First Interstate BancSystem (FIBK) 10-K 1 Mar 16 2015 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2015	Jan. 31, 2016	Jun. 30, 2015
Entity Registrant Name	FIRST INTERSTATE BANCSYSTEM INC
Entity Central Index Key	860,413
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Document Type	10-K
Document Period End Date	Dec. 31, 2015
Document Fiscal Year Focus	2,015
Document Fiscal Period Focus	FY
Amendment Flag	false
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Public Float			$ 668,057,399
Class A Common Stock
Entity Common Stock, Shares Outstanding		21,511,142
Class B Common Stock
Entity Common Stock, Shares Outstanding		23,729,282

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Assets
Cash and due from banks	$ 132,595	$ 147,894
Federal funds sold	563	543
Interest bearing deposits in banks	647,299	650,233
Total cash and cash equivalents	780,457	798,670
Investment securities:
Available-for-sale	1,456,840	1,711,924
Held-to-maturity (estimated fair values of $607,550 and $584,533 at December 31, 2015 and 2014, respectively)	600,665	575,186
Total investment securities	2,057,505	2,287,110
Loans held for investment	5,193,321	4,856,615
Mortgage loans held for sale	52,875	40,828
Total loans	5,246,196	4,897,443
Less allowance for loan losses	76,817	74,200
Net loans	5,169,379	4,823,243
Premises and equipment, net of accumulated depreciation	190,812	195,212
Goodwill	204,523	205,574
Company-owned life insurance	187,253	153,821
Other real estate owned (“OREO”)	6,254	13,554
Accrued interest receivable	27,729	27,063
Mortgage servicing rights, net of accumulated amortization and impairment reserve	15,621	14,038
Deferred tax asset, net	0	4,874
Core deposit intangibles, net of accumulated amortization	10,589	13,282
Other assets	78,074	73,495
Total assets	8,728,196	8,609,936
Deposits:
Non-interest bearing	1,823,716	1,791,364
Interest bearing	5,265,221	5,214,848
Total deposits	7,088,937	7,006,212
Securities sold under repurchase agreements	510,635	502,250
Accounts payable and accrued expenses	53,042	66,164
Accrued interest payable	4,960	5,833
Deferred tax liability, net	9,765	0
Long-term debt	27,885	38,067
Other borrowed funds	2	9
Subordinated debentures held by subsidiary trusts	82,477	82,477
Total liabilities	7,777,703	7,701,012
Stockholders’ equity:
Nonvoting noncumulative preferred stock without par value; authorized 100,000 shares; no shares issued or outstanding as of December 31, 2015 and 2014	0	0
Common stock	311,720	323,596
Retained earnings	638,367	587,862
Accumulated other comprehensive gain (loss), net	406	(2,534)
Total stockholders’ equity	950,493	908,924
Total liabilities and stockholders’ equity	$ 8,728,196	$ 8,609,936

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Assets:
Held-to-Maturity Estimated Fair Value	$ 607,550	$ 584,533
Stockholders' Equity:
Nonvoting, noncumulative preferred stock, par value	$ 0	$ 0
Nonvoting, noncumulative preferred stock, shares authorized	100,000	100,000
Nonvoting, noncumulative preferred stock, shares issued	0	0
Nonvoting, noncumulative preferred stock, shares outstanding	0	0

Consolidated Statements of Inco

Consolidated Statements of Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Interest income:
Interest and fees on loans	$ 246,015	$ 231,469	$ 220,687
Interest and dividends on investment securities:
Taxable	30,861	29,900	31,237
Exempt from federal taxes	3,998	4,357	4,728
Interest on deposits in banks	1,537	1,334	992
Interest on federal funds sold	12	7	18
Total interest income	282,423	267,067	257,662
Interest expense:
Interest on deposits	13,107	13,779	15,800
Interest on securities sold under repurchase agreements	231	237	294
Interest on long-term debt	2,300	2,016	1,936
Interest in preferred stock pending redemption	0	0	159
Interest on subordinated debentures held by subsidiary trusts	2,422	2,574	2,506
Total interest expense	18,060	18,606	20,695
Net interest income	264,363	248,461	236,967
Provision for loan losses	6,822	(6,622)	(6,125)
Net interest income after provision for loan losses	257,541	255,083	243,092
Non-interest income:
Other service charges, commissions and fees	43,154	40,742	35,977
Income from the origination and sale of loans	29,973	23,940	34,254
Wealth management revenues	19,907	18,996	17,085
Service charges on deposit accounts	17,031	16,567	16,837
Investment securities gains, net	137	61	1
Other income	10,727	11,095	7,525
Total non-interest income	120,929	111,401	111,679
Non-interest expense:
Salaries and wages	101,451	96,513	94,002
Employee benefits	30,738	30,130	30,338
Occupancy, net	17,879	17,796	16,587
Furniture and equipment	15,524	13,816	12,554
Outsourced technology services	10,124	9,423	9,029
FDIC insurance premiums	4,858	4,608	5,057
Professional fees	6,458	4,882	4,773
OREO expense, net of income	(1,475)	(272)	2,291
Mortgage servicing rights amortization	2,434	2,361	2,787
Mortgage servicing rights impairment recovery	(97)	(136)	(99)
Core deposit intangibles amortization	3,388	2,251	1,418
Other expenses	50,936	47,480	43,332
Loss Contingency Expense	5,000	4,000	0
Acquisition Expense	795	4,017	0
Total non-interest expense	248,013	236,869	222,069
Income before income tax expense	130,457	129,615	132,702
Income tax expense	43,662	45,214	46,566
Net income	$ 86,795	$ 84,401	$ 86,136
Basic earnings per common share	$ 1.92	$ 1.89	$ 1.98
Diluted earnings per common share	$ 1.90	$ 1.87	$ 1.96

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Consolidated Statements of Comprehensive Income [Abstract]
Net income	$ 86,795	$ 84,401	$ 86,136
Investment securities available-for-sale:
Change in net unrealized gains (losses) during the period	5,863	21,147	(52,949)
Reclassification adjustment for net gains included in income	(137)	(61)	(1)
Change in unamortized loss on available-for-sale investment securities transferred into held-to-maturity	(1,101)	(548)	0
Unrealized Gain (Loss) on Derivatives	165	0	0
Defined benefit post-retirement benefits plans:
Change in net actuarial loss	58	1,731	137
Other comprehensive income (loss), before tax	4,848	22,269	(52,813)
Deferred tax benefit (expense) related to other comprehensive income (loss)	(1,908)	(8,762)	20,781
Other comprehensive income (loss), net of tax	2,940	13,507	(32,032)
Total comprehensive income	$ 89,735	$ 97,908	$ 54,104

Consolidated Statements of Stoc

Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Retained Earnings	Accumulated Other Comprehensive Income (Loss)
Beginning Balance at Dec. 31, 2012	$ 751,186	$ 271,335	$ 463,860	$ 15,991
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	86,136	0	86,136	0
Other comprehensive loss, net of tax	(32,032)	0	0	(32,032)
Common stock transactions:
Common shares purchased and retired	448	(448)	0	0
Common shares issued	543	543	0	0
Non-vested common shares issued	0	0	0	0
Non-vested common shares forfeited or canceled	0	0	0	0
Stock options exercised, net of shares tendered in payment of option price and income tax withholding amounts	9,271	9,271	0	0
Tax benefit of stock-based compensation	1,898	1,898	0	0
Stock-based compensation expense	2,936	2,936	0	0
Cash dividends declared:
Common (per share)	(17,909)	0	(17,909)	0
Ending Balance at Dec. 31, 2013	801,581	285,535	532,087	(16,041)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	84,401	0	84,401	0
Other comprehensive loss, net of tax	13,507	0	0	13,507
Common stock transactions:
Common shares purchased and retired	(9,739)	(9,739)	0	0
Common shares issued	35,674	35,674	0	0
Non-vested common shares issued	0	0	0	0
Non-vested common shares forfeited or canceled	0	0	0	0
Stock options exercised, net of shares tendered in payment of option price and income tax withholding amounts	6,299	6,299	0	0
Tax benefit of stock-based compensation	2,193	2,193	0	0
Stock-based compensation expense	3,634	3,634	0	0
Cash dividends declared:
Common (per share)	(28,626)	0	(28,626)	0
Ending Balance at Dec. 31, 2014	908,924	323,596	587,862	(2,534)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	86,795	0	86,795	0
Other comprehensive loss, net of tax	2,940	0	0	2,940
Common stock transactions:
Common shares purchased and retired	(20,647)	(20,647)	0	0
Common shares issued	0	0	0	0
Non-vested common shares issued	0	0	0	0
Non-vested common shares forfeited or canceled	0	0	0	0
Stock options exercised, net of shares tendered in payment of option price and income tax withholding amounts	3,369	3,369	0	0
Tax benefit of stock-based compensation	1,443	1,443	0	0
Stock-based compensation expense	3,959	$ 3,959	0	0
Cash dividends declared:
Common (per share)	(36,290)		(36,290)	0
Ending Balance at Dec. 31, 2015	$ 950,493	$ 311,720	$ 638,367	$ 406

Consolidated Statements of Sto7

Consolidated Statements of Stockholders' Equity (Parenthetical) - $ / shares	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Common stock transactions:
Stock options exercised	350,438
Common stock
Common stock transactions:
Common shares purchased and retired	793,077	388,101	25,677
Common shares issued	21,414	1,402,811	26,096
Non-vested common shares issued	169,577	148,278	120,873
Non-vested common shares forfeited	19,184	29,261	30,648
Stock options exercised	350,438	499,625	774,096
Shares tendered in payment of option price and income tax withholding amounts	89,358	239,665	392,411
Preferred Stock Including Additional Paid in Capital [Member]
Common stock transactions:
Stock Redeemed or Called During Period, Shares	0	5,000	0
Retained Earnings
Cash dividends declared:
Common (in dollars per share)	$ 0.80	$ 0.64	$ 0.41
Preferred (in dollars per share)	0.00%	0.00%	0.00%

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Cash flows from operating activities:
Net income	$ 86,795	$ 84,401	$ 86,136
Adjustments to reconcile net income from operations to net cash provided by operating activities:
Provision for loan losses	(6,822)	6,622	6,125
Net gain on disposal of property and equipment	(731)	(1,256)	(217)
Depreciation and amortization	18,313	16,855	16,245
Net premium amortization on investment securities	14,880	14,690	14,655
Net gain on investment securities transactions	(137)	(61)	(1)
Net gain on sale of mortgage loans held for sale	(21,748)	(17,475)	(24,482)
Net gain on sale of OREO	(2,991)	(1,849)	(3,232)
Write-down of OREO and other assets pending disposal	1,013	326	3,512
Mortgage servicing rights impairment recovery	(97)	(136)	(99)
Deferred income tax expense	12,449	5,345	11,276
Net increase in cash surrender value of company-owned life insurance policies	(3,432)	(3,600)	(446)
Stock-based compensation expense	3,959	3,634	2,936
Tax benefits from stock-based compensation	1,443	2,193	1,898
Excess tax benefits from stock-based compensation	(1,184)	(2,205)	(2,031)
Originations of loans held for sale	(1,148,098)	(903,373)	(1,557,288)
Proceeds from Sale of Mortgage Loans Held-for-sale	1,164,804	923,350	1,603,770
Changes in operating assets and liabilities:
Decrease (increase) in accrued interest receivable	(101)	470	2,419
Decrease (increase) in other assets	(3,622)	(6,956)	3,440
Increase (decrease) in accrued interest payable	(1,006)	286	(1,539)
Increase (decrease) in accounts payable and accrued expenses	(11,931)	13,991	(602)
Net cash provided by operating activities	115,400	122,008	150,225
Purchases of investment securities:
Held-to-maturity	(45,179)	(21,627)	(16,370)
Available-for-sale	(474,846)	(664,821)	(741,579)
Proceeds from maturities, paydowns, calls and sales of investment securities:
Held-to-maturity	118,406	47,784	19,465
Available-for-sale	648,683	613,930	722,447
Payments to Acquire Life Insurance Policies	(30,000)	(15,000)	(45,000)
Proceeds from sales of mortgage servicing rights	0	266	470
Extensions of credit to customers, net of repayments	(327,878)	(216,730)	(178,580)
Recoveries of loans charged-off	7,432	9,478	11,466
Proceeds from sales of OREO	15,644	12,381	28,397
Payments to Acquire Businesses, Net of Cash Acquired	(1,636)	35,556	0
Capital expenditures, net of proceeds from sales	(5,965)	2,941	(5,653)
Net cash used in investing activities	(95,339)	(195,842)	(204,937)
Cash flows from financing activities:
Net increase (decrease) in deposits	19,160	357,083	(106,661)
Net increase (decrease) in repurchase agreements	6,385	43,892	(48,348)
Net decrease in short-term borrowings	(7)	(12,720)	(29)
Proceeds from Issuance of Unsecured Debt	5,103	68	0
Repayments of long-term debt	(16,538)	(48)	(243)
Write off of Deferred Debt Issuance Cost	7	0	0
Payments for Repurchase of Preferred Stock and Preference Stock	0	0	(50,000)
Repayment of junior subordinated debentures held by subsidiary trusts	0	(20,439)	0
Proceeds from issuance of common stock	3,369	6,299	9,814
Payments of Stock Issuance Costs	0	298	0
Excess tax benefits from stock-based compensation	1,184	2,205	2,031
Purchase and retirement of common stock	(20,647)	(9,739)	(448)
Dividends paid to common stockholders	(36,290)	(28,626)	(17,909)
Net cash used in financing activities	(38,274)	337,677	(211,793)
Net increase (decrease) in cash and cash equivalents	(18,213)	263,843	(266,505)
Cash and cash equivalents at beginning of year	798,670	534,827	801,332
Cash and cash equivalents at end of year	780,457	798,670	534,827
Supplemental disclosures of cash flow information:
Cash paid during the year for income taxes	27,335	26,650	39,879
Cash paid during the year for interest expense	$ 18,933	$ 17,736	$ 22,234

