aggregate loan commitment and equity investment to all affiliates	323,000	337,000
Outstanding amounts to all affiliates	16,000	$ 39,000
Largest amount outstanding to a single affiliate	$ 12,000

Commitments and Contingent Li81

Commitments and Contingent Liabilities (Details)	12 Months Ended
	Dec. 31, 2017USD ($)shares	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)
Other Commitments [Abstract]
The Net Asset Value of Units in Mutual Funds (per unit)	1
Minimum Average Cash Balance Required to be Maintained at Federal Reserve by Subsidiary Bank	$ 1,900,000,000	$ 1,900,000,000
Operating Leases, Rent Expense, Net [Abstract]
Operating Leases, Rent Expense, Net	27,500,000	$ 25,800,000	$ 25,200,000
Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
Operating Leases, Future Minimum Payments, Due in 2018	18,900,000
Operating Leases, Future Minimum Payments, Due in 2019	19,300,000
Operating Leases, Future Minimum Payments, Due in 2020	17,100,000
Operating Leases, Future Minimum Payments, Due in 2021	15,000,000
Operating Leases, Future Minimum Payments, Due in 2022	9,700,000
Operating Leases, Future Minimum Payments, Due Thereafter	$ 73,000,000
Visa Membership [Member]
Loss Contingencies [Line Items]
Number of Visa Class B Shares Owned by Entity (in shares) | shares	252,233
Number of Visa Class A Shares Visa Class B Shares Are Convertible To (in shares) | shares	415,755
Misuse of Revenues Pledged to Municipal Bonds [Member] | Judicial Ruling [Member]
Litigation Settlement [Abstract]
Outstanding principal, accrued interest and other amounts required by bond documents	$ 48,000,000
Disgorged fees	1,067,721
Litigation Settlement, Expense	$ 600,000
Misuse of Revenues Pledged to Municipal Bonds [Member] | Pending Litigation [Member]
Litigation Settlement [Abstract]
Loss Contingency, Number of Plaintiffs	2
Bank Participation in Fraudulent Sale of Securities by Principals [Member] | Pending Litigation [Member]
Litigation Settlement [Abstract]
Loss Contingency, Number of Plaintiffs	19
Purchase of facilities from principals subject to SEC New Jersey proceedings [Member] | Pending Litigation [Member]
Litigation Settlement [Abstract]
Outstanding principal, accrued interest and other amounts required by bond documents	$ 60,000,000
Number of individuals who purchased facilities from the principals subject to SEC New Jersey proceedings	2
Number of principals in SEC New Jersey proceedings	2
County of Bernalillo [Member] [Domain] | Settled Litigation [Member]
Litigation Settlement [Abstract]
Loss Contingency, Damages Sought, Value	$ 5,600,000
Ownership of deposit accounts [Member] | Settled Litigation [Member]
Litigation Settlement [Abstract]
Litigation Settlement, Expense	$ 1,000,000
Loss Contingency, Number of Plaintiffs	2
Amount paid by the bank from creditor accounts to judgment creditor	$ 4,200,000
Loss Contingency, Damages Sought, Value	$ 7,000,000

Commitments and Contingent Li82

Commitments and Contingent Liabilities Variable Interest Entities (Details) $ in Thousands	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)
BOKF Equity, LLC [Member]
Variable Interest Entity [Line Items]
Number of Private Equity Funds of which the Entity is a General Partner	2
Contingent Obligation For Additional Investments In Private Equity Funds	$ 3,400
Loans [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Consolidated, Carrying Amount, Assets and Liabilities, Net	10,000	$ 10,000
Variable Interest Entity, Nonconsolidated, Carrying Amount, Assets and Liabilities, Net	52,852	44,488
Other Assets [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Consolidated, Carrying Amount, Assets and Liabilities, Net	26,787	58,725
Variable Interest Entity, Nonconsolidated, Carrying Amount, Assets and Liabilities, Net	191,903	175,390
Other Liabilities [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Consolidated, Carrying Amount, Assets and Liabilities, Net	0	3,189
Variable Interest Entity, Nonconsolidated, Carrying Amount, Assets and Liabilities, Net	70,827	78,357
Other borrowings [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Consolidated, Carrying Amount, Assets and Liabilities, Net	10,964	12,056
Variable Interest Entity, Nonconsolidated, Carrying Amount, Assets and Liabilities, Net	0	0
Non-Controlling Interests [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Consolidated, Carrying Amount, Assets and Liabilities, Net	22,967	31,503
Variable Interest Entity, Nonconsolidated, Carrying Amount, Assets and Liabilities, Net	0	0
Private Equity Funds Variable Interest Entities [Member] | Loans [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Consolidated, Carrying Amount, Assets and Liabilities, Net	0	0
Private Equity Funds Variable Interest Entities [Member] | Other Assets [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Consolidated, Carrying Amount, Assets and Liabilities, Net	14,783	17,357
Private Equity Funds Variable Interest Entities [Member] | Other Liabilities [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Consolidated, Carrying Amount, Assets and Liabilities, Net	0	0
Private Equity Funds Variable Interest Entities [Member] | Other borrowings [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Consolidated, Carrying Amount, Assets and Liabilities, Net	0	0
Private Equity Funds Variable Interest Entities [Member] | Non-Controlling Interests [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Consolidated, Carrying Amount, Assets and Liabilities, Net	11,927	13,237
Tax Credit Variable Interest Entities [Member] | Loans [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Consolidated, Carrying Amount, Assets and Liabilities, Net	10,000	10,000
Variable Interest Entity, Nonconsolidated, Carrying Amount, Assets and Liabilities, Net	52,852	44,488
Tax Credit Variable Interest Entities [Member] | Other Assets [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Consolidated, Carrying Amount, Assets and Liabilities, Net	10,964	11,585
Variable Interest Entity, Nonconsolidated, Carrying Amount, Assets and Liabilities, Net	153,506	143,715
Tax Credit Variable Interest Entities [Member] | Other Liabilities [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Consolidated, Carrying Amount, Assets and Liabilities, Net	0	0
Variable Interest Entity, Nonconsolidated, Carrying Amount, Assets and Liabilities, Net	47,859	63,329
Tax Credit Variable Interest Entities [Member] | Other borrowings [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Consolidated, Carrying Amount, Assets and Liabilities, Net	10,964	10,964
Variable Interest Entity, Nonconsolidated, Carrying Amount, Assets and Liabilities, Net	0	0
Tax Credit Variable Interest Entities [Member] | Non-Controlling Interests [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Consolidated, Carrying Amount, Assets and Liabilities, Net	10,000	10,000
Variable Interest Entity, Nonconsolidated, Carrying Amount, Assets and Liabilities, Net	0	0
Other Variable Interest Entities [Member] | Loans [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Consolidated, Carrying Amount, Assets and Liabilities, Net	0	0
Variable Interest Entity, Nonconsolidated, Carrying Amount, Assets and Liabilities, Net	0	0
Other Variable Interest Entities [Member] | Other Assets [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Consolidated, Carrying Amount, Assets and Liabilities, Net	1,040	29,783
Variable Interest Entity, Nonconsolidated, Carrying Amount, Assets and Liabilities, Net	38,397	31,675
Other Variable Interest Entities [Member] | Other Liabilities [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Consolidated, Carrying Amount, Assets and Liabilities, Net	0	3,189
Variable Interest Entity, Nonconsolidated, Carrying Amount, Assets and Liabilities, Net	22,968	15,028
Other Variable Interest Entities [Member] | Other borrowings [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Consolidated, Carrying Amount, Assets and Liabilities, Net	0	1,092
Variable Interest Entity, Nonconsolidated, Carrying Amount, Assets and Liabilities, Net	0	0
Other Variable Interest Entities [Member] | Non-Controlling Interests [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Consolidated, Carrying Amount, Assets and Liabilities, Net	1,040	8,266
Variable Interest Entity, Nonconsolidated, Carrying Amount, Assets and Liabilities, Net	$ 0	$ 0

Earnings Per Share (Details)

Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Numerator: [Abstract]:
Net income attributable to BOK Financial Corp. shareholders	$ 334,644	$ 232,668	$ 288,565
Less: Earnings allocated to participating securities	3,561	2,883	3,383
Numerator for basic earnings per share - income available to common shareholders	331,083	229,785	285,182
Effect of reallocating undistributed earnings of participating securities	(2)	(1)	(3)
Numerator for diluted earnings per share - income available to common shareholders	$ 331,085	$ 229,786	$ 285,185
Denominator: [Abstract]
Weighted average shares outstanding	65,440,832	65,901,110	68,397,215
Less: Participating securities included in weighted average shares outstanding (in shares)	695,468	815,483	802,526
Denominator for basic earnings per common share (in shares)	64,745,364	65,085,627	67,594,689
Dilutive effect of employee stock compensation plans (in shares)	60,920	58,271	96,969
Denominator for diluted earnings per common share (in shares)	64,806,284	65,143,898	67,691,658
Basic (in dollars per share)	$ 5.11	$ 3.53	$ 4.22
Diluted earnings per share (per share)	$ 5.11	$ 3.53	$ 4.21
Excludes employee stock options with exercise prices greater than current market price.	0	0	0

Shareholders' Equity (Details)