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2015
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Business . First Interstate BancSystem, Inc. (the “Parent Company” and collectively with its subsidiaries, the “Company”) is a financial and bank holding company that, through the branch offices of its bank subsidiary, provides a comprehensive range of banking products and services to individuals, businesses, municipalities and other entities throughout Montana, Wyoming and South Dakota. In addition to its primary emphasis on commercial and consumer banking services, the Company also offers trust, employee benefit, investment and insurance services through its bank subsidiary. The Company is subject to competition from other financial institutions and nonbank financial companies, and is also subject to the regulations of various government agencies and undergoes periodic examinations by those regulatory authorities. Basis of Presentation . The Company’s consolidated financial statements include the accounts of the Parent Company and its operating subsidiaries. As of December 31, 2015 , the Company had one significant subsidiary, First Interstate Bank (“FIB”). All significant intercompany balances and transactions have been eliminated in consolidation. Certain reclassifications, none of which were material, have been made in the consolidated financial statements for 2014 and 2013 to conform to the 2015 presentation. These reclassifications did not change previously reported net income or stockholders’ equity. Equity Method Investments. The Company has investments in real estate joint ventures that are not consolidated because the Company does not own a majority voting interest, control the operations or receive a majority of the losses or earnings of the joint venture. These joint ventures are accounted for using the equity method of accounting whereby the Company initially records its investment at cost (or fair value at the date of acquisition) and then subsequently adjusts the carrying value for the Company’s proportionate share of distributions and earnings or losses of the joint ventures. Variable Interest Entities. The Company’s wholly-owned business trusts, FI Statutory Trust I (“Trust I”), FI Capital Trust II (“Trust II”), FI Statutory Trust III (“Trust III”), FI Capital Trust IV (“Trust IV”), FI Statutory Trust V (“Trust V”) and FI Statutory Trust VI (“Trust VI”) are variable interest entities for which the Company is not a primary beneficiary. Accordingly, the accounts of Trust I, Trust II, Trust III, Trust IV, Trust V and Trust VI are not included in the accompanying consolidated financial statements, and are instead accounted for using the equity method of accounting. The Company has equity investments in variable interest Certified Development Entities (“CDEs”) which have received allocations under the New Markets Tax Credits Program. The underlying activities of the CDEs are community development projects designed primarily to promote community welfare, such as economic rehabilitation and development of low-income areas by providing housing, services, or jobs for residents. The maximum exposure to loss in the CDEs is the amount of equity invested and credit extended by the Company. The Company has credit protection in the form of indemnification agreements, guarantees, and collateral arrangements. As the primary beneficiary of these variable interest entities, the Company’s consolidated financial statements include the assets, liabilities, and results of operations of the CDEs. The primary activities of the CDEs are recognized in interest and fees on loans, other non-interest income and long-term debt interest expense on the Company’s statements of operations. Related cash flows are recognized in loans originated, principal collected on loans and advances or repayments of long-term debt. Assets Held in Fiduciary or Agency Capacity. The Company holds certain trust assets in a fiduciary or agency capacity. The Company also purchases and sells federal funds as an agent. These and other assets held in an agency or fiduciary capacity are not assets of the Company and, accordingly, are not included in the accompanying consolidated financial statements. Use of Estimates. The preparation of consolidated financial statements in conformity with accounting principles generally accepted in the United States of America requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and the disclosure of contingent assets and liabilities at the date of the financial statements and income and expenses during the reporting period. Actual results could differ from those estimates. Material estimates that are particularly susceptible to change relate to the determination of the allowance for loan losses, the valuation of goodwill, fair valuations of investment securities and other financial instruments and the status of loss contingencies. Cash and Cash Equivalents . For purposes of reporting cash flows, cash and cash equivalents include cash on hand, amounts due from banks, federal funds sold for one day periods and interest bearing deposits in banks with original maturities of less than three months. As of December 31, 2015 and 2014 , the Company had cash of $636,345 and $631,562 , respectively, on deposit with the Federal Reserve Bank. In addition, the Company maintained compensating balances with the Federal Reserve Bank of approximately $10,031 and $7,507 as of December 31, 2015 and 2014 , respectively, to reduce service charges for check clearing services. Investment Securities . Investments in debt securities that the Company has the positive intent and ability to hold to maturity are classified as held-to-maturity and carried at amortized cost. Investments in debt securities that may be sold in response to or in anticipation of changes in interest rates and resulting prepayment risk, or other factors, and marketable equity securities are classified as available-for-sale and carried at fair value. The unrealized gains and losses on these securities are reported, net of applicable income taxes, as a separate component of stockholders’ equity and comprehensive income. Management determines the appropriate classification of securities at the time of purchase and at each reporting date management reassesses the appropriateness of the classification. The amortized cost of debt securities classified as held-to-maturity or available-for-sale is adjusted for accretion of discounts to maturity and amortization of premiums over the estimated average life of the security, or in the case of callable securities, through the first call date, using the effective yield method. Such amortization and accretion is included in interest income. Realized gains and losses are included in investment securities gains (losses). Declines in the fair value of securities below their cost that are judged to be other-than-temporary are included in other expenses if the decline is related to credit losses. Other-than-temporary impairment losses related to other factors are recognized in other comprehensive income, net of income taxes. In estimating other-than-temporary impairment losses, the Company considers, among other things, the length of time and the extent to which the fair value has been less than cost, the financial condition and near-term prospects of the issuer and the intent and ability of the Company to retain its investment in the issuer for a period of time sufficient to allow for any anticipated recovery in fair value. The cost of securities sold is based on the specific identification method. Loans . Loans are reported at the principal amount outstanding. Interest income on loans is calculated using the simple interest method on the daily balance of the principal amount outstanding. Loan origination fees and certain direct origination costs are deferred, and the net amount is amortized as an adjustment of the related loan’s yield using a level yield method over the expected lives of the related loans. The accrual of interest on loans is discontinued when, in management’s opinion, the borrower may be unable to meet payment obligations as they become due or when a loan becomes contractually past due ninety days or more with respect to interest or principal, unless such past due loan is well secured and in the process of collection. When interest accrual is discontinued, all unpaid accrued interest is reversed against current period interest income. Interest income is subsequently recognized only to the extent cash payments are received in excess of principal due. Loans are returned to accrual status when all principal and interest amounts contractually due are brought current and when, in the opinion of management, the loans are estimated to be fully collectible as to both principal and interest. A loan is considered impaired when, based upon current information and events, it is probable that the Company will be unable to collect, on a timely basis, all amounts due according to the contractual terms of the loan’s original agreement. The amount of the impairment is measured using cash flows discounted at the loan’s effective interest rate, except when it is determined that the primary source of repayment for the loan is the operation or liquidation of the underlying collateral. In such cases, the current fair value of the collateral, reduced by anticipated selling costs, is used to measure impairment. The Company considers impaired loans to include all loans, except consumer loans, that are risk rated as doubtful or on which interest accrual has been discontinued or that have been renegotiated in a troubled debt restructuring. Interest payments received on impaired loans are applied based on whether they are on accrual or non-accrual status. Interest income recognized by the Company on impaired loans primarily relates to loans modified in troubled debt restructurings that remain on accrual status. Interest payments received on non-accrual impaired loans are applied to principal. Interest income is subsequently recognized only to the extent cash payments are received in excess of principal due. Loans acquired through the completion of a transfer, including loans acquired in business combinations, that have evidence of deterioration of credit quality since origination and for which it is probable, at acquisition, that the Company will be unable to collect all contractually required payments receivable are initially recorded at fair value (as determined by the present value of expected future cash flows) with no valuation allowance. The difference between the undiscounted cash flows expected at acquisition and the recorded fair value of the loan, or the “accretable yield,” is recognized as interest income on a level-yield method over the life of the loan. Contractually required payments for interest and principal that exceed the undiscounted cash flows expected at acquisition, or the “nonaccretable difference,” are not recognized as a yield adjustment, a loss accrual or a valuation allowance. Increases in expected cash flows subsequent to the initial investment are recognized prospectively through adjustment of the yield on the loan over its remaining life. Decreases in expected cash flows are recognized as impairment. Valuation allowances on these impaired loans reflect only losses incurred after the acquisition. A loan is considered a troubled debt restructuring when a borrower is experiencing financial difficulties that leads to a restructuring of the loan and the Company grants concessions to the borrower in the restructuring that it would not otherwise consider. These concessions may include rate reductions, principal forgiveness, extension of maturity date and other actions to minimize potential losses. Certain troubled debt restructurings are on non-accrual status at the time of restructuring and are returned to accrual status only after considering the borrower's sustained repayment performance in accordance with the restructuring agreement for a reasonable period of at least six months and management is reasonably assured of future performance. If the troubled debt restructuring meets these performance criteria and the interest rate granted at the modification is equal to or greater than the rate that the Company was willing to accept at the time of the restructuring for a new loan with comparable risk, then the loan will no longer be disclosed as a troubled debt restructuring although they continue to be individually evaluated for impairment and disclosed as impaired loans. Included in loans are certain residential mortgage loans originated for sale. These loans are carried at the lower of aggregate cost or estimated market value. Market value is estimated based on binding contracts or quotes or bids from third party investors. Residential mortgages held for sale were $52,875 and $40,828 as of December 31, 2015 and 2014 , respectively. Gains and losses on sales of mortgage loans are determined using the specific identification method and are included in income from the origination and sale of loans. As of December 31, 2015, the Company had no recorded investments in consumer mortgage loans secured by residential real estate for which formal foreclosure proceedings were in process. Allowance for Loan Losses . The allowance for loan losses is established through a provision for loan losses which is charged to expense. Loans, or portions thereof, are charged against the allowance for loan losses when management believes that the collectibility of the principal is unlikely or, with respect to consumer installment and credit card loans, according to established delinquency schedules. The allowance balance is an amount that management believes will be adequate to absorb known and inherent losses in the loan portfolio based upon quarterly analyses of the current risk characteristics of the loan portfolio, an assessment of individual problem loans and actual loss experience, industry concentrations and current economic factors and the estimated impact of current economic and environmental conditions on historical loss rates. Loans acquired in business combinations are recorded at their estimated fair values on the date of acquisition. Accordingly, no allowance for loan losses related to these loans is recorded at the date of transfer. An allowance for loan losses is recorded for credit deterioration occurring subsequent to the transfer date, if any. Goodwill . The excess purchase price over the fair value of net assets from acquisitions, or goodwill, is evaluated for impairment at least annually and on an interim basis if an event or circumstance indicates that it is likely impairment has occurred. Goodwill impairment is determined by comparing the fair value of a reporting unit to its carrying amount. In any given year the Company may elect to perform a qualitative assessment to determine whether it is more likely than not that the fair value of a reporting unit is in excess of its carrying value. If it is not more likely than not that the fair value of the reporting unit is in excess of the carrying value, or if the Company elects to bypass the qualitative assessment, a two-step quantitative impairment test is performed. In performing a quantitative test for impairment, the fair value of net assets is estimated based on analyses of the