Shareholders' Equity (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Common Stock [Abstract]
Common stock, authorized (in shares)	2,500,000,000	2,500,000,000
Common stock, par value (in dollars per share)	$ 0.00006	$ 0.00006
Perpetual preferred stock [Member]
Preferred Stock [Abstract]
Preferred stock, authorized (in shares)	1,000,000,000
Preferred stock at par value (in dollars per share)	$ 0.00005
Preferred stock conversion rate	one share of Common Stock for each 36 shares of Series A Preferred Stock at the option of the holder
Preferred stock, Rate of annual cumulative dividends (in hundredths)	10.00%
Preferred stock, Liquidation preference per share	$ 0.06
Preferred stock, Aggregate liquidation preference	$ 15
Preferred Stock, Shares Outstanding	0	0	0
Common Stock [Member]
Common Stock [Abstract]
Common stock, authorized (in shares)	2,500,000,000
Common stock, par value (in dollars per share)	$ 0.00006
Common stock, number of vote per share	$ 1

Shareholders' Equity Regulatory

Shareholders' Equity Regulatory Capital (Details) - USD ($) $ in Thousands		Dec. 31, 2017	Dec. 31, 2016
Common Equity Tier 1 Capital [Abstract]
Minimum Capital Requirement, Common Equity Tier 1 Capital to Risk Weighted Assets		4.50%
Capital Conservation Buffer, Common Equity Tier 1 to Risk Weighted Assets	[1]	2.50%
Minimum Capital Requirement Including Capital Conservation Buffer, Common Equity Tier 1 to Risk Weighted Assets		7.00%
Common Equity Tier 1 Capital		$ 3,074,981	$ 2,834,532
Common Equity Tier 1 Capital to Risk Weighted Assets		12.05%	11.21%
Tier I Capital (to Risk Weighted Assets) [Abstract]
Minimum Capital Requirement, Tier 1 Capital to Risk Weighted Assets		6.00%
Capital Conservation Buffer, Tier 1 Capital to Risk Weighted Assets	[1]	2.50%
Minimum Capital Requirement Including Capital Conservation Buffer, Tier One to Risk Weighted Assets		8.50%
Tier 1 Capital		$ 3,074,981	$ 2,834,532
Tier 1 Capital to Risk Weighted Assets		12.05%	11.21%
Total Capital (to Risk Weighted Assets) [Abstract]
Minimum Capital Requirement, Total Capital to Risk Weighted Assets		8.00%
Capital Conservation Buffer, Total Capital to Risk Weighted Assets	[1]	2.50%
Minimum Capital Requirement Including Capital Conservation Buffer, Total Capital to Risk Weighted Assets		10.50%
Total Capital		$ 3,455,709	$ 3,238,323
Total Capital to Risk Weighted Assets		13.54%	12.81%
Tier 1 Capital (to Average Assets) [Abstract]
Minimum Capital Requirement, Tier 1 Capital to Average Assets		4.00%
Minimum Capital Requirements Including Capital Conservation Buffer, Tier 1 Capital to Average Assets		4.00%
Tier 1 Leverage Capital		$ 3,074,981	$ 2,834,532
Tier 1 Capital to Average Assets		9.31%	8.72%
Phased in Capital Conservation Buffer		1.25%	0.625%
Fully Phased In Capital Conservation Buffer		2.50%
Subsidiaries [Member] | BOKF, NA [Member]
Common Equity Tier 1 Capital [Abstract]
Common Equity Tier 1 Capital Ratio Required to be Well Capitalized		6.50%
Minimum Capital Requirement, Common Equity Tier 1 Capital to Risk Weighted Assets		4.50%
Minimum Capital Requirement Including Capital Conservation Buffer, Common Equity Tier 1 to Risk Weighted Assets		4.50%
Common Equity Tier 1 Capital		$ 2,870,694	$ 2,609,450
Common Equity Tier 1 Capital to Risk Weighted Assets		11.34%	10.65%
Tier I Capital (to Risk Weighted Assets) [Abstract]
Tier I Capital Ratio Required to be Well Capitalized		8.00%
Minimum Capital Requirement, Tier 1 Capital to Risk Weighted Assets		6.00%
Minimum Capital Requirement Including Capital Conservation Buffer, Tier One to Risk Weighted Assets		6.00%
Tier 1 Capital		$ 2,870,694	$ 2,609,450
Tier 1 Capital to Risk Weighted Assets		11.34%	10.65%
Total Capital (to Risk Weighted Assets) [Abstract]
Total Capital Ratio Required to be Well Capitalized		10.00%
Minimum Capital Requirement, Total Capital to Risk Weighted Assets		8.00%
Minimum Capital Requirement Including Capital Conservation Buffer, Total Capital to Risk Weighted Assets		8.00%
Total Capital		$ 3,105,117	$ 2,866,949
Total Capital to Risk Weighted Assets		12.27%	11.70%
Tier 1 Capital (to Average Assets) [Abstract]
Leverage Ratio Required to be Well Capitalized		5.00%
Minimum Capital Requirement, Tier 1 Capital to Average Assets		4.00%
Minimum Capital Requirements Including Capital Conservation Buffer, Tier 1 Capital to Average Assets		4.00%
Tier 1 Leverage Capital		$ 2,870,694	$ 2,609,450
Tier 1 Capital to Average Assets		8.73%	8.11%
Subsidiaries [Member] | Mobank [Member]
Common Equity Tier 1 Capital [Abstract]
Common Equity Tier 1 Capital Ratio Required to be Well Capitalized	[2]	6.50%
Minimum Capital Requirement, Common Equity Tier 1 Capital to Risk Weighted Assets	[2]	4.50%
Minimum Capital Requirement Including Capital Conservation Buffer, Common Equity Tier 1 to Risk Weighted Assets	[2]	4.50%
Common Equity Tier 1 Capital	[2]		$ 54,616
Common Equity Tier 1 Capital to Risk Weighted Assets	[2]		10.03%
Tier I Capital (to Risk Weighted Assets) [Abstract]
Tier I Capital Ratio Required to be Well Capitalized	[2]	8.00%
Minimum Capital Requirement, Tier 1 Capital to Risk Weighted Assets	[2]	6.00%
Minimum Capital Requirement Including Capital Conservation Buffer, Tier One to Risk Weighted Assets	[2]	6.00%
Tier 1 Capital	[2]		$ 54,616
Tier 1 Capital to Risk Weighted Assets	[2]		10.03%
Total Capital (to Risk Weighted Assets) [Abstract]
Total Capital Ratio Required to be Well Capitalized	[2]	10.00%
Minimum Capital Requirement, Total Capital to Risk Weighted Assets	[2]	8.00%
Minimum Capital Requirement Including Capital Conservation Buffer, Total Capital to Risk Weighted Assets	[2]	8.00%
Total Capital	[2]		$ 54,617
Total Capital to Risk Weighted Assets	[2]		10.03%
Tier 1 Capital (to Average Assets) [Abstract]
Leverage Ratio Required to be Well Capitalized	[2]	5.00%
Minimum Capital Requirement, Tier 1 Capital to Average Assets	[2]	4.00%
Minimum Capital Requirements Including Capital Conservation Buffer, Tier 1 Capital to Average Assets	[2]	4.00%
Tier 1 Leverage Capital	[2]		$ 54,616
Tier 1 Capital to Average Assets	[2]		8.37%
[1]	Capital conservation buffer is effective January 1, 2016 and is phased in through 2019. The phased in capital conservation buffer was 1.25% at December 31, 2017 and 0.625% at December 31, 2016. The fully phased in requirement of 2.50% is included in the table above.
[2]	Missouri Bank and Trust Company of Kansas City dba Mobank was acquired by BOK Financial effective December 1, 2016 and was merged into BOKF, NA effective February 17, 2017.

Shareholders' Equity Accumulate

Shareholders' Equity Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance		$ (10,967)	$ 21,587	$ 56,673
Net change in unrealized gain (loss)		(26,152)	(41,521)	(46,803)
Reclassification adjustments included in earnings: [Abstract]
Interest revenue, Investment securities, Taxable securities		0	(112)	(503)
Interest expense, Subordinated debentures		0	0	121
Net impairment losses recognized in earnings		0	0	1,819
Gain on available for sale securities, net		(4,428)	(11,675)	(12,058)
Other comprehensive income (loss), before income taxes		(30,580)	(53,308)	(57,424)
Federal and state income taxes	[1]	(11,923)	(20,754)	(22,338)
Other comprehensive income (loss), net of income taxes		(18,657)	(32,554)	(35,086)
Reclassification of stranded accumulated other comprehensive loss to retained earnings related to tax reform		(6,550)
Ending balance		(36,174)	(10,967)	21,587
Unrealized Gain (Loss) on Available for Sale Securities [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance		(9,087)	23,284	59,239
Net change in unrealized gain (loss)		(28,170)	(41,333)	(48,607)
Reclassification adjustments included in earnings: [Abstract]
Interest revenue, Investment securities, Taxable securities		0	0	0
Interest expense, Subordinated debentures		0	0	0
Net impairment losses recognized in earnings		0	0	1,819
Gain on available for sale securities, net		(4,428)	(11,675)	(12,058)
Other comprehensive income (loss), before income taxes		(32,598)	(53,008)	(58,846)
Federal and state income taxes	[1]	(12,708)	(20,637)	(22,891)
Other comprehensive income (loss), net of income taxes		(19,890)	(32,371)	(35,955)
Reclassification of stranded accumulated other comprehensive loss to retained earnings related to tax reform		(6,408)
Ending balance		(35,385)	(9,087)	23,284
Unrealized Gain (Loss) on Available for Sale Securities [Member] | Perpetual Preferred, Equity Securities and Mutual Funds [Member]
Reclassification adjustments included in earnings: [Abstract]
Ending balance		2,700
Unrealized Gain (Loss) on Investment Securities Transferred from AFS [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance		0	68	376
Net change in unrealized gain (loss)		0	0	0
Reclassification adjustments included in earnings: [Abstract]
Interest revenue, Investment securities, Taxable securities		0	(112)	(503)
Interest expense, Subordinated debentures		0	0	0
Net impairment losses recognized in earnings		0	0	0
Gain on available for sale securities, net		0	0	0
Other comprehensive income (loss), before income taxes		0	(112)	(503)
Federal and state income taxes	[1]	0	(44)	(195)
Other comprehensive income (loss), net of income taxes		0	(68)	(308)
Reclassification of stranded accumulated other comprehensive loss to retained earnings related to tax reform		0
Ending balance		0	0	68
Unrealized Gain (Loss) on Employee Benefit Plans [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance		(1,880)	(1,765)	(2,868)
Net change in unrealized gain (loss)		2,018	(188)	1,804
Reclassification adjustments included in earnings: [Abstract]
Interest revenue, Investment securities, Taxable securities		0	0	0
Interest expense, Subordinated debentures		0	0	0
Net impairment losses recognized in earnings		0	0	0
Gain on available for sale securities, net		0	0	0
Other comprehensive income (loss), before income taxes		2,018	(188)	1,804
Federal and state income taxes	[1]	785	(73)	701
Other comprehensive income (loss), net of income taxes		1,233	(115)	1,103
Reclassification of stranded accumulated other comprehensive loss to retained earnings related to tax reform		(142)
Ending balance		(789)	(1,880)	(1,765)
Loss on Effective Cash Flow Hedges [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance		0	0	(74)
Net change in unrealized gain (loss)		0	0	0
Reclassification adjustments included in earnings: [Abstract]
Interest revenue, Investment securities, Taxable securities		0	0	0
Interest expense, Subordinated debentures		0	0	121
Net impairment losses recognized in earnings		0	0	0
Gain on available for sale securities, net		0	0	0
Other comprehensive income (loss), before income taxes		0	0	121
Federal and state income taxes	[1]	0	0	47
Other comprehensive income (loss), net of income taxes		0	0	74
Reclassification of stranded accumulated other comprehensive loss to retained earnings related to tax reform		0
Ending balance		0	$ 0	$ 0
Retained Earnings [Member]
Reclassification adjustments included in earnings: [Abstract]
Reclassification of stranded accumulated other comprehensive loss to retained earnings related to tax reform		$ 6,550
[1]	Calculated using 39% effective tax rate.