Company's market value, discounted cash flows and peer values. The determination of goodwill impairment is sensitive to market-based economics and other key assumptions used in determining or allocating fair value. Variability in the market and changes in assumptions or subjective measurements used to allocate fair value are reasonably possible and may have a material impact on our consolidated financial statements or results of operations. Core Deposit Intangibles. Core deposit intangibles represent the intangible value of depositor relationships resulting from deposit liabilities assumed and are amortized using an accelerated method based on the estimated weighted average useful lives of the related deposits. Accumulated core deposit intangibles amortization was $28,040 as of December 31, 2015 and $24,652 as of December 31, 2014 . Amortization expense related to core deposit intangibles recorded as of December 31, 2015 is expected to total $ 3,220 , $ 1,933 , $ 1,414 , $ 1,201 , $ 988 , and $ 1,833 in 2016 , 2017 , 2018 , 2019 , 2020 , and thereafter, respectively. Mortgage Servicing Rights . The Company recognizes the rights to service mortgage loans for others, whether acquired or internally originated. Mortgage servicing rights are initially recorded at fair value based on comparable market data and are amortized in proportion to and over the period of estimated net servicing income. Mortgage servicing rights are evaluated quarterly for impairment by discounting the expected future cash flows, taking into consideration the estimated level of prepayments based on current industry expectations and the predominant risk characteristics of the underlying loans including loan type, note rate and loan term. Impairment adjustments, if any, are recorded through a valuation allowance. Premises and Equipment . Buildings, furniture and equipment are stated at cost less accumulated depreciation. Depreciation expense is computed using straight-line methods over estimated useful lives of 5 to 45 years for buildings and improvements and 4 to 15 years for furniture and equipment. Leasehold improvements and assets acquired under capital lease are amortized over the shorter of their estimated useful lives or the terms of the related leases. Land is recorded at cost. Company-Owned Life Insurance . Key executive and group life insurance policies are recorded at their cash surrender value. Separate account group life insurance policies are subject to a stable value contract that offsets the impact of interest rate fluctuations on the market value of the policies and are recorded at the stabilized investment value. Increases in the cash surrender or stabilized investment value of insurance policies, as well as insurance proceeds received, are recorded as other non-interest income, and are not subject to income taxes. Deferred Compensation Plan. The Company has a deferred compensation plan for the benefit of certain highly compensated officers and directors of the Company. The plan allows for discretionary employer contributions in excess of tax limits applicable to the Company's 401(k) and profit sharing plans and the deferral of salary, short-term incentives or director fees subject to certain limitations. Deferred compensation plan assets and liabilities are included in the Company's consolidated balance sheets at fair value. Deferred compensation plan income or expense, consisting solely of net realized and unrealized holding gains and losses on deferred compensation plan assets, is recorded as other income in the Company’s consolidated statements of income. The corresponding net realized and unrealized holding gains and losses on deferred compensation plan liabilities is offset against employee benefits expense. As of December 31, 2015 and 2014, deferred compensation plan assets were $10,149 and $10,312, respectively. Corresponding deferred compensation plan liabilities were $10,149 and $10,136 as of December 31, 2015 and 2014, respectively. During 2015, net realized and unrealized holding losses on deferred compensation plan assets of $585 were included in other non-interest income and employee benefits expense in the Company's consolidated statements of income. During 2014, net realized and unrealized holding gains on deferred compensation plan assets of $434 were included in other non-interest income and employee benefits expense in the Company's consolidated statements of income. Impairment of Long-Lived Assets. Long-lived assets, including premises and equipment and certain identifiable intangibles, are reviewed for impairment whenever events or changes in circumstances indicate the carrying amount of an asset may not be recoverable. The amount of the impairment loss, if any, is based on the asset’s fair value. Impairment losses of $ 806 , $102 and $616 were recognized in other non-interest expense in 2015 , 2014 and 2013 , respectively. Other Real Estate Owned . Real estate acquired in satisfaction of loans is initially carried at current fair value less estimated selling costs. Any excess of loan carrying value over the fair value of the real estate acquired is recorded as a charge to the allowance for loan losses. Subsequent declines in fair value less estimated selling costs are included in OREO expense. Subsequent increases in fair value less estimated selling costs are recorded as a reduction in OREO expense to the extent of recognized losses. Operating expenses, net of related income, and gains or losses on sales are included in OREO expense. Write-downs of $207 , $224 and $3,512 were recorded in 2015 , 2014 and 2013 , respectively. The carrying value of foreclosed residential real estate properties included in other real estate owned was $1,686 as of December 31, 2015, and $2,644 as of December 31, 2014. Restricted Equity Securities. The Company, as a member of the Federal Reserve Bank and the Federal Home Loan Bank (“FHLB”), is required to maintain investments in each of the organization’s capital stock. As of December 31, 2015 , restricted equity securities of the Federal Reserve Bank and the Federal Home Loan Bank of $ 16,421 and $ 10,135 , respectively, were included in other assets at cost. As of December 31, 2014 , restricted equity securities of the Federal Reserve Bank and the Federal Home Loan Bank were $ 16,187 and $ 10,662 , respectively. No ready market exists for these restricted equity securities, and they have no quoted market values. Restricted equity securities are periodically reviewed for impairment based on ultimate recovery of par value. The determination of whether a decline affects the ultimate recovery of par value is influenced by the significance of the decline compared to the cost basis of the restricted equity securities, the length of time a decline has persisted, the impact of legislative and regulatory changes on the issuing organizations and the liquidity positions of the issuing organizations. Based on management’s assessment, no impairment losses were recorded on restricted equity securities during 2015 , 2014 or 2013 . Derivatives and Hedging Activities. For asset and liability management purposes, the Company has entered into interest rate swap contracts to hedge against changes in forecasted cash flows due to interest rate exposures. Interest rate swaps are contracts in which a series of interest payments are exchanged over a prescribed period. The notional amount upon which the interest payments are based is not exchanged. The swap agreements are derivative instruments and convert a portion of the Company’s forecasted variable rate debt to a fixed rate (i.e., cash flow hedge) over the payment term of the interest rate swap. The effective portion of the gain or loss on cash flow hedging instruments is initially reported as a component of other comprehensive income and subsequently reclassified into earnings in the same period during which the transaction affects earnings. The ineffective portion of the gain or loss on derivative instruments, if any, is recognized in earnings. The Company does not enter into interest rate swap agreements for trading or speculative purposes. The Company also enters into certain interest rate swap contracts that are not designated as hedging instruments. These derivative contracts relate to transactions in which the Company enters into an interest rate swap with a customer while at the same time entering into an offsetting interest rate swap with a third party financial institution. Because the Company acts as an intermediary for the customer, changes in the fair value of the underlying derivative contracts for the most part offset each other and do not significantly impact the Company's results of operations. The Company has residential real estate derivatives for commitments to fund certain residential real estate loans (interest rate locks) to be sold into the secondary market and forward commitments for the future delivery of residential real estate loans to third party investors on a mandatory or best efforts basis. It is the Company’s practice to enter into forward commitments for the future delivery of residential real estate loans when interest rate lock commitments are entered into in order to economically hedge the effect of changes in interest rates resulting from its commitments to fund the loans. Income from Fiduciary Activities . Consistent with industry practice, income for trust services is recognized on the basis of cash received. However, use of this method in lieu of accrual basis accounting does not materially affect reported earnings. Earnings Per Common Share . Basic and diluted earnings per common share are calculated using a two-class method. Under the two-class method, basic earnings per common share is calculated by dividing net income available to common shareholders by the weighted average number of common shares outstanding during the period, excluding outstanding participating securities. Participating securities include non-vested performance restricted stock awards granted prior to 2014 and all non-vested time restricted stock awards. Diluted earnings per common share is calculated by dividing net income available to common shareholders by the weighted average number of common shares outstanding determined for the basic earnings per share calculation plus the dilutive effect of stock compensation using the treasury stock method. Income Taxes . The Parent Company and its subsidiaries have elected to be included in a consolidated federal income tax return. For state income tax purposes, the combined taxable income of the Parent Company and its subsidiaries is apportioned among the states in which operations take place. Federal and state income taxes attributable to the subsidiaries, computed on a separate return basis, are paid to or received from the Parent Company. The Company accounts for income taxes using the liability method. Under the liability method, deferred tax assets and liabilities are determined based on enacted income tax rates which will be in effect when the differences between the financial statement carrying values and tax bases of existing assets and liabilities are expected to be reported in taxable income. Positions taken in the Company’s tax returns may be subject to challenge by the taxing authorities upon examination. Uncertain tax positions are initially recognized in the financial statements when it is more likely than not the position will be sustained upon examination by the tax authorities. Such tax positions are both initially and subsequently measured as the largest amount of tax benefit that is greater than 50% likely of being realized upon settlement with the tax authority, assuming full knowledge of the position and all relevant facts. The Company provides for interest and, in some cases, penalties on tax positions that may be challenged by the taxing authorities. Interest expense is recognized beginning in the first period that such interest would begin accruing. Penalties are recognized in the period that the Company claims the position in the tax return. Interest and penalties on income tax uncertainties are classified within income tax expense in the income statement. With few exceptions, the Company is no longer subject to U.S. federal and state examinations by tax authorities for years before 2012. The Company had accrued interest of $235, $206 and $176 as of December 31, 2015 , 2014 or 2013 . The Company had no penalties as of December 31, 2015 , 2014 or 2013 . Comprehensive Income. Comprehensive income includes net income, as well as other changes in stockholders’ equity that result from transactions and economic events other than those with shareholders. In addition to net income, the Company’s comprehensive income includes the after tax effect of changes in unrealized gains and losses on available-for-sale investment securities and derivatives designated as cash flow hedges, changes in the unamortized gain or loss on available-for-sale investment securities transferred to held-to-maturity and changes in net actuarial gains and losses on defined benefit post-retirement benefits plans. Segment Reporting. An operating segment is defined as a component of a business for which separate financial information is available that is evaluated regularly by the chief operating decision maker in deciding how to allocate resources and evaluate performance. The Company has one operating segment, community banking, which encompasses commercial and consumer banking services offered to individuals, businesses, municipalities and other entities. Advertising Costs. Advertising costs are expensed as incurred. Advertising expense was $3,452 , $3,734 , and $3,532 in 2015 , 2014 and 2013 , respectively. Transfers of Financial Assets. Transfers of financial assets are accounted for as sales when control over the assets has been surrendered. Control over transferred assets is deemed to be surrendered when the assets have been isolated from the Company; the transferee obtains the right, free of conditions that constrain it from taking advantage of that right, to pledge or exchange the transferred assets; and, the Company does not maintain effective control over the transferred assets through an agreement to repurchase them before their maturity. Stock-Based Compensation . Compensation cost for all stock-based awards is measured at fair value on the date of grant and is recognized over the requisite service period for awards expected to vest. Stock-based compensation expense of $ 3,959 , $ 3,634 and $ 2,936 for the years ended December 31, 2015 , 2014 and 2013 , respectively, is included in benefits expense in the Company’s consolidated statements of income. Related income tax benefits recognized for the years ended December 31, 2015 , 2014 and 2013 were $ 1,443 , $ 1,390 and $ 1,122 , respectively. Fair Value Measurements. In general, fair value measurements are based upon quoted market prices, where available. If quoted market prices are not available, fair value measurements are estimated using relevant market information and other assumptions. Fair value estimates involve uncertainties and require some degree of judgment regarding interest rates, credit risk, prepayments and other factors. The use of different assumptions or estimation techniques may have a significant effect on the fair value amounts reported.

Acquisitions

Acquisitions	12 Months Ended
	Dec. 31, 2015
Business Combinations [Abstract]
Mergers, Acquisitions and Dispositions Disclosures	On July 24, 2015 , the Company acquired all of the outstanding stock of Absarokee Bancorporation, Inc. ("Absarokee"), a Montana-based bank holding company operating one subsidiary bank, United Bank, with branches located in three Montana communities adjacent to the Company's existing market areas. As a result of the acquisition, the Company increased its presence in the state of Montana. The Company merged United Bank with and into FIB immediately subsequent to the acquisition. The Company paid cash consideration for the acquisition of $ 7,234 . On July 31, 2014 , the Company acquired all of the outstanding stock of Mountain West Financial Corp ("MWFC"), a Montana-based bank holding company operating one subsidiary bank, Mountain West Bank, NA ("MWB"), with branches located in five of the Company's current market areas in Montana. The Company merged MWB with and into FIB on October 17, 2014 . The acquisition allowed the Company to gain market share in several of its current market areas. The Company also benefited from cost savings related to the merger of MWB with FIB. Consideration for the acquisition of $ 74,451 consisted of cash of $38,479 and the issuance of 1,378,230 shares of the Company's Class A common stock valued at $26.10 per share, the closing price of the Company's Class A common stock as quoted on the NASDAQ stock market on the acquisition date. The Absarokee and MWFC acquisitions were accounted for using the acquisition method with cash consideration funded from cash on hand. The assets and liabilities of the acquired entities were recorded in the Company's consolidated financial statements at their estimated fair values as of the acquisition dates. The excess value of the consideration paid over the fair value of assets acquired and liabilities assumed was recorded as goodwill. Goodwill arising from the acquisitions consists largely of the synergies and economies of scale expected from combining the operations of the acquired entities and the Company. These acquisitions were accounted for as tax-free exchanges; therefore, goodwill recorded in conjunction with the acquisitions is not deductible for income tax purposes. Fair values of assets acquired and liabilities assumed as part of the Absarokee and MWFC acquisitions were estimated using relevant market information and significant other inputs and generally fall within Levels 2 and 3 of the fair value hierarchy. The following table summarizes the consideration paid, fair values of the assets acquired and liabilities assumed and the resulting goodwill. During 2015 , the Company completed its review of MWFC tax items and finalized the fair value of acquired deferred tax assets resulting in a $ 1,199 decrease in goodwill. Absarokee MWFC July 24, 2015 July 31, 2014 Assets acquired: Cash and cash equivalents $ 5,598 $ 74,035 Investment securities 27,574 104,911 Loans 36,644 360,272 Allowance for loan losses — — Premises and equipment 3,128 29,436 Company-owned life insurance — 13,046 Core deposit intangible assets 695 11,014 Other assets 898 18,885 Total assets acquired 74,537 611,599 Liabilities assumed: Deposits 63,565 515,379 Repurchase agreements 2,000 — Long term debt 1,253 — Subordinated debentures held by subsidiary trusts — 20,439 Other liabilities 633 23,231 Total liabilities assumed 67,451 559,049 Net assets acquired 7,086 52,550 Consideration paid: Cash 7,234 38,479 Class A common stock — 35,972 Total consideration paid 7,234 74,451 Goodwill $ 148 $ 21,901 Core deposit intangible assets related to the Absarokee and MWFC acquisitions of $ 695 and $11,014 , respectively, are being amortized using an accelerated method over the estimated useful lives of the related deposits of 10 years. The Company recorded third party acquisition-related costs of $ 795 and $ 4,017 in 2015 and 2014 , respectively. These costs are included in acquisition expenses in the Company's consolidated statements of income. The accompanying consolidated statements of income include the results of operations of the acquired entities from their acquisition dates. The operations of Absarokee and MWFC were immediately integrated with the Company's operations and the acquired banks were merged with FIB. As such, the Company has determined it is not practical to report post-acquisition date revenues and net income of the acquired entities that were included in the Company's consolidated income statements for the years ended December 31, 2015 and 2014. Unaudited pro forma consolidated revenues and net income as if the Absarokee acquisition had occurred as of January 1, 2014, are not presented because the effect of this acquisition was not considered significant. The following table presents unaudited pro forma consolidated revenues and net income as if the MWFC acquisition had occurred as of January 1, 2013. Year ended December 31, (unaudited) 2014 2013 Interest income $ 280,102 $ 280,455 Non-interest income 114,984 120,005 Total revenues $ 395,086 $ 400,460 Net income $ 87,129 $ 84,264 The unaudited pro forma net income presented in the table above for 2014 was adjusted to exclude acquisition-related costs, including change in control expenses related to employee benefit plans, stock option cancellation fees and legal and professional expenses, of $ 5,052 , net of tax. Pro forma net income presented in the table above for 2013 was adjusted to include the aforementioned acquisition-related costs. The unaudited pro forma net income presented in the table above for 2014 and 2013 includes adjustments for scheduled amortization of core deposit intangible assets acquired in the acquisition. No adjustments were made for operating costs savings and other business synergies expected as a result of the acquisition, or accretion or amortization of fair value adjustments other than core deposit intangible assets.

Investment Securities

Investment Securities	12 Months Ended
	Dec. 31, 2015
Investments, Debt and Equity Securities [Abstract]
Investment Securities	INVESTMENT SECURITIES The amortized cost and approximate fair values of investment securities are summarized as follows: December 31, 2015 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Estimated Fair Value Available-for-Sale U.S. Treasury notes $ 3,912 $ 3 $ (4 ) $ 3,911 Obligations of U.S. government agencies 521,079 712 (1,610 ) 520,181 U.S. agency residential mortgage-backed securities & collateralized mortgage obligations 921,699 9,448 (2,101 ) 929,046 Private mortgage-backed securities 156 1 (1 ) 156 Other investments 3,550 5 (9 ) 3,546 Total $ 1,450,396 $ 10,169 $ (3,725 ) $ 1,456,840 December 31, 2015 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Estimated Fair Value Held-to Maturity State, county and municipal securities $ 173,785 $ 5,103 $ (227 ) $ 178,661 Corporate securities 50,046 64 (220 ) 49,890 U.S agency residential mortgage-backed securities & 376,480 7,686 (5,522 ) 378,644 Other investments 354 1 — 355 Total $ 600,665 $ 12,854 $ (5,969 ) $ 607,550 Gross gains of $ 156 and gross losses of $ 19 were realized on the disposition of available-for-sale securities in 2015 . December 31, 2014 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Estimated Fair Value Available-for-Sale Obligations of U.S. government agencies $ 725,408 $ 895 $ (5,370 ) $ 720,933 U.S. agency residential mortgage-backed securities & collateralized mortgage obligations 982,764 11,526 (3,624 ) 990,666 Private mortgage-backed securities 322 5 (2 ) 325 Total $ 1,708,494 $ 12,426 $ (8,996 ) $ 1,711,924 December 31, 2014 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Estimated Fair Value Held-to Maturity State, county and municipal securities $ 188,941 $ 5,949 $ (386 ) $ 194,504 Corporate securities 32,565 54 (75 ) 32,544 U.S. agency residential mortgage-backed securities & collateralized mortgage obligations 353,176 5,563 (1,758 ) 356,981 Other securities 504 — — 504 Total $ 575,186 $ 11,566 $ (2,219 ) $ 584,533 Gross gains of $ 274 and $49 were realized on the disposition of available-for-sale securities in 2014 and 2013 , respectively. Gross losses of $213 and $48 were realized on the disposition of available-for-sale securities in 2014 and 2013 , respectively. As of December 31, 2015 , the Company had general obligation securities with amortized costs of $ 140,458 included in state, county and municipal securities, of which $ 78,337 were issued by political subdivisions or agencies within the states of Montana, Wyoming and South Dakota. On October 30, 2015 , the Company transferred available-for-sale U.S. agency residential mortgage-backed securities and collateralized mortgage obligations with amortized costs and fair values of $ 100,343 and $ 100,140 , respectively, into the held-to-maturity category. Unrealized net losses of $ 203 included in accumulated other comprehensive income at the time of the transfer are being amortized to yield over the remaining expected lives of the transferred securities of 4.0 years . On June 27, 2014 , the Company transferred available-for-sale U.S. agency residential mortgage-backed securities and collateralized mortgage obligations with amortized costs and fair values of $ 396,640 and $ 388,808 , respectively, into the held-to-maturity category. Unrealized net losses of $ 7,832 at the time of the transfer are being amortized to yield over the remaining expected lives of the transferred securities of 4.3 years . The following tables show the gross unrealized losses and fair values of investment securities, aggregated by investment category, and the length of time individual investment securities have been in a continuous unrealized loss position, as of December 31, 2015 and 2014 . Less than 12 Months 12 Months or More Total December 31, 2015 Fair Value Gross Unrealized Losses Fair Value Gross Unrealized Losses Fair Value Gross Unrealized Losses Available-for-Sale U.S. Treasury notes $ 2,092 $ (4 ) $ — $ — $ 2,092 $ (4 ) Obligations of U.S. government agencies 209,631 (1,077 ) 54,619 (533 ) 264,250 (1,610 ) U.S. agency residential mortgage-backed securities & collateralized mortgage obligations 343,875 (1,577 ) 28,010 (524 ) 371,885 (2,101 ) Private mortgage-backed securities — — 61 (1 ) 61 (1 ) Other investments 1,225 (9 ) — — 1,225 (9 ) Total $ 556,823 $ (2,667 ) $ 82,690 $ (1,058 ) $ 639,513 $ (3,725 ) Less than 12 Months 12 Months or More Total December 31, 2015 Fair Value Gross Unrealized Losses Fair Value Gross Unrealized Losses Fair Value Gross Unrealized Losses Held-to-Maturity State, county and municipal securities $ 10,182 $ (39 ) $ 9,476 $ (188 ) $ 19,658 $ (227 ) U.S. agency residential mortgage-backed 87,033 (4,390 ) 69,539 (1,132 ) 156,572 (5,522 ) Corporate securities 31,135 (220 ) — — 31,135 (220 ) Total $ 128,350 $ (4,649 ) $ 79,015 $ (1,320 ) $ 207,365 $ (5,969 ) Less than 12 Months 12 Months or More Total December 31, 2014 Fair Value Gross Unrealized Losses Fair Value Gross Unrealized Losses Fair Value Gross Unrealized Losses Available-for-Sale Obligations of U.S. government agencies $ 135,888 $ (702 ) $ 309,283 $ (4,668 ) $ 445,171 $ (5,370 ) U.S. agency residential mortgage-backed securities & collateralized mortgage obligations 219,214 (887 ) 151,380 (2,737 ) 370,594 (3,624 ) Private mortgage-backed securities — — 90 (2 ) 90 (2 ) Total $ 355,102 $ (1,589 ) $ 460,753 $ (7,407 ) $ 815,855 $ (8,996 ) Less than 12 Months 12 Months or More Total December 31, 2014 Fair Value Gross Unrealized Losses Fair Value Gross Unrealized Losses Fair Value Gross Unrealized Losses Held-to-Maturity State, county and municipal securities $ 7,979 $ (13 ) $ 20,097 $ (373 ) $ 28,076 $ (386 ) U.S. agency residential mortgage-backed securities & collateralized mortgage obligations 61,201 (1,758 ) — — $ 61,201 $ (1,758 ) Corporate securities 14,755 (75 ) — — 14,755 (75 ) Total $ 83,935 $ (1,846 ) $ 20,097 $ (373 ) $ 104,032 $ (2,219 ) The investment portfolio is evaluated quarterly for other-than-temporary declines in the market value of each individual investment security. Consideration is given to the length of time and the extent to which the fair value has been less than cost; the financial condition and near term prospects of the issuer; and, the intent and ability of the Company to retain its investment in the issuer for a period of time sufficient to allow for any anticipated recovery in fair value. As of December 31, 2015 , the Company had 198 individual investment securities that were in an unrealized loss position. As of December 31, 2014 , the Company had 154 individual investment securities that were in an unrealized loss position. Unrealized losses as of December 31, 2015 and 2014 related primarily to fluctuations in the current interest rates. The fair value of these investment securities is expected to recover as the securities approach their maturity or repricing date or if market yields for such investments decline. As of December 31, 2015 , the Company had the intent and ability to hold these investment securities for a period of time sufficient to allow for an anticipated recovery. Furthermore, the Company does not have the intent to sell any of the available-for-sale securities in the above table and it is more likely than not that the Company will not have to sell any securities before a recovery in cost. No impairment losses were recorded during 2015 , 2014 or 2013 . Maturities of investment securities at December 31, 2015 are shown below. Maturities of mortgage-backed securities have been adjusted to reflect shorter maturities based upon estimated prepayments of principal. All other investment securities maturities are shown at contractual maturity dates. Available-for-Sale Held-to-Maturity December 31, 2015 Amortized Cost Estimated Fair Value Amortized Cost Estimated Fair Value Within one year $ 329,638 $ 331,620 $ 100,695 $ 101,885 After one year but within five years 1,018,573 1,022,351 320,310 322,281 After five years but within ten years 46,874 47,117 134,606 137,304 After ten years 55,311 55,752 45,054 46,080 Total $ 1,450,396 $ 1,456,840 $ 600,665 $ 607,550 At December 31, 2015 , the Company had investment securities callable within one year with amortized costs and estimated fair values of $ 98,885 and $ 98,664 , respectively. These investment securities are primarily classified as available-for-sale and included in the after one year but within five years category in the table above. At December 31, 2015 , the Company had no callable structured notes. Maturities of securities do not reflect rate repricing opportunities present in adjustable rate mortgage-backed securities. At December 31, 2015 and 2014 , the Company had variable rate mortgage-backed securities with amortized costs of $68,440 and $40,666 , respectively, classified as available-for-sale in the table above. There are no significant concentrations of investments at December 31, 2015 , (greater than 10 percent of stockholders’ equity) in any individual security issuer, except for U.S. government or agency-backed securities. Investment securities with amortized cost of $1,325,078 and $1,351,787 at December 31, 2015 and 2014 , respectively, were pledged to secure public deposits and securities sold under repurchase agreements. The approximate fair value of securities pledged at December 31, 2015 and 2014 was $1,328,571 and $1,356,341 , respectively. All securities sold under repurchase agreements are with customers and mature on the next banking day. The Company retains possession of the underlying securities sold under repurchase agreements.