Reportable Segments (Details)

Reportable Segments (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Net interest and dividend revenue from external sources	$ 841,701	$ 747,228	$ 703,354
Net interest revenue (expense) from internal sources	0	0	0
Net interest and dividend revenue	841,701	747,228	703,354
Provision for credit losses	(7,000)	65,000	34,000
Net interest and dividend revenue after provision for credit losses	848,701	682,228	669,354
Other operating revenue	695,094	674,020	658,480
Other operating expense	1,025,517	1,017,590	896,191
Net direct contribution	518,278	338,658	431,643
Gain (loss) on financial instruments, net	0	0	0
Change in fair value of mortgage servicing rights	0	0	0
Gain (loss) on repossessed assets, net	0	0	0
Corporate expense allocations	0	0	0
Net income before taxes	518,278	338,658	431,643
Federal and state income taxes	182,593	106,377	139,384
Net income	335,685	232,281	292,259
Net income (loss) attributable to non-controlling interests	1,041	(387)	3,694
Net income attributable to BOK Financial Corp. shareholders	334,644	232,668	288,565
Average assets	32,947,494	32,278,402	30,574,755
Operating Segments [Member] | Commercial [Member]
Segment Reporting Information [Line Items]
Net interest and dividend revenue from external sources	588,938	492,967	439,751
Net interest revenue (expense) from internal sources	(84,290)	(58,781)	(52,313)
Net interest and dividend revenue	504,648	434,186	387,438
Provision for credit losses	13,881	32,959	(6,748)
Net interest and dividend revenue after provision for credit losses	490,767	401,227	394,186
Other operating revenue	206,110	195,521	177,729
Other operating expense	226,334	216,451	202,804
Net direct contribution	470,543	380,297	369,111
Gain (loss) on financial instruments, net	52	10	0
Change in fair value of mortgage servicing rights	0	0	0
Gain (loss) on repossessed assets, net	(2,681)	669	708
Corporate expense allocations	33,958	35,760	43,279
Net income before taxes	433,956	345,216	326,540
Federal and state income taxes	168,809	134,289	127,024
Net income	265,147	210,927	199,516
Net income (loss) attributable to non-controlling interests	0	0	0
Net income attributable to BOK Financial Corp. shareholders	265,147	210,927	199,516
Average assets	17,517,217	16,998,626	16,284,527
Operating Segments [Member] | Consumer [Member]
Segment Reporting Information [Line Items]
Net interest and dividend revenue from external sources	96,360	85,998	84,848
Net interest revenue (expense) from internal sources	47,218	37,777	28,503
Net interest and dividend revenue	143,578	123,775	113,351
Provision for credit losses	4,783	4,927	6,934
Net interest and dividend revenue after provision for credit losses	138,795	118,848	106,417
Other operating revenue	196,231	224,802	218,095
Other operating expense	224,323	249,744	203,070
Net direct contribution	110,703	93,906	121,442
Gain (loss) on financial instruments, net	(3,331)	(26,252)	(4,712)
Change in fair value of mortgage servicing rights	172	(2,193)	(4,853)
Gain (loss) on repossessed assets, net	223	979	916
Corporate expense allocations	67,761	66,411	74,936
Net income before taxes	40,006	29	37,857
Federal and state income taxes	15,562	11	14,726
Net income	24,444	18	23,131
Net income (loss) attributable to non-controlling interests	0	0	0
Net income attributable to BOK Financial Corp. shareholders	24,444	18	23,131
Average assets	8,956,713	8,722,372	8,836,327
Operating Segments [Member] | Wealth Management [Member]
Segment Reporting Information [Line Items]
Net interest and dividend revenue from external sources	45,024	33,006	24,744
Net interest revenue (expense) from internal sources	38,344	29,043	24,043
Net interest and dividend revenue	83,368	62,049	48,787
Provision for credit losses	(696)	(801)	(1,083)
Net interest and dividend revenue after provision for credit losses	84,064	62,850	49,870
Other operating revenue	301,434	283,222	267,523
Other operating expense	246,626	250,994	228,664
Net direct contribution	138,872	95,078	88,729
Gain (loss) on financial instruments, net	0	(42)	(204)
Change in fair value of mortgage servicing rights	0	0	0
Gain (loss) on repossessed assets, net	387	0	0
Corporate expense allocations	40,562	42,378	40,357
Net income before taxes	98,697	52,658	48,168
Federal and state income taxes	38,393	20,484	18,737
Net income	60,304	32,174	29,431
Net income (loss) attributable to non-controlling interests	0	0	0
Net income attributable to BOK Financial Corp. shareholders	60,304	32,174	29,431
Average assets	7,072,622	6,281,127	5,444,483
Funds Management and Other [Member]
Segment Reporting Information [Line Items]
Net interest and dividend revenue from external sources	111,379	135,257	154,011
Net interest revenue (expense) from internal sources	(1,272)	(8,039)	(233)
Net interest and dividend revenue	110,107	127,218	153,778
Provision for credit losses	(24,968)	27,915	34,897
Net interest and dividend revenue after provision for credit losses	135,075	99,303	118,881
Other operating revenue	(8,681)	(29,525)	(4,867)
Other operating expense	328,234	300,401	261,653
Net direct contribution	(201,840)	(230,623)	(147,639)
Gain (loss) on financial instruments, net	3,279	26,284	4,916
Change in fair value of mortgage servicing rights	(172)	2,193	4,853
Gain (loss) on repossessed assets, net	2,071	(1,648)	(1,624)
Corporate expense allocations	(142,281)	(144,549)	(158,572)
Net income before taxes	(54,381)	(59,245)	19,078
Federal and state income taxes	(40,171)	(48,407)	(21,103)
Net income	(14,210)	(10,838)	40,181
Net income (loss) attributable to non-controlling interests	1,041	(387)	3,694
Net income attributable to BOK Financial Corp. shareholders	(15,251)	(10,451)	36,487
Average assets	$ (599,058)	$ 276,277	$ 9,418