Loans

Loans	12 Months Ended
	Dec. 31, 2015
Receivables [Abstract]
Loans	LOANS The following table presents loans by class as of the dates indicated: December 31, 2015 2014 Real estate loans: Commercial $ 1,793,258 $ 1,639,422 Construction: Land acquisition & development 224,066 220,443 Residential 111,763 96,580 Commercial 94,890 101,246 Total construction loans 430,719 418,269 Residential 1,032,851 999,903 Agricultural 156,234 167,659 Total real estate loans 3,413,062 3,225,253 Consumer: Indirect consumer 622,529 552,863 Other consumer 153,717 144,141 Credit card 68,107 65,467 Total consumer loans 844,353 762,471 Commercial 792,416 740,073 Agricultural 142,151 124,859 Other, including overdrafts 1,339 3,959 Loans held for investment 5,193,321 4,856,615 Mortgage loans held for sale 52,875 40,828 Total loans $ 5,246,196 $ 4,897,443 The Company has lending policies and procedures in place that are designed to maximize loan income within an acceptable level of risk. Management reviews and approves these policies and procedures on a regular basis. A reporting system supplements the review process by providing management with frequent reports related to loan production, loan quality, concentrations of credit, loan delinquencies and internally risk-classified loans. Real estate loans include construction and permanent financing for both single-family and multi-unit properties, term loans for commercial, agricultural and industrial property and/or buildings and home equity loans and lines of credit secured by real estate. Longer-term residential real estate loans are generally sold in the secondary market. Those residential real estate loans not sold are typically secured by first liens on the financed property and generally mature in less than fifteen years . Home equity loans and lines of credit are typically secured by first or second liens on residential real estate and generally do not exceed a loan to value ratio of 80% . The Company had home equity loans and lines of credit of $ 298,661 and $ 298,692 as of December 31, 2015 and 2014 , respectively. Commercial and agricultural real estate loans are generally secured by first liens on income-producing real estate and generally mature in less than 5 years . Construction loans are primarily to commercial builders for residential lot development and the construction of single-family residences and commercial real estate properties. Construction loans are generally underwritten pursuant to pre-approved permanent financing. During the construction phase the borrower pays interest only. Consumer loans include direct personal loans, credit card loans, lines of credit and indirect dealer loans for the purchase of automobiles, recreational vehicles, boats and other consumer goods. Personal loans and indirect dealer loans are generally secured by automobiles, boats and other types of personal property and are made on an installment basis. Credit cards are offered to individuals in our market areas. Lines of credit are generally floating rate loans that are unsecured or secured by personal property. Commercial loans include a mix of variable and fixed rate loans made to small and medium-sized manufacturing, wholesale, retail and service businesses for working capital needs and business expansions. Commercial loans generally include lines of credit, business credit cards and loans with maturities of five years or less. The loans are generally made with business operations as the primary source of repayment, but also include collateralization by inventory, accounts receivable, equipment and/or personal guarantees. Agricultural loans generally consist of short and medium-term loans and lines of credit that are primarily used for crops, livestock, equipment and general operations. Agricultural loans are ordinarily secured by assets such as livestock or equipment and are repaid from the operations of the farm or ranch. Agricultural loans generally have maturities of five years or less, with operating lines for one production season. Included in the loan table above, are loans acquired in business combinations including certain loans that had evidence of deterioration in credit quality since origination and for which it was probable, at acquisition, that all contractually required payments would not be collected. The following table displays the outstanding unpaid principal balance, accrued interest receivable and accrual status of loans acquired with credit impairment as of December 31, 2015 and 2014 . December 31, 2015 2014 Outstanding balance $ 33,755 $ 41,910 Carrying value: Loans on accrual status 21,507 31,870 Loans on non-accrual status — — Total carrying value $ 21,507 $ 31,870 The following table summarizes changes in the accretable yield for loans acquired credit impaired for year ended December 31, 2015 and 2014 : Year Ended December 31, 2015 2014 Beginning balance $ 5,781 $ — Acquisitions 432 5,233 Accretion income (2,884 ) (735 ) Additions 594 — Reductions due to exit events (517 ) (201 ) Reclassifications from nonaccretable differences 3,307 1,484 Ending balance $ 6,713 $ 5,781 Loans are considered past due if the required principal and interest payments have not been received as of the date such payments were due. The following tables present the contractual aging of the Company’s recorded investment in past due loans by class as of the period indicated: Total Loans 30 - 59 60 - 89 > 90 30 or More Days Days Days Days Current Non-accrual Total As of December 31, 2015 Past Due Past Due Past Due Past Due Loans Loans Loans Real estate Commercial $ 6,051 $ 724 $ 418 $ 7,193 $ 1,762,294 $ 23,771 $ 1,793,258 Construction: Land acquisition & development 3,190 163 1,325 4,678 212,757 6,631 224,066 Residential 1,288 — — 1,288 110,182 293 111,763 Commercial 3,232 — — 3,232 90,703 955 94,890 Total construction loans 7,710 163 1,325 9,198 413,642 7,879 430,719 Residential 5,991 1,196 2,063 9,250 1,018,359 5,242 1,032,851 Agricultural 176 17 — 193 150,686 5,355 156,234 Total real estate loans 19,928 2,100 3,806 25,834 3,344,981 42,247 3,413,062 Consumer: Indirect consumer 6,675 1,089 210 7,974 614,029 526 622,529 Other consumer 1,312 331 34 1,677 151,381 659 153,717 Credit card 533 317 477 1,327 66,768 12 68,107 Total consumer loans 8,520 1,737 721 10,978 832,178 1,197 844,353 Commercial 8,493 1,060 699 10,252 759,851 22,313 792,416 Agricultural 879 152 62 1,093 140,430 628 142,151 Other, including overdrafts — — 314 314 1,025 — 1,339 Loans held for investment 37,820 5,049 5,602 48,471 5,078,465 66,385 5,193,321 Mortgage loans originated for sale — — — — 52,875 — 52,875 Total loans $ 37,820 $ 5,049 $ 5,602 $ 48,471 $ 5,131,340 $ 66,385 $ 5,246,196 Total Loans 30 - 59 60 - 89 > 90 30 or More Days Days Days Days Current Non-accrual Total As of December 31, 2014 Past Due Past Due Past Due Past Due Loans Loans Loans Real estate Commercial $ 4,692 $ 1,609 $ 331 $ 6,632 $ 1,605,421 $ 27,369 $ 1,639,422 Construction: Land acquisition & development 839 383 — 1,222 210,969 8,252 220,443 Residential — 475 — 475 95,833 272 96,580 Commercial 100 — — 100 98,582 2,564 101,246 Total construction loans 939 858 — 1,797 405,384 11,088 418,269 Residential 6,969 645 1,762 9,376 987,735 2,792 999,903 Agricultural 1,624 236 — 1,860 158,957 6,842 167,659 Total real estate loans 14,224 3,348 2,093 19,665 3,157,497 48,091 3,225,253 Consumer: Indirect consumer 3,235 482 6 3,723 548,757 383 552,863 Other consumer 988 140 32 1,160 142,432 549 144,141 Credit card 369 284 315 968 64,484 15 65,467 Total consumer loans 4,592 906 353 5,851 755,673 947 762,471 Commercial 3,659 994 147 4,800 722,575 12,698 740,073 Agricultural 1,125 — — 1,125 123,288 446 124,859 Other, including overdrafts — — — — 3,959 — 3,959 Loans held for investment 23,600 5,248 2,593 31,441 4,762,992 62,182 4,856,615 Mortgage loans originated for sale — — — — 40,828 — 40,828 Total loans $ 23,600 $ 5,248 $ 2,593 $ 31,441 $ 4,803,820 $ 62,182 $ 4,897,443 Acquired loans that meet the criteria for non-accrual of interest prior to the acquisition were considered performing upon acquisition. If interest on non-accrual loans had been accrued, such income would have approximated $3,150 , $3,970 and $4,630 during the years ended December 31, 2015 , 2014 and 2013 , respectively. The Company considers impaired loans to include all loans, except consumer loans, that are risk rated as doubtful, or have been placed on non-accrual status or renegotiated in troubled debt restructurings. The following tables present information on the Company’s recorded investment in impaired loans as of dates indicated: December 31, 2015 Unpaid Total Principal Balance Recorded Investment With No Allowance Recorded Investment With Allowance Total Recorded Investment Related Allowance Real estate: Commercial $ 58,179 $ 27,882 $ 17,614 $ 45,496 $ 3,401 Construction: Land acquisition & development 15,503 7,245 778 8,023 282 Residential 992 293 — 293 — Commercial 1,264 340 739 1,079 739 Total construction loans 17,759 7,878 1,517 9,395 1,021 Residential 7,073 3,547 2,317 5,864 367 Agricultural 6,434 5,563 198 5,761 5 Total real estate loans 89,445 44,870 21,646 66,516 4,794 Commercial 29,593 10,744 13,727 24,471 6,487 Agricultural 1,349 622 356 978 294 Total $ 120,387 $ 56,236 $ 35,729 $ 91,965 $ 11,575 December 31, 2014 Unpaid Total Principal Balance Recorded Investment With No Allowance Recorded Investment With Allowance Total Recorded Investment Related Allowance Real estate: Commercial $ 41,603 $ 28,143 $ 11,246 $ 39,389 $ 1,608 Construction: Land acquisition & development 12,511 7,262 1,615 8,877 574 Residential 459 272 — 272 — Commercial 2,729 253 2,442 2,695 904 Total construction loans 15,699 7,787 4,057 11,844 1,478 Residential 2,959 2,452 341 2,793 143 Agricultural 8,844 6,444 2,305 8,749 732 Total real estate loans 69,105 44,826 17,949 62,775 3,961 Commercial 16,904 11,882 2,644 14,526 1,190 Agricultural 1,231 342 837 1,179 641 Total $ 87,240 $ 57,050 $ 21,430 $ 78,480 $ 5,792 December 31, 2013 Unpaid Total Principal Balance Recorded Investment With No Allowance Recorded Investment With Allowance Total Recorded Investment Related Allowance Real estate: Commercial $ 64,780 $ 29,216 $ 33,937 $ 63,153 $ 5,210 Construction: Land acquisition & development 23,906 9,901 7,226 17,127 1,434 Residential 1,816 1,095 277 1,372 26 Commercial 397 279 84 363 85 Total construction loans 26,119 11,275 7,587 18,862 1,545 Residential 9,448 5,081 967 6,048 249 Agricultural 8,895 6,429 2,370 8,799 335 Total real estate loans 109,242 52,001 44,861 96,862 7,339 Commercial 15,448 10,684 2,901 13,585 1,504 Agricultural 177 39 86 125 86 Total $ 124,867 $ 62,724 $ 47,848 $ 110,572 $ 8,929 The following tables present the average recorded investment in and income recognized on impaired loans for the periods indicated: Year Ended December 31, 2015 2014 2013 Average Recorded Investment Income Recognized Average Recorded Investment Income Recognized Average Recorded Investment Income Recognized Real estate: Commercial $ 39,233 $ 784 $ 54,701 $ 876 $ 66,330 $ 1,092 Construction: Land acquisition & development 8,337 54 13,056 43 19,523 487 Residential 282 — 822 — 1,893 — Commercial 1,887 7 1,529 8 3,936 4 Total construction loans 10,506 61 15,407 51 25,352 491 Residential 4,055 1 4,537 5 8,104 17 Agricultural 7,156 39 8,774 78 8,230 8 Total real estate loans 60,950 885 83,419 1,010 108,016 1,608 Commercial 18,502 123 13,789 50 15,047 68 Agricultural 858 26 447 23 313 16 Total $ 80,310 $ 1,034 $ 97,655 $ 1,083 $ 123,376 $ 1,692 The amount of interest income recognized by the Company within the period that the loans were impaired was primarily related to loans modified in troubled debt restructurings that remained on accrual status. Interest payments received on non-accrual impaired loans are applied to principal. Interest income is subsequently recognized only to the extent cash payments are received in excess of principal due. If interest on impaired loans had been accrued, interest income on impaired loans during 2015 , 2014 and 2013 would have been approximately $ 3,935 , $ 4,951 and $ 5,786 , respectively. Collateral dependent impaired loans are recorded at the fair value less selling costs of the underlying collateral determined using discounted cash flows, independent appraisals and management estimates based upon current market conditions. For loans measured under the present value of cash flows method, the change in present value attributable to the passage of time, if applicable, is recognized in the provision for loan losses and thus no interest income is recognized. Modifications of performing loans are made in the ordinary course of business and are completed on a case-by-case basis as negotiated with the borrower. Loan modifications typically include interest rate changes, interest only periods of less than twelve months, short-term payment deferrals and extension of amortization periods to provide payment relief. A loan modification is considered a troubled debt restructuring if the borrower is experiencing financial difficulties and the Company, for economic or legal reasons, grants a concession to the borrower that it would not otherwise consider. Certain troubled debt restructurings are on non-accrual status at the time of restructuring and may be returned to accrual status after considering the borrower's sustained repayment performance in accordance with the restructuring agreement for a period of at least six months and management is reasonably assured of future performance. If the troubled debt restructuring meets these performance criteria and the interest rate granted at the modification is equal to or greater than the rate that the Company was willing to accept at the time of the restructuring for a new loan with comparable risk, then the loan will return to performing status and the accrual of interest will resume, although they continue to be individually evaluated for impairment and disclosed as impaired loans. The Company had loans renegotiated in troubled debt restructurings of $ 40,330 as of December 31, 2015 , of which $ 24,911 were included in non-accrual loans and $ 15,419 were on accrual status. The Company had loans renegotiated in troubled debt restructurings of $ 44,227 as of December 31, 2014 , of which $ 23,275 were included in non-accrual loans and $ 20,952 were on accrual status. The following table presents information on the Company's troubled debt restructurings that occurred during the periods indicated: Number of Notes Type of Concession Principal Balance at Restructure Date Year Ended December 31, 2015 Interest only period Extension of terms or maturity Interest rate adjustment Other Commercial Real Estate 2 $ — $ 628 $ — $ 54 $ 682 Indirect Consumer 1 — — — 4 4 Commercial 12 — 8,689 3,318 455 12,462 Total 15 $ — $ 9,317 $ 3,318 $ 513 $ 13,148 Number of Notes Type of Concession Principal Balance at Restructure Date Year ended December 31, 2014 Interest only period Extension of terms or maturity Interest rate adjustment Other Real estate: Commercial 13 $ 4,753 $ 672 $ 84 $ 1,047 $ 6,556 Residential 1 — — — 15 15 Total real estate loans 14 4,753 672 84 1,062 6,571 Consumer 1 — 113 — — 113 Commercial 5 476 — — 30 506 Total 20 $ 5,229 $ 785 $ 84 $ 1,092 $ 7,190 Number of Notes Type of Concession Principal Balance at Restructure Date Year ended December 31, 2013 Interest only period Extension of terms or maturity Interest rate adjustment Other Real estate: Commercial 19 $ 543 $ 1,378 $ 11,420 $ 2,310 $ 15,651 Construction: Land acquisition & development 8 528 7,308 1,952 — 9,788 Residential 3 — 408 411 — 819 Total construction loans 11 528 7,716 2,363 — 10,607 Residential 5 — 708 — 79 787 Agriculture 1 — — 188 — 188 Total real estate loans 36 1,071 9,802 13,971 2,389 27,233 Consumer 1 — — 27 — 27 Commercial 6 613 178 265 87 1,143 Total 43 $ 1,684 $ 9,980 $ 14,263 $ 2,476 $ 28,403 Other concessions include payment reductions or deferrals for a specified period of time or the extension of amortization schedules. A specific reserve may have been previously recorded for loans modified in troubled debt restructurings that were on non-accrual status or otherwise deemed impaired before the modification. In periods subsequent to modification, the Company continues to evaluate all loans modified in troubled debt restructurings for possible impairment, which is recognized through the allowance for loan losses. Financial effects of modifications may include principal loan forgiveness or other charge-offs directly related to the restructuring. The Company had no charge-offs directly related to loans modified in troubled debt restructurings taken at the time of restructuring during 2015 , 2014 or 2013 . The Company considers a payment default to occur on loans modified in troubled debt restructurings when the loan is 90 days or more past due or was placed on non-accrual status after the modification. The following table presents information on the Company's troubled debt restructurings during the previous 12 months for which there was a payment default. Year ended December 31, 2015 Number of Notes Balance Indirect Consumer 1 $ 4 Commercial 2 240 Total 3 $ 244 As of December 31, 2014 and 2013 , loans modified in troubled debt restructurings within the previous 12 months for which there was a payment default during the period were not significant. As of December 31, 2015 , and 2014 , all of the loans modified in troubled debt restructurings with payment defaults during the previous twelve months were on non-accrual status. At December 31, 2015 , there were no material commitments to lend additional funds to borrowers whose existing loans have been renegotiated or are classified as non-accrual. As part of the on-going and continuous monitoring of the credit quality of the Company’s loan portfolio, management tracks internally assigned risk classifications of loans. The Company adheres to a Uniform Classification System developed jointly by the various bank regulatory agencies to internally risk rate loans. The Uniform Classification System defines three broad categories of criticized assets, which the Company uses as credit quality indicators: Other Assets Especially Mentioned — includes loans that exhibit weaknesses in financial condition, loan structure or documentation, which if not promptly corrected, may lead to the development of abnormal risk elements. Substandard — includes loans that are inadequately protected by the current sound worth and paying capacity of the borrower. Although the primary source of repayment for a Substandard is not currently sufficient; collateral or other sources of repayment are sufficient to satisfy the debt. Continuance of a Substandard loan is not warranted unless positive steps are taken to improve the worthiness of the credit. Doubtful — includes loans that exhibit pronounced weaknesses to a point where collection or liquidation in full, on the basis of currently existing facts, conditions and values, is highly questionable and improbable. Doubtful loans are required to be placed on non-accrual status and are assigned specific loss exposure. The following tables present the Company’s recorded investment in criticized loans by class and credit quality indicator based on the most recent analysis performed as of the dates indicated: As of December 31, 2015 Other Assets Especially Mentioned Substandard Doubtful Total Criticized Loans Real estate: Commercial $ 61,787 $ 84,556 $ 10,609 $ 156,952 Construction: Land acquisition & development 16,593 12,482 591 29,666 Residential 1,640 1,886 — 3,526 Commercial 166 323 756 1,245 Total construction loans 18,399 14,691 1,347 34,437 Residential 4,453 9,661 2,540 16,654 Agricultural 6,114 16,529 — 22,643 Total real estate loans 90,753 125,437 14,496 230,686 Consumer: Indirect consumer 644 1,131 154 1,929 Other consumer 651 1,130 198 1,979 Total consumer loans 1,295 2,261 352 3,908 Commercial 32,975 27,982 15,085 76,042 Agricultural 2,247 7,105 417 9,769 Total $ 127,270 $ 162,785 $ 30,350 $ 320,405 As of December 31, 2014 Other Assets Especially Mentioned Substandard Doubtful Total Criticized Loans Real estate: Commercial $ 84,533 $ 83,448 $ 15,246 $ 183,227 Construction: Land acquisition & development 11,826 15,016 2,507 29,349 Residential 2,029 2,666 — 4,695 Commercial 39 253 2,442 2,734 Total construction loans 13,894 17,935 4,949 36,778 Residential 10,473 10,848 1,121 22,442 Agricultural 10,122 12,328 612 23,062 Total real estate loans 119,022 124,559 21,928 265,509 Consumer: Indirect consumer 916 1,590 121 2,627 Other consumer 553 1,085 432 2,070 Credit card — 348 1,263 1,611 Total consumer loans 1,469 3,023 1,816 6,308 Commercial 25,766 32,433 10,273 68,472 Agricultural 7,827 3,660 837 12,324 Total $ 154,084 $ 163,675 $ 34,854 $ 352,613 The Company maintains a credit review function, which is independent of the credit approval process, to assess assigned internal risk classifications and monitor compliance with internal lending policies and procedures. Written action plans with firm target dates for resolution of identified problems are maintained and reviewed on a quarterly basis for all categories of criticized loans.