Fair Value Measurements, Fair V

Fair Value Measurements, Fair Value Of Financial Instruments as Measured On a Recurring Basis (Details) - USD ($) $ in Thousands	Dec. 31, 2017		Dec. 31, 2016		Dec. 31, 2015	Dec. 31, 2014
Assets [Abstract]
Trading securities	$ 462,676		$ 337,628
Available for sale securities	8,321,578		8,676,829
Fair value option securities	755,054		77,046
Mortgage servicing rights	252,867		247,073		$ 218,605	$ 171,976
Derivative contracts, net of cash margin, Assets, Fair Value	220,502		689,872
Liabilities [Abstract]
Derivative contracts, net of cash margin, Liabilities, Fair Value	171,963		664,531
U.S. government agency debentures [Member]
Assets [Abstract]
Trading securities	21,196		6,234
U.S. government agency residential mortgage-backed securities [Member]
Assets [Abstract]
Trading securities	392,673		310,067
Available for sale securities	5,309,152		5,460,386
Fair value option securities	755,054		77,046
Municipal and other tax-exempt securities [Member]
Assets [Abstract]
Trading securities	13,559		14,427
Available for sale securities	27,080		40,993
Other trading securities [Member]
Assets [Abstract]
Trading securities	11,363		6,900
U.S. Treasury securities [Member]
Assets [Abstract]
Available for sale securities	1,000		999
Privately issued residential mortgage-backed securities [Member]
Assets [Abstract]
Available for sale securities	93,221		115,535
Commercial mortgage-backed securities guaranteed by U.S. government agencies [Member]
Assets [Abstract]
Available for sale securities	2,834,961		3,017,933
Other debt securities [Member]
Assets [Abstract]
Available for sale securities	25,481		4,152
Perpetual preferred stock [Member]
Assets [Abstract]
Available for sale securities	15,767		18,474
Equity securities and mutual funds [Member]
Assets [Abstract]
Available for sale securities	14,916		18,357
Fair Value, Measurements, Recurring [Member]
Assets [Abstract]
Trading securities	462,676		337,628
Available for sale securities	8,321,578		8,676,829
Residential mortgage loans held for sale	221,378		301,897
Mortgage servicing rights	252,867	[1]	247,073	[2]
Derivative contracts, net of cash margin, Assets, Fair Value	220,502	[3]	689,872	[4]
Liabilities [Abstract]
Derivative contracts, net of cash margin, Liabilities, Fair Value	171,963	[3]	664,531	[4]
Fair Value, Measurements, Recurring [Member] | U.S. government agency debentures [Member]
Assets [Abstract]
Trading securities	21,196		6,234
Fair Value, Measurements, Recurring [Member] | U.S. government agency residential mortgage-backed securities [Member]
Assets [Abstract]
Trading securities	392,673		310,067
Available for sale securities	5,309,152		5,460,386
Fair value option securities	755,054		77,046
Fair Value, Measurements, Recurring [Member] | Municipal and other tax-exempt securities [Member]
Assets [Abstract]
Trading securities	13,559		14,427
Available for sale securities	27,080		40,993
Fair Value, Measurements, Recurring [Member] | Asset-backed securities [Member]
Assets [Abstract]
Trading securities	23,885		0
Fair Value, Measurements, Recurring [Member] | Other trading securities [Member]
Assets [Abstract]
Trading securities	11,363		6,900
Fair Value, Measurements, Recurring [Member] | U.S. Treasury securities [Member]
Assets [Abstract]
Available for sale securities	1,000		999
Fair Value, Measurements, Recurring [Member] | Privately issued residential mortgage-backed securities [Member]
Assets [Abstract]
Available for sale securities	93,221		115,535
Fair Value, Measurements, Recurring [Member] | Commercial mortgage-backed securities guaranteed by U.S. government agencies [Member]
Assets [Abstract]
Available for sale securities	2,834,961		3,017,933
Fair Value, Measurements, Recurring [Member] | Other debt securities [Member]
Assets [Abstract]
Available for sale securities	25,481		4,152
Fair Value, Measurements, Recurring [Member] | Perpetual preferred stock [Member]
Assets [Abstract]
Available for sale securities	15,767		18,474
Fair Value, Measurements, Recurring [Member] | Equity securities and mutual funds [Member]
Assets [Abstract]
Available for sale securities	14,916		18,357
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Assets [Abstract]
Trading securities	0		0
Available for sale securities	1,000		4,494
Residential mortgage loans held for sale	0		0
Mortgage servicing rights	0	[1]	0	[2]
Derivative contracts, net of cash margin, Assets, Fair Value	8,179	[3]	7,541	[4]
Liabilities [Abstract]
Derivative contracts, net of cash margin, Liabilities, Fair Value	0	[3]	6,972	[4]
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | U.S. government agency debentures [Member]
Assets [Abstract]
Trading securities	0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | U.S. government agency residential mortgage-backed securities [Member]
Assets [Abstract]
Trading securities	0		0
Available for sale securities	0		0
Fair value option securities	0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Municipal and other tax-exempt securities [Member]
Assets [Abstract]
Trading securities	0		0
Available for sale securities	0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Asset-backed securities [Member]
Assets [Abstract]
Trading securities	0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Other trading securities [Member]
Assets [Abstract]
Trading securities	0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | U.S. Treasury securities [Member]
Assets [Abstract]
Available for sale securities	1,000		999
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Privately issued residential mortgage-backed securities [Member]
Assets [Abstract]
Available for sale securities	0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Commercial mortgage-backed securities guaranteed by U.S. government agencies [Member]
Assets [Abstract]
Available for sale securities	0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Other debt securities [Member]
Assets [Abstract]
Available for sale securities	0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Perpetual preferred stock [Member]
Assets [Abstract]
Available for sale securities	0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Equity securities and mutual funds [Member]
Assets [Abstract]
Available for sale securities	0		3,495
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Assets [Abstract]
Trading securities	462,676		337,628
Available for sale securities	8,315,304		8,662,394
Residential mortgage loans held for sale	209,079		290,280
Mortgage servicing rights	0	[1]	0	[2]
Derivative contracts, net of cash margin, Assets, Fair Value	212,323	[3]	682,331	[4]
Liabilities [Abstract]
Derivative contracts, net of cash margin, Liabilities, Fair Value	171,963	[3]	657,559	[4]
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | U.S. government agency debentures [Member]
Assets [Abstract]
Trading securities	21,196		6,234
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | U.S. government agency residential mortgage-backed securities [Member]
Assets [Abstract]
Trading securities	392,673		310,067
Available for sale securities	5,309,152		5,460,386
Fair value option securities	755,054		77,046
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Municipal and other tax-exempt securities [Member]
Assets [Abstract]
Trading securities	13,559		14,427
Available for sale securities	22,278		35,204
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Asset-backed securities [Member]
Assets [Abstract]
Trading securities	23,885		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Other trading securities [Member]
Assets [Abstract]
Trading securities	11,363		6,900
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | U.S. Treasury securities [Member]
Assets [Abstract]
Available for sale securities	0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Privately issued residential mortgage-backed securities [Member]
Assets [Abstract]
Available for sale securities	93,221		115,535
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Commercial mortgage-backed securities guaranteed by U.S. government agencies [Member]
Assets [Abstract]
Available for sale securities	2,834,961		3,017,933
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Other debt securities [Member]
Assets [Abstract]
Available for sale securities	25,009		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Perpetual preferred stock [Member]
Assets [Abstract]
Available for sale securities	15,767		18,474
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Equity securities and mutual funds [Member]
Assets [Abstract]
Available for sale securities	14,916		14,862
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Assets [Abstract]
Trading securities	0		0
Available for sale securities	5,274		9,941
Residential mortgage loans held for sale	12,299		11,617
Mortgage servicing rights	252,867	[1]	247,073	[2]
Derivative contracts, net of cash margin, Assets, Fair Value	0	[3]	0	[4]
Liabilities [Abstract]
Derivative contracts, net of cash margin, Liabilities, Fair Value	0	[3]	0	[4]
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | U.S. government agency debentures [Member]
Assets [Abstract]
Trading securities	0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | U.S. government agency residential mortgage-backed securities [Member]
Assets [Abstract]
Trading securities	0		0
Available for sale securities	0		0
Fair value option securities	0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Municipal and other tax-exempt securities [Member]
Assets [Abstract]
Trading securities	0		0
Available for sale securities	4,802		5,789
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Asset-backed securities [Member]
Assets [Abstract]
Trading securities	0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Other trading securities [Member]
Assets [Abstract]
Trading securities	0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | U.S. Treasury securities [Member]
Assets [Abstract]
Available for sale securities	0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Privately issued residential mortgage-backed securities [Member]
Assets [Abstract]
Available for sale securities	0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Commercial mortgage-backed securities guaranteed by U.S. government agencies [Member]
Assets [Abstract]
Available for sale securities	0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Other debt securities [Member]
Assets [Abstract]
Available for sale securities	472		4,152
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Perpetual preferred stock [Member]
Assets [Abstract]
Available for sale securities	0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Equity securities and mutual funds [Member]
Assets [Abstract]
Available for sale securities	$ 0		$ 0
[1]	A reconciliation of the beginning and ending fair value of mortgage servicing rights and disclosures of significant assumptions used to determine fair value are presented in Note 7, Mortgage Banking Activities.
[2]	A reconciliation of the beginning and ending fair value of mortgage servicing rights and disclosures of significant assumptions used to determine fair value are presented in Note 7, Mortgage Banking Activities.
[3]	See Note 3 for detail of fair value of derivative contracts by contract type. Derivative contracts in a net asset position that were valued based on quoted prices in active markets or identical instruments (Level 1) are exchange-traded interest rate, energy and agricultural derivative contracts, net of cash margin. Derivative contracts in a net liability position that were valued using quoted prices in active markets for identical instruments (Level 1) are exchange-traded interest rate and energy derivative contracts, fully offset by cash margin.
[4]	See Note 3 for detail of fair value of derivative contracts by contract type. Derivative contracts in a net asset position that were valued based on quoted prices in active markets for identical instruments (Level 1) are exchange-traded interest rate and energy derivative contracts, net of cash margin. Derivative contracts in a net liability position that were valued using quoted prices in active markets for identical instruments based on quoted prices in active markets for identical instruments (Level 1) are exchange-traded interest rate, energy and agricultural derivative contracts, net of cash margin.

Fair Value Measurements, Measur

Fair Value Measurements, Measured On Recurring Basis Significant Unobservable Inputs (Details) - Fair Value, Measurements, Recurring [Member] - Fair Value, Inputs, Level 3 [Member] - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016
Available for sale securities [Member] | Municipal and other tax-exempt securities [Member]
Fair Value Assets Measured on Recurring Basis Unobservable Reconciliation [Roll Forward]
Balance at beginning of period		$ 5,789	$ 9,610
Transfers to Level 3 from Level 2		0	0
Purchases and capital calls		0	0
Redemptions and distributions		(1,100)	(3,975)
Proceeds from sales		0	0
Other comprehensive income (loss)		113	154
Balance at end of period		4,802	5,789
Available for sale securities [Member] | Municipal and other tax-exempt securities [Member] | Mortgage banking revenue [Member]
Fair Value Assets Measured on Recurring Basis Unobservable Reconciliation [Roll Forward]
Gain (loss) recognized in earnings		0	0
Available for sale securities [Member] | Other debt securities [Member]
Fair Value Assets Measured on Recurring Basis Unobservable Reconciliation [Roll Forward]
Balance at beginning of period		4,152	4,151
Transfers to Level 3 from Level 2		0	0
Purchases and capital calls		0	0
Redemptions and distributions		0	0
Proceeds from sales		(3,900)	0
Other comprehensive income (loss)		220	1
Balance at end of period		472	4,152
Available for sale securities [Member] | Other debt securities [Member] | Mortgage banking revenue [Member]
Fair Value Assets Measured on Recurring Basis Unobservable Reconciliation [Roll Forward]
Gain (loss) recognized in earnings		0	0
Residential mortgage loans held for sale [Member]
Fair Value Assets Measured on Recurring Basis Unobservable Reconciliation [Roll Forward]
Balance at beginning of period		11,617	7,874
Transfers to Level 3 from Level 2	[1]	3,507	6,631
Purchases and capital calls		0	0
Redemptions and distributions		0	0
Proceeds from sales		(2,944)	(2,540)
Other comprehensive income (loss)		0	0
Balance at end of period		12,299	11,617
Residential mortgage loans held for sale [Member] | Mortgage banking revenue [Member]
Fair Value Assets Measured on Recurring Basis Unobservable Reconciliation [Roll Forward]
Gain (loss) recognized in earnings		$ 119	$ (348)
[1]	Recurring transfers to Level 3 from Level 2 consist of residential mortgage loans intended for sale to U.S. government agencies that fail to meet conforming standards.

Fair Value Measurements Fair Va

Fair Value Measurements Fair Value Measurements, Financial Instruments Measured On a Recurring Basis, Quantitative Information (Details) - Fair Value, Measurements, Recurring [Member] - Fair Value, Inputs, Level 3 [Member] - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017		Dec. 31, 2016
Available for sale securities [Member] | Municipal and other tax-exempt securities [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Par Value		$ 5,095		$ 6,195
Amortized Cost		5,068		6,163
Fair Value		$ 4,802		$ 5,789
Valuation Techniques		Discounted cash flows	[1]	Discounted cash flows	[2]
Significant Unobservable Input		Interest rate spread		Interest rate spread
Discount Rate, Minimum		6.60%	[3]	5.91%	[4]
Discount Rate, Maximum		6.60%	[3]	6.21%	[4]
Discount Rate, Weighted Average		6.60%	[3]	6.16%	[4]
Fair Value As Percentage of Par Value or Principal Balance, Minimum	[5]	92.25%		90.00%
Fair Value As Percentage of Par Value or Principal Balance, Maximum	[5]	94.76%		93.40%
Fair Value As Percentage of Par Value or Unpaid Principal Balance, Weighted Average	[5]	93.75%		92.20%
Investment Grade Tax Exempt Securities Yield Spread Over Comparable Securities, Minimum		372		467
Investment Grade Tax Exempt Securities Yield Spread Over Comparable Securities, Maximum		466		525
Available for sale securities [Member] | Other debt securities [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Par Value		$ 500		$ 4,400
Amortized Cost		500		4,400
Fair Value		$ 472		$ 4,152
Valuation Techniques		Discounted cash flows	[1]	Discounted cash flows	[2]
Significant Unobservable Input		Interest rate spread		Interest rate spread
Discount Rate, Minimum		6.85%	[6]	6.01%	[7]
Discount Rate, Maximum		6.85%	[6]	6.26%	[7]
Discount Rate, Weighted Average		6.85%	[6]	6.23%	[7]
Fair Value As Percentage of Par Value or Principal Balance, Minimum		94.39%	[5]	94.34%	[8]
Fair Value As Percentage of Par Value or Principal Balance, Maximum		94.39%	[5]	94.36%	[8]
Fair Value As Percentage of Par Value or Unpaid Principal Balance, Weighted Average		94.39%	[5]	94.36%	[8]
Average Yields On Comparable Short-term Taxable Securities		3.00%		1.00%
Residential mortgage loans held for sale [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Amortized Cost		$ 12,981		$ 12,431
Fair Value		$ 12,299		$ 11,617
Valuation Techniques		Quoted prices of loans sold in securitization transactions, with a liquidity discount applied		Quoted prices of loans sold in securitization transactions, with a liquidity discount applied
Significant Unobservable Input		Liquidity discount applied to the market value of mortgage loans qualifying for sale to U.S. government agencies		Liquidity discount applied to the market value of mortgage loans qualifying for sale to U.S. government agencies
Fair Value As Percentage of Par Value or Principal Balance, Minimum		94.75%		93.45%
Fair Value As Percentage of Par Value or Principal Balance, Maximum		94.75%		93.45%
Fair Value As Percentage of Par Value or Unpaid Principal Balance, Weighted Average		94.75%		93.45%
[1]	Discounted cash flows developed using discount rates primarily based on reference to interest rate spreads for comparable securities of similar duration and credit rating as determined by the nationally-recognized rating agencies, adjusted for lack of trading volume.
[2]	1 Discounted cash flows developed using discount rates primarily based on reference to interest rate spreads for comparable securities of similar duration and credit rating as determined by the nationally-recognized rating agencies, adjusted for lack of trading volume.
[3]	Interest rate yields used to value investment grade tax-exempt securities represent a spread of 372 to 466 basis points over average yields for comparable tax-exempt securities.
[4]	Interest rate yields used to value investment grade tax-exempt securities represent a spread of 467 to 525 basis points over average yields for comparable tax-exempt securities.
[5]	Represents fair value as a percentage of par value.
[6]	Interest rate yields used to value investment grade taxable securities based on comparable short-term taxable securities which are generally yielding approximately 3%.
[7]	Interest rate yields used to value investment grade taxable securities based on comparable short-term taxable securities which are generally yielding less than 1%.
[8]	Represents fair value as a percentage of par value.

Fair Value Measurements, Fair91

Fair Value Measurements, Fair Value Measured On a Nonrecurring Basis (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	$ 40,419	$ 41,769	$ 44,190
Fair Value, Measurements, Nonrecurring [Member] | Impaired Loans [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Gross charge-offs against allowance for loan losses	12,145	7,594
Net losses and expenses of repossessed assets, net	0	0
Fair Value, Measurements, Nonrecurring [Member] | Real estate and other repossessed assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Gross charge-offs against allowance for loan losses	0	0
Net losses and expenses of repossessed assets, net	6,372	2,527
Fair Value, Measurements, Nonrecurring [Member] | Fair Value, Inputs, Level 1 [Member] | Impaired Loans [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	0	0
Fair Value, Measurements, Nonrecurring [Member] | Fair Value, Inputs, Level 1 [Member] | Real estate and other repossessed assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	0	0
Fair Value, Measurements, Nonrecurring [Member] | Fair Value, Inputs, Level 2 [Member] | Impaired Loans [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	7,436	539
Fair Value, Measurements, Nonrecurring [Member] | Fair Value, Inputs, Level 2 [Member] | Real estate and other repossessed assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	3,483	7,965
Fair Value, Measurements, Nonrecurring [Member] | Fair Value, Inputs, Level 3 [Member] | Impaired Loans [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	7,626	11,295
Fair Value, Measurements, Nonrecurring [Member] | Fair Value, Inputs, Level 3 [Member] | Real estate and other repossessed assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	5,481	2,192
Pension Plan [Member] | Fair Value, Measurements, Nonrecurring [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	$ 40,000	$ 42,000

Fair Value Measurements Fair 92

Fair Value Measurements Fair Value Measurement, Measured On Non-Recurring Basis, Signfiicant Unobservable Inputs, Quantitative Information (Details) - Fair Value, Measurements, Nonrecurring [Member] - Fair Value, Inputs, Level 3 [Member] - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016
Impaired Loans [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value		$ 7,626	$ 11,295
Valuation Techniques		Discounted cash flows	Discounted cash flows
Significant Unobservable Input		Recoverable oil and gas reserves, forward-looking commodity prices and estimated operating costs	Recoverable oil and gas reserves, forward-looking commodity prices and estimated operating costs
Fair Value of Impaired Loans as a Percentage of Unpaid Principal Balance [Abstract]
Fair Value of Impaired Loans as a Percentage of Unpaid Principal Balance, Minimum	[1]	40.00%	22.00%
Fair Value of Impaired Loans as a Percentage of Unpaid Principal Balance, Maximum	[1]	86.00%	59.00%
Fair Value of Impaired Loans as a Percentage of Unpaid Principal Balance, Weighted Average	[1]	59.00%	57.00%
Real estate and other repossessed assets [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value		$ 5,481	$ 2,192
Valuation Techniques		Discounted cash flows	Appraised value, as adjusted
Significant Unobservable Input		Recoverable oil and gas reserves, forward-looking commodity prices, estimated operating costs	Marketability adjustments off appraised value2	[2]
Fair Value of Real Estate and Other Repossessed Assets as a Percentage of Appraised Value [Abstract]
Fair Value of Real Estate and Other Repossessed Assets, Percentage of Appraised Value, Minimum			70.00%
Fair Value of Real Estate and Other Repossessed Assets, Percentage of Appraised Value, Maximum			87.00%
Fair Value of Real Estate and Other Repossessed Assets, Percentage of Appraised Value, Weighted Average			74.00%
[1]	Represents fair value as a percentage of the unpaid principal balance.
[2]	Marketability adjustments include consideration of estimated costs to sell which is approximately 10% of the fair value.