Allowance For Loan Losses

Allowance For Loan Losses	12 Months Ended
	Dec. 31, 2015
Receivables [Abstract]
Allowance For Loan Losses	ALLOWANCE FOR LOAN LOSSES The following table presents a summary of changes in the allowance for loan losses by portfolio segment: Year ended December 31, 2015 Real Estate Consumer Commercial Agriculture Other Total Allowance for loan losses: Beginning balance $ 53,884 $ 5,035 $ 14,307 $ 974 $ — $ 74,200 Provision charged (credited) to operating expense (645 ) 3,243 4,376 (152 ) — 6,822 Less loans charged-off (4,076 ) (5,683 ) (1,657 ) (221 ) — (11,637 ) Add back recoveries of loans previously charged-off 3,133 2,549 1,749 1 — 7,432 Ending balance $ 52,296 $ 5,144 $ 18,775 $ 602 $ — $ 76,817 Individually evaluated for impairment $ 4,794 $ — $ 6,487 $ 294 $ — $ 11,575 Collectively evaluated for impairment 47,502 5,144 12,288 308 — 65,242 Ending balance $ 52,296 $ 5,144 $ 18,775 $ 602 $ — $ 76,817 Total loans: Individually evaluated for impairment $ 66,516 $ — $ 24,471 $ 978 $ — $ 91,965 Collectively evaluated for impairment 3,346,546 844,353 767,945 141,173 1,339 5,101,356 Total loans held for investment $ 3,413,062 $ 844,353 $ 792,416 $ 142,151 $ 1,339 $ 5,193,321 Year ended December 31, 2014 Real Estate Consumer Commercial Agriculture Other Total Allowance for loan losses: Beginning balance $ 63,923 $ 6,193 $ 14,747 $ 476 $ — $ 85,339 Provision charged (credited) to operating expense (10,348 ) 1,382 1,809 535 — (6,622 ) Less loans charged-off (3,014 ) (4,887 ) (6,030 ) (64 ) — (13,995 ) Add back recoveries of loans previously charged-off 3,323 2,347 3,781 27 — 9,478 Ending balance $ 53,884 $ 5,035 $ 14,307 $ 974 $ — $ 74,200 Individually evaluated for impairment $ 3,961 $ — $ 1,190 $ 641 $ — $ 5,792 Collectively evaluated for impairment 49,923 5,035 13,117 333 — 68,408 Ending balance $ 53,884 $ 5,035 $ 14,307 $ 974 $ — $ 74,200 Total loans: Individually evaluated for impairment $ 62,775 $ — $ 14,526 $ 1,179 $ — $ 78,480 Collectively evaluated for impairment 3,162,478 762,471 725,547 123,680 3,959 4,778,135 Total loans held for investment $ 3,225,253 $ 762,471 $ 740,073 $ 124,859 $ 3,959 $ 4,856,615 Year ended December 31, 2013 Real Estate Consumer Commercial Agriculture Other Total Allowance for loan losses: Beginning balance $ 75,782 $ 7,141 $ 17,085 $ 503 $ — $ 100,511 Provision charged (credited) to operating expense (7,722 ) 1,605 41 (49 ) — (6,125 ) Less loans charged-off (10,224 ) (4,612 ) (5,672 ) (5 ) — (20,513 ) Add back recoveries of loans previously charged-off 6,087 2,059 3,293 27 — 11,466 Ending balance $ 63,923 $ 6,193 $ 14,747 $ 476 $ — $ 85,339 Individually evaluated for impairment $ 7,339 $ — $ 1,504 $ 86 $ — $ 8,929 Collectively evaluated for impairment 56,584 6,193 13,243 390 — 76,410 Ending balance $ 63,923 $ 6,193 $ 14,747 $ 476 $ — $ 85,339 Total loans: Individually evaluated for impairment $ 96,862 $ — $ 13,585 $ 125 $ — $ 110,572 Collectively evaluated for impairment 2,745,393 671,587 662,959 111,747 1,734 4,193,420 Total loans held for investment $ 2,842,255 $ 671,587 $ 676,544 $ 111,872 $ 1,734 $ 4,303,992 The Company performs a quarterly assessment of the adequacy of its allowance for loan losses in accordance with generally accepted accounting principles. The methodology used to assess the adequacy is consistently applied to the Company's loan portfolio and consists of three elements: (1) specific valuation allowances based on probable losses on impaired loans; (2) historical valuation allowances based on loan loss experience for similar loans with similar characteristics and trends; and (3) general valuation allowances determined based on changes in the nature of the loan portfolio, overall portfolio quality, industry concentrations, delinquency trends, general economic conditions and other qualitative risk factors both internal and external to the Company. Specific allowances are established for loans where management has determined that probability of a loss exists by analyzing the borrower’s ability to repay amounts owed, collateral deficiencies and any relevant qualitative or environmental factors impacting the loan. Historical valuation allowances are determined by applying percentage loss factors to the credit exposures from outstanding loans. For commercial, agricultural and real estate loans, loss factors are applied based on the internal risk classifications of these loans. For consumer loans, loss factors are applied on a portfolio basis. For commercial, agriculture and real estate loans, loss factor percentages are based on a migration analysis of our historical loss experience, designed to account for credit deterioration. For consumer loans, loss factor percentages are based on a one-year loss history. General valuation allowances are determined by evaluating, on a quarterly basis, changes in the nature and volume of the loan portfolio, overall portfolio quality, industry concentrations, current economic and regulatory factors and the estimated impact of current economic, environmental and regulatory conditions on historical loss rates. An allowance for loan losses is established for loans acquired credit impaired and for which the Company projects a decrease in the expected cash flows in periods subsequent to the acquisition of such loans. As of December 31, 2015 and 2014 , the Company's allowance for loans losses included $382 and $ 287 , respectively, related to acquired credit impaired loans.

Premises and Equipment

Premises and Equipment	12 Months Ended
	Dec. 31, 2015
Property, Plant and Equipment [Abstract]
Premises and Equipment	PREMISES AND EQUIPMENT Premises and equipment and related accumulated depreciation are as follows: December 31, 2015 2014 Land $ 37,999 $ 40,620 Buildings and improvements 213,321 209,328 Furniture and equipment 81,354 74,959 332,674 324,907 Less accumulated depreciation (141,862 ) (129,695 ) Premises and equipment, net $ 190,812 $ 195,212 The Parent Company and a FIB branch office lease premises from an affiliated entity. See Note 17—Commitments and Contingencies.

Company - Owned Life Insurance

Company - Owned Life Insurance	12 Months Ended
	Dec. 31, 2015
Investments, All Other Investments [Abstract]
Company-Owned Life Insurance	COMPANY-OWNED LIFE INSURANCE Company-owned life insurance consists of the following: December 31, 2015 2014 Key executive, principal shareholder $ 3,926 $ 3,798 Key executive split dollar 4,778 4,707 Group life 178,549 145,316 Total $ 187,253 $ 153,821 The Company maintains key executive life insurance policies on certain principal shareholders. Under these policies, the Company receives benefits payable upon the death of the insured. The net cash surrender value of key executive, principal shareholder insurance policies was $3,926 and $3,798 at December 31, 2015 and 2014 , respectively. The Company also has life insurance policies covering selected other key officers. The net cash surrender value of these policies was $4,778 and $4,707 at December 31, 2015 and 2014 , respectively. Under these policies, the Company receives benefits payable upon death of the insured. An endorsement split dollar agreement has been executed with the selected key officers whereby a portion of the policy death benefit is payable to their designated beneficiaries. The endorsement split dollar agreement will provide post-retirement coverage for those selected key officers meeting specified retirement qualifications. The Company expenses the earned portion of the post-employment benefit through the vesting period. The Company has group life insurance policies covering selected officers of FIB. The net cash surrender value of these policies was $178,549 and $145,316 at December 31, 2015 and 2014 , respectively. Under these policies, the Company receives benefits payable upon death of the insured. The Company has entered into either an endorsement split dollar agreement or a survivor income benefit agreement with each insured officer. Under the endorsement split dollar agreements, a portion of the policy death benefit is payable to the insured's designated beneficiary if the insured is employed by the Company at the time of death. Under the survivor income benefit agreements, the Company makes a lump-sum payment to the insured's designated beneficiary if the insured is employed by the Company at the time of death.

Other Real Estate Owned

Other Real Estate Owned	12 Months Ended
	Dec. 31, 2015
Repossessed Assets [Abstract]
Other Real Estate Owned	OTHER REAL ESTATE OWNED Information with respect to the Company’s other real estate owned follows: Year Ended December 31, 2015 2014 2013 Balance at beginning of year $ 13,554 $ 15,504 $ 32,571 Acquisitions — 3,608 — Additions 5,560 5,198 11,545 Capitalized improvements — — 65 Valuation adjustments (207 ) (224 ) (3,512 ) Dispositions (12,653 ) (10,532 ) (25,165 ) Balance at end of year $ 6,254 $ 13,554 $ 15,504 Write-downs of $207 during 2015 included adjustments of $ 106 directly related to receipt of updated appraisals and adjustments of $ 101 based on other sources, including management estimates of the current fair value of properties. Write-downs of $224 during 2014 included adjustments of $ 93 directly related to receipt of updated appraisals and adjustments of $ 131 based on other sources, including management estimates of the current fair value of properties. Write-downs of $3,512 during 2013 included adjustments of $1,083 directly related to receipt of updated appraisals and adjustments of $2,429 based on other sources, including management estimates of the current fair value of properties.

Derivatives and Hedging

Derivatives and Hedging	12 Months Ended
	Dec. 31, 2015
Derivative [Line Items]
Derivative Instruments and Hedging Activities Disclosure [Text Block]	DERIVATIVES AND HEDGING ACTIVITIES The notional amounts and estimated fair values of the Company's interest rate swap contracts are presented in the following table. December 31, 2015 December 31, 2014 Notional Amount Estimated Fair Value Notional Amount Estimated Fair Value Derivatives designated as hedges: Interest rate swap $ 100,000 $ 165 $ — $ — Non-hedging interest rate derivatives: Interest rate swap-assets 9,369 788 3,200 61 Interest rate swap-liabilities 9,369 829 3,200 59 On September 22, 2015 , the Company entered into a forward starting interest rate swap with a notional amount of $100,000 that was designated as a cash flow hedge. Under the terms of the interest rate swap contract, the Company pays a fixed interest rate of 1.94% and the counterparty pays to the Company a variable interest rate equal to the three-month LIBOR. No cash is exchanged until the effective date, which begins on September 15, 2017 and ends on September 15, 2020. The Company designated the interest payments related to future Federal Home Loan Bank or other borrowings as the cash flow hedge. The hedge was fully effective during the current period. As such, no amount of ineffectiveness was included in the Company's income statement in 2015. The fair value of the interest rate swap is included in other liabilities in the Company's balance sheet with changes in fair value recorded in other comprehensive income. The Company expects the hedge to remain highly effective during the remaining term of the interest rate swap. The following table presents the pre-tax gains or losses related to the interest rate swap derivative contracts recorded in accumulated other comprehensive income and other non-interest income in the Company's statements of income: As of or For The Year Ended December 31, 2015 2014 Derivatives designated as hedges: Amount of gain recognized in other comprehensive income (effective portion) $ 165 $ — Non-hedging interest rate derivatives: Amount of gain (loss) recognized in other non-interest income (43 ) 2

Mortgage Servicing Rights

Mortgage Servicing Rights	12 Months Ended
	Dec. 31, 2015
Transfers and Servicing [Abstract]
Mortgage Servicing Rights	MORTGAGE SERVICING RIGHTS Information with respect to the Company’s mortgage servicing rights follows: Year Ended December 31, 2015 2014 2013 Balance at beginning of year $ 14,374 $ 14,018 $ 13,224 Acquisitions of mortgage servicing rights 306 — — Originations of mortgage servicing rights 3,614 2,717 3,581 Amortization expense (2,434 ) (2,361 ) (2,787 ) Balance at end of year 15,860 14,374 14,018 Less valuation reserve (239 ) (336 ) (472 ) Balance at end of year $ 15,621 $ 14,038 $ 13,546 Principal balance of serviced loans underlying mortgage servicing rights $ 2,906,239 $ 2,615,311 $ 2,416,621 Mortgage servicing rights as a percentage of serviced loans 0.54 % 0.54 % 0.56 % At December 31, 2015 , the estimated fair value and weighted average remaining life of the Company’s mortgage servicing rights were $ 31,011 and 7.3 years, respectively. The fair value of mortgage servicing rights was determined using discount rates ranging from 9.8% to 14.5% and monthly prepayment speeds ranging from 0.5% to 1.8% depending upon the risk characteristics of the underlying loans. The Company reversed impairment of $97 , $136 and $99 in 2015 , 2014 and 2013 , respectively. No permanent impairment was recorded in 2015 , 2014 or 2013 .

Deposits

Deposits	12 Months Ended
	Dec. 31, 2015
Deposits [Abstract]
Deposits	DEPOSITS Deposits are summarized as follows: December 31, 2015 2014 Non-interest bearing demand $ 1,823,716 $ 1,791,364 Interest bearing: Demand 2,178,373 2,133,273 Savings 1,955,256 1,843,355 Time, $100 and over 487,372 520,125 Time, other 644,220 718,095 Total interest bearing 5,265,221 5,214,848 Total deposits $ 7,088,937 $ 7,006,212 The Company had no brokered time deposits as of December 31, 2015 and 2014 . Other time deposits include deposits obtained through the Company’s participation in the Certificate of Deposit Account Registry Service (“CDARS”). CDARS deposits totaled $38,336 and $40,491 as of December 31, 2015 and 2014 , respectively. As of December 31, 2015 and 2014 , the Company had time deposits of $222,912 and $228,410 , respectively, that met or exceeded the FDIC insurance limit of $250 . Maturities of time deposits at December 31, 2015 are as follows: Time, $100 and Over Total Time Due within 3 months or less $ 109,343 $ 309,819 Due after 3 months and within 6 months 82,059 161,333 Due after 6 months and within 12 months 131,381 266,174 Due after 12 months 164,589 394,266 Total $ 487,372 $ 1,131,592 Interest expense on time deposits of $100 or more was $3,739 , $4,003 and $4,880 for the years ended December 31, 2015 , 2014 and 2013 , respectively.