Fair Value Measurements, Financ

Fair Value Measurements, Financial Instruments (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Trading securities	$ 462,676	$ 337,628
Investment securities	461,793	546,145
Available for sale securities	8,321,578	8,676,829
Fair value option securities	755,054	77,046
Residential mortgage loans held for sale	221,378	301,897
Loans	17,153,424	16,989,660
Allowance for loan losses	(230,682)	(246,159)	$ (225,524)	$ (189,056)
Loans, net of allowance	16,922,742	16,743,501
Mortgage servicing rights	252,867	247,073	218,605	171,976
Derivative contracts, net of cash margin, Assets, Fair Value	220,502	689,872
Time deposits	2,098,416	2,221,800
Subordinated debentures	144,677	144,640
Derivative contracts, net of cash margin, Liabilities, Fair Value	171,963	664,531
Fair Value Assumptions and Methodology for Assets and Liabilities [Abstract]
Specific allocation of allowance for loan losses included in fair value of loans	208,000	218,000
Commercial [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans	10,733,975	10,390,824
Allowance for loan losses	(124,269)	(140,213)	(130,334)	(90,875)
Commercial Real Estate [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans	3,479,987	3,809,046
Allowance for loan losses	(56,621)	(50,749)	(41,391)	(42,445)
Residential Mortgage [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans	1,973,686	1,949,832
Allowance for loan losses	(18,451)	(18,224)	(19,509)	(23,458)
Personal [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans	965,776	839,958
Allowance for loan losses	(9,124)	(8,773)	$ (4,164)	$ (4,233)
U.S. government agency debentures [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Trading securities	21,196	6,234
U.S. government agency residential mortgage-backed securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Trading securities	392,673	310,067
Available for sale securities	5,309,152	5,460,386
Fair value option securities	755,054	77,046
Municipal and other tax-exempt securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Trading securities	13,559	14,427
Investment securities	228,186	320,364
Available for sale securities	27,080	40,993
Other trading securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Trading securities	11,363	6,900
U.S. Treasury securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale securities	1,000	999
Privately issued residential mortgage-backed securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale securities	93,221	115,535
Commercial mortgage-backed securities guaranteed by U.S. government agencies [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale securities	2,834,961	3,017,933
Other debt securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investment securities	217,716	205,004
Available for sale securities	25,481	4,152
Perpetual preferred stock [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale securities	15,767	18,474
Equity securities and mutual funds [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale securities	14,916	18,357
Carrying (Reported) Amount, Fair Value Disclosure [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and due from banks	602,510	620,846
Interest-bearing cash and cash equivalents	1,714,544	1,916,651
Trading securities	462,676	337,628
Investment securities	461,793	546,145
Available for sale securities	8,321,578	8,676,829
Residential mortgage loans held for sale	221,378	301,897
Loans	17,153,424	16,989,660
Allowance for loan losses	(230,682)	(246,159)
Loans, net of allowance	16,922,742	16,743,501
Mortgage servicing rights	252,867	247,073
Derivative contracts, net of cash margin, Assets, Fair Value	220,502	689,872
Deposits with no stated maturity	19,962,889	20,526,295
Time deposits	2,098,416	2,221,800
Other borrowed funds	5,709,860	5,572,662
Subordinated debentures	144,677	144,640
Derivative contracts, net of cash margin, Liabilities, Fair Value	171,963	664,531
Carrying (Reported) Amount, Fair Value Disclosure [Member] | Commercial [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans	10,733,975	10,390,824
Carrying (Reported) Amount, Fair Value Disclosure [Member] | Commercial Real Estate [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans	3,479,987	3,809,046
Carrying (Reported) Amount, Fair Value Disclosure [Member] | Residential Mortgage [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans	1,973,686	1,949,832
Carrying (Reported) Amount, Fair Value Disclosure [Member] | Personal [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans	965,776	839,958
Carrying (Reported) Amount, Fair Value Disclosure [Member] | U.S. government agency debentures [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Trading securities	21,196	6,234
Carrying (Reported) Amount, Fair Value Disclosure [Member] | U.S. government agency residential mortgage-backed securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Trading securities	392,673	310,067
Investment securities	15,891	20,777
Available for sale securities	5,309,152	5,460,386
Fair value option securities	755,054	77,046
Carrying (Reported) Amount, Fair Value Disclosure [Member] | Municipal and other tax-exempt securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Trading securities	13,559	14,427
Investment securities	228,186	320,364
Available for sale securities	27,080	40,993
Carrying (Reported) Amount, Fair Value Disclosure [Member] | Asset-backed securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Trading securities	23,885	0
Carrying (Reported) Amount, Fair Value Disclosure [Member] | Other trading securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Trading securities	11,363	6,900
Carrying (Reported) Amount, Fair Value Disclosure [Member] | U.S. Treasury securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale securities	1,000	999
Carrying (Reported) Amount, Fair Value Disclosure [Member] | Privately issued residential mortgage-backed securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale securities	93,221	115,535
Carrying (Reported) Amount, Fair Value Disclosure [Member] | Commercial mortgage-backed securities guaranteed by U.S. government agencies [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale securities	2,834,961	3,017,933
Carrying (Reported) Amount, Fair Value Disclosure [Member] | Other debt securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investment securities	217,716	205,004
Available for sale securities	25,481	4,152
Carrying (Reported) Amount, Fair Value Disclosure [Member] | Perpetual preferred stock [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale securities	15,767	18,474
Carrying (Reported) Amount, Fair Value Disclosure [Member] | Equity securities and mutual funds [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale securities	14,916	18,357
Estimate of Fair Value, Fair Value Disclosure [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and due from banks	602,510	620,846
Interest-bearing cash and cash equivalents	1,714,544	1,916,651
Trading securities	438,791	337,628
Investment securities	480,035	565,493
Available for sale securities	8,321,578	8,676,829
Residential mortgage loans held for sale	221,378	301,897
Loans	16,887,787	17,178,060
Allowance for loan losses	0	0
Loans, net of allowance	16,887,787	17,178,060
Mortgage servicing rights	252,867	247,073
Derivative contracts, net of cash margin, Assets, Fair Value	220,502	689,872
Deposits with no stated maturity	19,962,889	20,526,295
Time deposits	2,064,558	2,218,303
Other borrowed funds	5,703,121	5,556,327
Subordinated debentures	148,207	128,903
Derivative contracts, net of cash margin, Liabilities, Fair Value	171,963	664,531
Estimate of Fair Value, Fair Value Disclosure [Member] | Commercial [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans	10,524,627	10,437,016
Estimate of Fair Value, Fair Value Disclosure [Member] | Commercial Real Estate [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans	3,428,733	3,850,981
Estimate of Fair Value, Fair Value Disclosure [Member] | Residential Mortgage [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans	1,977,721	2,025,159
Estimate of Fair Value, Fair Value Disclosure [Member] | Personal [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans	956,706	864,904
Estimate of Fair Value, Fair Value Disclosure [Member] | U.S. government agency debentures [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Trading securities	21,196	6,234
Estimate of Fair Value, Fair Value Disclosure [Member] | U.S. government agency residential mortgage-backed securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Trading securities	392,673	310,067
Investment securities	16,242	21,473
Available for sale securities	5,309,152	5,460,386
Fair value option securities	755,054	77,046
Estimate of Fair Value, Fair Value Disclosure [Member] | Municipal and other tax-exempt securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Trading securities	13,559	14,427
Investment securities	230,349	321,225
Available for sale securities	27,080	40,993
Estimate of Fair Value, Fair Value Disclosure [Member] | Asset-backed securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Trading securities	23,885	0
Estimate of Fair Value, Fair Value Disclosure [Member] | Other trading securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Trading securities	11,363	6,900
Estimate of Fair Value, Fair Value Disclosure [Member] | U.S. Treasury securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale securities	1,000	999
Estimate of Fair Value, Fair Value Disclosure [Member] | Privately issued residential mortgage-backed securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale securities	93,221	115,535
Estimate of Fair Value, Fair Value Disclosure [Member] | Commercial mortgage-backed securities guaranteed by U.S. government agencies [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale securities	2,834,961	3,017,933
Estimate of Fair Value, Fair Value Disclosure [Member] | Other debt securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investment securities	233,444	222,795
Available for sale securities	25,481	4,152
Estimate of Fair Value, Fair Value Disclosure [Member] | Perpetual preferred stock [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale securities	15,767	18,474
Estimate of Fair Value, Fair Value Disclosure [Member] | Equity securities and mutual funds [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale securities	14,916	18,357
Fair Value, Inputs, Level 1 [Member] | Estimate of Fair Value, Fair Value Disclosure [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and due from banks	602,510	620,846
Interest-bearing cash and cash equivalents	1,714,544	1,916,651
Trading securities	0	0
Investment securities	0	0
Available for sale securities	1,000	4,494
Residential mortgage loans held for sale	0	0
Loans	0	0
Allowance for loan losses	0	0
Loans, net of allowance	0	0
Mortgage servicing rights	0	0
Derivative contracts, net of cash margin, Assets, Fair Value	8,179	7,541
Deposits with no stated maturity	0	0
Time deposits	0	0
Other borrowed funds	0	0
Subordinated debentures	0	0
Derivative contracts, net of cash margin, Liabilities, Fair Value	0	6,972
Fair Value, Inputs, Level 1 [Member] | Estimate of Fair Value, Fair Value Disclosure [Member] | Commercial [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans	0	0
Fair Value, Inputs, Level 1 [Member] | Estimate of Fair Value, Fair Value Disclosure [Member] | Commercial Real Estate [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans	0	0
Fair Value, Inputs, Level 1 [Member] | Estimate of Fair Value, Fair Value Disclosure [Member] | Residential Mortgage [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans	0	0
Fair Value, Inputs, Level 1 [Member] | Estimate of Fair Value, Fair Value Disclosure [Member] | Personal [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans	0	0
Fair Value, Inputs, Level 1 [Member] | Estimate of Fair Value, Fair Value Disclosure [Member] | U.S. government agency debentures [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Trading securities	0	0
Fair Value, Inputs, Level 1 [Member] | Estimate of Fair Value, Fair Value Disclosure [Member] | U.S. government agency residential mortgage-backed securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Trading securities	0	0
Investment securities	0	0
Available for sale securities	0	0
Fair value option securities	0	0
Fair Value, Inputs, Level 1 [Member] | Estimate of Fair Value, Fair Value Disclosure [Member] | Municipal and other tax-exempt securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Trading securities	0	0
Investment securities	0	0
Available for sale securities	0	0
Fair Value, Inputs, Level 1 [Member] | Estimate of Fair Value, Fair Value Disclosure [Member] | Asset-backed securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Trading securities	0	0
Fair Value, Inputs, Level 1 [Member] | Estimate of Fair Value, Fair Value Disclosure [Member] | Other trading securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Trading securities	0	0
Fair Value, Inputs, Level 1 [Member] | Estimate of Fair Value, Fair Value Disclosure [Member] | U.S. Treasury securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale securities	1,000	999
Fair Value, Inputs, Level 1 [Member] | Estimate of Fair Value, Fair Value Disclosure [Member] | Privately issued residential mortgage-backed securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale securities	0	0
Fair Value, Inputs, Level 1 [Member] | Estimate of Fair Value, Fair Value Disclosure [Member] | Commercial mortgage-backed securities guaranteed by U.S. government agencies [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale securities	0	0
Fair Value, Inputs, Level 1 [Member] | Estimate of Fair Value, Fair Value Disclosure [Member] | Other debt securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investment securities	0	0
Available for sale securities	0	0
Fair Value, Inputs, Level 1 [Member] | Estimate of Fair Value, Fair Value Disclosure [Member] | Perpetual preferred stock [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale securities	0	0
Fair Value, Inputs, Level 1 [Member] | Estimate of Fair Value, Fair Value Disclosure [Member] | Equity securities and mutual funds [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale securities	0	3,495
Fair Value, Inputs, Level 2 [Member] | Estimate of Fair Value, Fair Value Disclosure [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and due from banks	0	0
Interest-bearing cash and cash equivalents	0	0
Trading securities	438,791	337,628
Investment securities	480,035	565,493
Available for sale securities	8,315,304	8,662,394
Residential mortgage loans held for sale	208,946	290,280
Loans	0	0
Allowance for loan losses	0	0
Loans, net of allowance	0	0
Mortgage servicing rights	0	0
Derivative contracts, net of cash margin, Assets, Fair Value	212,323	682,331
Deposits with no stated maturity	0	0
Time deposits	0	0
Other borrowed funds	0	0
Subordinated debentures	148,207	128,903
Derivative contracts, net of cash margin, Liabilities, Fair Value	171,963	657,559
Fair Value, Inputs, Level 2 [Member] | Estimate of Fair Value, Fair Value Disclosure [Member] | Commercial [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans	0	0
Fair Value, Inputs, Level 2 [Member] | Estimate of Fair Value, Fair Value Disclosure [Member] | Commercial Real Estate [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans	0	0
Fair Value, Inputs, Level 2 [Member] | Estimate of Fair Value, Fair Value Disclosure [Member] | Residential Mortgage [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans	0	0
Fair Value, Inputs, Level 2 [Member] | Estimate of Fair Value, Fair Value Disclosure [Member] | Personal [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans	0	0
Fair Value, Inputs, Level 2 [Member] | Estimate of Fair Value, Fair Value Disclosure [Member] | U.S. government agency debentures [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Trading securities	21,196	6,234
Fair Value, Inputs, Level 2 [Member] | Estimate of Fair Value, Fair Value Disclosure [Member] | U.S. government agency residential mortgage-backed securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Trading securities	392,673	310,067
Investment securities	16,242	21,473
Available for sale securities	5,309,152	5,460,386
Fair value option securities	755,054	77,046
Fair Value, Inputs, Level 2 [Member] | Estimate of Fair Value, Fair Value Disclosure [Member] | Municipal and other tax-exempt securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Trading securities	13,559	14,427
Investment securities	230,349	321,225
Available for sale securities	22,278	35,204
Fair Value, Inputs, Level 2 [Member] | Estimate of Fair Value, Fair Value Disclosure [Member] | Asset-backed securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Trading securities	23,885	0
Fair Value, Inputs, Level 2 [Member] | Estimate of Fair Value, Fair Value Disclosure [Member] | Other trading securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Trading securities	11,363	6,900
Fair Value, Inputs, Level 2 [Member] | Estimate of Fair Value, Fair Value Disclosure [Member] | U.S. Treasury securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale securities	0	0
Fair Value, Inputs, Level 2 [Member] | Estimate of Fair Value, Fair Value Disclosure [Member] | Privately issued residential mortgage-backed securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale securities	93,221	115,535
Fair Value, Inputs, Level 2 [Member] | Estimate of Fair Value, Fair Value Disclosure [Member] | Commercial mortgage-backed securities guaranteed by U.S. government agencies [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale securities	2,834,961	3,017,933
Fair Value, Inputs, Level 2 [Member] | Estimate of Fair Value, Fair Value Disclosure [Member] | Other debt securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investment securities	233,444	222,795
Available for sale securities	25,009	0
Fair Value, Inputs, Level 2 [Member] | Estimate of Fair Value, Fair Value Disclosure [Member] | Perpetual preferred stock [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale securities	15,767	18,474
Fair Value, Inputs, Level 2 [Member] | Estimate of Fair Value, Fair Value Disclosure [Member] | Equity securities and mutual funds [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale securities	14,916	14,862
Fair Value, Inputs, Level 3 [Member] | Estimate of Fair Value, Fair Value Disclosure [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and due from banks	0	0
Interest-bearing cash and cash equivalents	0	0
Trading securities	0	0
Investment securities	0	0
Available for sale securities	5,274	9,941
Residential mortgage loans held for sale	12,432	11,617
Loans	16,887,787	17,178,060
Allowance for loan losses	0	0
Loans, net of allowance	16,887,787	17,178,060
Mortgage servicing rights	252,867	247,073
Derivative contracts, net of cash margin, Assets, Fair Value	0	0
Deposits with no stated maturity	19,962,889	20,526,295
Time deposits	2,064,558	2,218,303
Other borrowed funds	5,703,121	5,556,327
Subordinated debentures	0	0
Derivative contracts, net of cash margin, Liabilities, Fair Value	0	0
Fair Value, Inputs, Level 3 [Member] | Estimate of Fair Value, Fair Value Disclosure [Member] | Commercial [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans	10,524,627	10,437,016
Fair Value, Inputs, Level 3 [Member] | Estimate of Fair Value, Fair Value Disclosure [Member] | Commercial Real Estate [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans	3,428,733	3,850,981
Fair Value, Inputs, Level 3 [Member] | Estimate of Fair Value, Fair Value Disclosure [Member] | Residential Mortgage [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans	1,977,721	2,025,159
Fair Value, Inputs, Level 3 [Member] | Estimate of Fair Value, Fair Value Disclosure [Member] | Personal [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans	956,706	864,904
Fair Value, Inputs, Level 3 [Member] | Estimate of Fair Value, Fair Value Disclosure [Member] | U.S. government agency debentures [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Trading securities	0	0
Fair Value, Inputs, Level 3 [Member] | Estimate of Fair Value, Fair Value Disclosure [Member] | U.S. government agency residential mortgage-backed securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Trading securities	0	0
Investment securities	0	0
Available for sale securities	0	0
Fair value option securities	0	0
Fair Value, Inputs, Level 3 [Member] | Estimate of Fair Value, Fair Value Disclosure [Member] | Municipal and other tax-exempt securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Trading securities	0	0
Investment securities	0	0
Available for sale securities	4,802	5,789
Fair Value, Inputs, Level 3 [Member] | Estimate of Fair Value, Fair Value Disclosure [Member] | Asset-backed securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Trading securities	0	0
Fair Value, Inputs, Level 3 [Member] | Estimate of Fair Value, Fair Value Disclosure [Member] | Other trading securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Trading securities	0	0
Fair Value, Inputs, Level 3 [Member] | Estimate of Fair Value, Fair Value Disclosure [Member] | U.S. Treasury securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale securities	0	0
Fair Value, Inputs, Level 3 [Member] | Estimate of Fair Value, Fair Value Disclosure [Member] | Privately issued residential mortgage-backed securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale securities	0	0
Fair Value, Inputs, Level 3 [Member] | Estimate of Fair Value, Fair Value Disclosure [Member] | Commercial mortgage-backed securities guaranteed by U.S. government agencies [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale securities	0	0
Fair Value, Inputs, Level 3 [Member] | Estimate of Fair Value, Fair Value Disclosure [Member] | Other debt securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investment securities	0	0
Available for sale securities	472	4,152
Fair Value, Inputs, Level 3 [Member] | Estimate of Fair Value, Fair Value Disclosure [Member] | Perpetual preferred stock [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale securities	0	0
Fair Value, Inputs, Level 3 [Member] | Estimate of Fair Value, Fair Value Disclosure [Member] | Equity securities and mutual funds [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale securities	$ 0	$ 0

Fair Value Measurements Fair 94

Fair Value Measurements Fair Value Measurements, Financial Instruments, Quantitative Information (Details)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Time Deposits [Member]
Fair Value Inputs, Financial Instruments, Quantitative Information [Line Items]
Contractual Yield, Minimum	0.03%	0.02%
Contractual Yield, Maximum	9.64%	9.65%
Repricing (in years)	1 year 332 days	1 year 350 days
Discount Rate, Minimum	2.18%	1.57%
Discount Rate, Maximum	2.36%	2.00%
Other borrowings [Member]
Fair Value Inputs, Financial Instruments, Quantitative Information [Line Items]
Contractual Yield, Minimum	0.25%	0.25%
Contractual Yield, Maximum	3.49%	3.50%
Repricing (in years)	1 day	1 day
Discount Rate, Minimum	1.33%	0.55%
Discount Rate, Maximum	4.04%	3.22%
Subordinated debentures [Member]
Fair Value Inputs, Financial Instruments, Quantitative Information [Line Items]
Contractual Yield, Minimum	5.38%	5.38%
Contractual Yield, Maximum	5.38%	5.38%
Repricing (in years)	16 years 288 days	16 years 314 days
Discount Rate, Minimum	4.61%	6.11%
Discount Rate, Maximum	4.61%	6.11%
Commercial [Member] | Loans [Member]
Fair Value Inputs, Financial Instruments, Quantitative Information [Line Items]
Contractual Yield, Minimum	0.38%	0.38%
Contractual Yield, Maximum	30.00%	30.00%
Repricing (in years)	234 days	256 days
Discount Rate, Minimum	0.77%	0.64%
Discount Rate, Maximum	4.67%	4.60%
Commercial Real Estate [Member] | Loans [Member]
Fair Value Inputs, Financial Instruments, Quantitative Information [Line Items]
Contractual Yield, Minimum	0.38%	0.38%
Contractual Yield, Maximum	18.00%	18.00%
Repricing (in years)	292 days	259 days
Discount Rate, Minimum	1.04%	0.94%
Discount Rate, Maximum	4.41%	4.27%
Residential Mortgage [Member] | Loans [Member]
Fair Value Inputs, Financial Instruments, Quantitative Information [Line Items]
Contractual Yield, Minimum	1.74%	1.74%
Contractual Yield, Maximum	18.00%	18.00%
Repricing (in years)	2 years 99 days	2 years 99 days
Discount Rate, Minimum	2.11%	1.71%
Discount Rate, Maximum	4.09%	4.26%
Personal [Member] | Loans [Member]
Fair Value Inputs, Financial Instruments, Quantitative Information [Line Items]
Contractual Yield, Minimum	1.18%	0.25%
Contractual Yield, Maximum	21.00%	21.00%
Repricing (in years)	84 days	146 days
Discount Rate, Minimum	0.56%	1.03%
Discount Rate, Maximum	4.81%	4.59%

Parent Company Only Financial95

Parent Company Only Financial Statements Parent Company Only Financial Statements, Condensed Balance Sheet Statement (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Assets [Abstract]
Cash and cash equivalents	$ 2,317,054	$ 2,537,497	$ 2,643,599	$ 2,475,842
Available for sale securities	8,321,578	8,676,829
Other assets	359,092	353,017
Total assets	32,272,160	32,772,281
Liabilities [Abstract]
Other liabilities	349,928	182,784
Subordinated debentures	144,677	144,640
Total liabilities	28,753,826	29,465,924
Shareholders' equity: [Abstract]
Common stock	4	4
Capital surplus	1,035,895	1,006,535
Retained earnings	3,048,487	2,823,334
Treasury stock	(552,845)	(544,052)
Accumulated other comprehensive loss	(36,174)	(10,967)	21,587	56,673
Total shareholders’ equity	3,495,367	3,274,854
Total liabilities and shareholders’ equity	32,272,160	32,772,281
Parent Company [Member]
Assets [Abstract]
Cash and cash equivalents	205,876	163,418	$ 282,169	$ 510,668
Available for sale securities	16,185	19,234
Investment in bank subsidiaries	3,255,912	3,067,595
Investment in non-bank subsidiaries	170,966	177,068
Other assets	4,065	4,865
Total assets	3,653,004	3,432,180
Liabilities [Abstract]
Other liabilities	12,960	5,469
Other borrowings – Trust preferred debt	0	7,217
Subordinated debentures	144,677	144,640
Total liabilities	157,637	157,326
Shareholders' equity: [Abstract]
Common stock	4	4
Capital surplus	1,035,895	1,006,535
Retained earnings	3,048,487	2,823,334
Treasury stock	(552,845)	(544,052)
Accumulated other comprehensive loss	(36,174)	(10,967)
Total shareholders’ equity	3,495,367	3,274,854
Total liabilities and shareholders’ equity	$ 3,653,004	$ 3,432,180

Parent Company Only Financial96

Parent Company Only Financial Statements Parent Company Only Financial Statements, Condensed Income Statements (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Condensed Income Statements, Captions [Line Items]
Other revenue	$ 52,168	$ 51,029	$ 49,883
Interest expense	131,050	81,889	63,474
Other operating expense	1,025,517	1,017,590	896,191
Federal and state income taxes	182,593	106,377	139,384
Net income attributable to BOK Financial Corp. shareholders	334,644	232,668	288,565
Parent Company [Member]
Condensed Income Statements, Captions [Line Items]
Dividends, interest and fees received from bank subsidiaries	150,149	15,237	150,308
Dividends, interest and fees received from non-bank subsidiaries	17,500	25,923	0
Other revenue	936	1,612	1,279
Total revenue	168,585	42,772	151,587
Interest expense	8,239	4,182	131
Other operating expense	2,014	1,978	2,242
Total expense	10,253	6,160	2,373
Income before taxes and equity in undistributed income of subsidiaries	158,332	36,612	149,214
Federal and state income taxes	(4,305)	(1,920)	(375)
Income before equity in undistributed income of subsidiaries	162,637	38,532	149,589
Equity in undistributed income of bank subsidiaries	181,552	216,120	134,045
Equity in undistributed income of non-bank subsidiaries	(9,545)	(21,984)	4,931
Net income attributable to BOK Financial Corp. shareholders	$ 334,644	$ 232,668	$ 288,565

Parent Company Only Financial97

Parent Company Only Financial Statements Parent Company Only Financial Statements, Condensed Cash Flow Statement (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash Flows From Operating Activities: [Abstract]
Net income	$ 335,685	$ 232,281	$ 292,259
Adjustments to reconcile net income to net cash provided by operating activities: [Abstract]
Change in other assets	(5,506)	(49,565)	(29,548)
Change in other liabilities	182,184	(11,413)	15,756
Net cash provided by operating activities	214,931	(91,949)	295,935
Cash Flows From Investing Activities: [Abstract]
Proceeds from sales of available for sale securities	1,309,215	899,381	1,600,380
Acquisitions, net of cash acquired	0	56,017	(18,098)
Net cash used in investing activities	739,556	(286,007)	(2,001,304)
Cash Flows From Financing Activities: [Abstract]
Net change in other borrowed funds	(10,909)	(606,476)	2,547,688
Issuance of subordinated debentures, net of issuance costs	0	144,615	0
Issuance of common and treasury stock, net	4,368	12,455	6,711
Dividends paid	(116,041)	(113,455)	(115,281)
Repurchase of common stock	(7,403)	(66,792)	(229,540)
Net cash used in financing activities	(1,174,930)	271,854	1,873,126
Net increase (decrease) in cash and cash equivalents	(220,443)	(106,102)	167,757
Cash and cash equivalents at beginning of period	2,537,497	2,643,599	2,475,842
Cash and cash equivalents at end of period	2,317,054	2,537,497	2,643,599
Cash paid for interest	127,513	82,876	66,091
Parent Company [Member]
Cash Flows From Operating Activities: [Abstract]
Net income	334,644	232,668	288,565
Adjustments to reconcile net income to net cash provided by operating activities: [Abstract]
Equity in undistributed income of bank subsidiaries	(181,552)	(216,120)	(134,045)
Equity in undistributed income of non-bank subsidiaries	9,545	21,984	(4,931)
Change in other assets	12	(2,933)	49
Change in other liabilities	7,457	(1,285)	(2,818)
Net cash provided by operating activities	170,106	34,314	146,820
Cash Flows From Investing Activities: [Abstract]
Proceeds from sales of available for sale securities	3,000	1,632	4,760
Investment in subsidiaries	(4,355)	(26,000)	(41,969)
Acquisitions, net of cash acquired	0	(105,520)	0
Net cash used in investing activities	(1,355)	(129,888)	(37,209)
Cash Flows From Financing Activities: [Abstract]
Net change in other borrowed funds	(7,217)	0	0
Issuance of subordinated debentures, net of issuance costs	0	144,615	0
Issuance of common and treasury stock, net	4,368	12,455	6,711
Dividends paid	(116,041)	(113,455)	(115,281)
Repurchase of common stock	(7,403)	(66,792)	(229,540)
Net cash used in financing activities	(126,293)	(23,177)	(338,110)
Net increase (decrease) in cash and cash equivalents	42,458	(118,751)	(228,499)
Cash and cash equivalents at beginning of period	163,418	282,169	510,668
Cash and cash equivalents at end of period	205,876	163,418	282,169
Cash paid for interest	$ 6,211	$ 4,127	$ 131