Long-Term Debt and Other Borrow

Long-Term Debt and Other Borrowed Funds	12 Months Ended
	Dec. 31, 2015
Debt Disclosure [Abstract]
Long-Term Debt and Other Borrowed Funds	LONG-TERM DEBT AND OTHER BORROWED FUNDS A summary of long-term debt follows: December 31, 2015 2014 Parent Company: 6.81% subordinated term loan maturing January 9, 2018, principal due at maturity, interest payable quarterly $ 20,000 $ 20,000 Subsidiaries: Variable rate subordinated term loan maturing February 28, 2018, principal due at maturity, interest payable quarterly — 15,000 4.86% note payable to FHLB, maturing October 31, 2015 — 225 8.00% capital lease obligation with term ending October 25, 2029 1,582 1,643 6.24% note payable maturing September 2032, principal due at maturity, interest payable monthly 1,343 1,199 2.28% note payable maturing July 29, 2022, principal due at maturity, interest payable monthly 4,960 — Total long-term debt $ 27,885 $ 38,067 Maturities of long-term debt at December 31, 2015 are as follows: 2016 $ 65 2017 71 2018 20,077 2019 83 2020 90 Thereafter 7,499 Total $ 27,885 On January 10, 2008, the Company borrowed $20,000 on a 6.81% unsecured subordinated term loan maturing January 9, 2018 , with interest payable quarterly and principal due at maturity. A portion of the unsecured subordinated term loan qualifies as tier 2 capital under regulatory capital adequacy guidelines. During February 2008, the Company borrowed $15,000 on a variable rate unsecured subordinated term loan maturing February 28, 2018 , with interest payable quarterly and principal due at maturity. The Company elected at various dates an interest rate equal to either prime or LIBOR plus 2.00% . The Company repaid this note on November 30, 2015. No prepayment penalties were incurred in conjunction with the early repayment. Unamortized debt issuance costs of $7 were charged to expense in 2015. The Company has available lines of credit with the FHLB of approximately $ 752,639 , subject to collateral availability. As of December 31, 2015 , there were no long or short-term advances outstanding with the FHLB. As of December 31, 2014 , FHLB advances of $ 225 , which were secured by a blanket assignment of the Company’s qualifying residential and commercial real estate loans, were included in long-term debt. The Company has a capital lease obligation on a banking office. The balance of the obligation was $ 1,582 and $ 1,643 as of December 31, 2015 and 2014 , respectively. Assets acquired under capital lease, consisting solely of a building and leasehold improvements, are included in premises and equipment and are subject to depreciation. In conjunction with the MWFC acquisition, the Company assumed a 6.24% fixed rate unsecured note payable maturing in September, 2032 , with interest payable monthly and principal due at maturity. The balance of the obligation was $1,343 and $1,199 as of December 31, 2015 and 2014 , respectively. On January 29, 2015 , the Company borrowed $ 4,960 on a 2.28% note payable maturing July 29, 2022 , with interest payable monthly and principal due at maturity. The note is collateralized by the Company's equity interest in Universal Sub CDE, LLC, a CDE owned 99.9% by the Company. The Company had other borrowed funds of $ 2 and $ 9 as of December 31, 2015 and 2014 , respectively, consisting of demand notes issued to the United States Treasury, secured by investment securities and bearing no interest. The Company has federal funds lines of credit with third parties amounting to $ 165,000 , subject to funds availability. These lines are subject to cancellation without notice. The Company also has a line of credit with the Federal Reserve Bank for borrowings up to $ 407,739 secured by a blanket pledge of indirect consumer loans.

Subordinated Debentures Held by

Subordinated Debentures Held by Subsidiary Trusts	12 Months Ended
	Dec. 31, 2015
Subordinated Borrowings [Abstract]
Subordinated Debentures Held by Subsidiary Trusts	SUBORDINATED DEBENTURES HELD BY SUBSIDIARY TRUSTS The Company sponsors six wholly-owned business trusts, Trust I, Trust II, Trust III, Trust IV, Trust V and Trust VI (collectively, the “Trusts”). The Trusts were formed for the exclusive purpose of issuing an aggregate of $80,000 of 30-year floating rate mandatorily redeemable capital trust preferred securities (“Trust Preferred Securities”) to third-party investors. The Trusts also issued, in aggregate, $2,477 of common equity securities to the Parent Company. Proceeds from the issuance of the Trust Preferred Securities and common equity securities were invested in 30-year junior subordinated deferrable interest debentures (“Subordinated Debentures”) issued by the Parent Company. A summary of Subordinated Debenture issuances follows: Principal Amount Outstanding as of December 31, Issuance Maturity Date 2015 2014 October 2007 January 1, 2038 $ 10,310 $ 10,310 November 2007 December 15, 2037 15,464 15,464 December 2007 December 15, 2037 20,619 20,619 December 2007 April 1, 2038 15,464 15,464 January 2008 April 1, 2038 10,310 10,310 January 2008 April 1, 2038 10,310 10,310 Total subordinated debentures held by subsidiary trusts $ 82,477 $ 82,477 In October 2007 , the Company issued $ 10,310 of Subordinated Debentures to Trust II. The Subordinated Debentures bear a cumulative floating interest rate equal to LIBOR plus 2.25% per annum. As of December 31, 2015 the interest rate on the Subordinated Debentures was 2.58% . In November 2007 , the Company issued $ 15,464 of Subordinated Debentures to Trust I. The Subordinated Debentures bore interest at a fixed rate of 7.50% for five years after issuance until December 16, 2012, and thereafter at a variable rate equal to LIBOR plus 2.75% per annum. As of December 31, 2015 , the interest rate on the Subordinated Debentures was 3.26% . In December 2007 , the Company issued $ 20,619 of Subordinated Debentures to Trust III. The Subordinated Debentures bore interest at a fixed rate of 6.88% for five years after issuance until December 15, 2012, and thereafter at a variable rate equal to LIBOR plus 2.40% per annum. As of December 31, 2015 , the interest rate on the Subordinated Debentures was 2.91% . In December 2007 , the Company issued $ 15,464 of Subordinated Debentures to Trust IV. The Subordinated Debentures bear a cumulative floating interest rate equal to LIBOR plus 2.70% per annum. As of December 31, 2015 the interest rate on the Subordinated Debentures was 3.03% . In January 2008 , the Company issued $ 10,310 of Subordinated Debentures to Trust V. The Subordinated Debentures bore interest at a fixed rate of 6.78% for five years after issuance until April 1, 2013, and thereafter at a variable rate equal to LIBOR plus 2.75% per annum. As of December 31, 2015 the interest rate on the Subordinated Debentures was 3.08% . In January 2008 , the Company issued $ 10,310 of Subordinated Debentures to Trust VI. The Subordinated Debentures bear a cumulative floating interest rate equal to LIBOR plus 2.75% per annum. As of December 31, 2015 , the interest rate on the Subordinated Debentures was 3.08% . The Subordinated Debentures are unsecured with interest distributions payable quarterly. The Company may defer the payment of interest at any time provided that the deferral period does not extend past the stated maturity. During any such deferral period, distributions on the Trust Preferred Securities will also be deferred and the Company’s ability to pay dividends on its common and preferred shares is restricted. The Subordinated Debentures may be redeemed, subject to approval by the Federal Reserve Bank, at the Company’s option on or after five years from the date of issue, or at any time in the event of unfavorable changes in laws or regulations. Debt issuance costs consisting primarily of underwriting discounts and professional fees were capitalized and are being amortized through maturity to interest expense using the straight-line method, which approximates level yield. The terms of the Trust Preferred Securities are identical to those of the Subordinated Debentures. The Trust Preferred Securities are subject to mandatory redemption upon repayment of the Subordinated Debentures at their stated maturity dates or earlier redemption in an amount equal to their liquidation amount plus accumulated and unpaid distributions to the date of redemption. The Company guarantees the payment of distributions and payments for redemption or liquidation of the Trust Preferred Securities to the extent of funds held by the Trusts. Subject to certain limitations, the Trust Preferred Securities qualify as tier 1 capital of the Parent Company under the Federal Reserve Board’s capital adequacy guidelines. Proceeds from the issuance of the Trust Preferred Securities were used to fund acquisitions. In conjunction with the acquisition of MWFC on July 31, 2014 , the Company acquired two business trusts, Mountain West Statutory Trust III and Mountain West Statutory Trust IV (collectively, the “Mountain West Trusts”). The Mountain West Trusts were formed for the exclusive purpose of issuing an aggregate of $19,825 of 30-year floating rate mandatorily redeemable capital trust preferred securities (“Mountain West Trust Preferred Securities”) to third-party investors. The Trusts also issued, in aggregate, $614 of common equity securities to MWFC. Proceeds from the issuance of the Trust Preferred Securities and common equity securities were invested in 30-year junior subordinated deferrable interest debentures (“Mountain West Subordinated Debentures”) issued by the MWFC. On December 15, 2014 , the Company redeemed $14,433 of Mountain West Subordinated Debentures bearing a cumulative floating interest rate equal to LIBOR plus 1.85% per annum. The redemption price of $14,433 was equal to the $ 1 liquidation amount of each debenture plus all accrued and unpaid distributions to the date of redemption. The redemption of the Mountain West Subordinated Debentures caused a mandatory redemption of $14,000 of Mountain West trust Preferred Securities and $433 of common equity securities. On December 26, 2014 , the Company redeemed $6,006 of Mountain West Subordinated Debentures bearing a cumulative floating interest rate equal to LIBOR plus 3.10% per annum. The redemption price of $ 6,006 was equal to the $ 1 liquidation amount of each debenture plus all accrued and unpaid distributions to the date of redemption. The redemption of the Mountain West Subordinated Debentures caused a mandatory redemption of $ 5,825 of Mountain West Trust Preferred Securities and $ 181 of common equity securities.

Capital Stock and Dividend Rest

Capital Stock and Dividend Restrictions	12 Months Ended
	Dec. 31, 2015
Equity [Abstract]
Capital Stock and Dividend Restrictions	CAPITAL STOCK AND DIVIDEND RESTRICTIONS The Company's authorized common stock consists of 200,000,000 shares, of which, 100,000,000 shares are designated as Class A common stock and 100,000,000 are designated as Class B common stock. The Class A common stock has one vote per share. The Class B common stock has five votes per share and is convertible to Class A common stock on a share-for-share basis at any time. The Company had 21,698,594 shares of Class A common stock and 23,729,631 shares of Class B common stock outstanding as of December 31, 2015 . The Company had 21,928,932 shares of Class A common stock and 23,859,483 shares of Class B common stock outstanding as of December 31, 2014 . During 2015 , the Company issued 21,414 shares of its Class A common stock with an aggregate value of $591 to directors for their service on the Company's board of directors during 2015 . During 2014 , the Company issued 24,581 shares of its Class A common stock with an aggregate value of $620 to directors for their service on the Company's board of directors during 2014 . In addition, on July 31, 2014 , the Company issued 1,378,230 shares of its Class A common stock with an aggregate value of $35,972 as partial consideration for the acquisition of MWFC. During 2015 , the Company repurchased and retired 765,875 shares of its Class A common stock in a combination of open market and privately negotiated transactions at an aggregate purchase price of $19,921 , or a weighted average price of $26.01 per share. The repurchases were made pursuant to a stock repurchase program approved by the Company's board of directors. All other stock repurchases during 2015 and 2014 were redemptions of vested restricted shares tendered in lieu of cash for payment of income tax withholding amounts by participants of the Company's 2006 Equity Compensation Plan. On April 3, 2015, the Company filed a Registration Statement on Form S-8 to register 2,000,000 shares of Class A common stock to be issued pursuant to the Company's 2015 Equity and Incentive Plan. On January 24, 2014 , the Company filed a Registration Statement on Form S-8 to register 1,500,000 shares of Class A common stock to be issued pursuant to the Company's 2006 Equity Compensation Plan, as amended and restated. All shares of common stock available for future grant under the 2006 Equity Compensation Plan, as amended and restated, were transferred into the 2015 Equity and Incentive Plan in April 2015. The payment of dividends by subsidiary banks is subject to various federal and state regulatory limitations. In general, a bank is limited, without the prior consent of its regulators, to paying dividends that do not exceed current year net profits together with retained earnings from the two preceding calendar years. The Company’s debt instruments also include limitations on the payment of dividends.

Earnings per Common Share

Earnings per Common Share	12 Months Ended
	Dec. 31, 2015
Earnings Per Share [Abstract]
Earnings per Common Share	EARNINGS PER COMMON SHARE Basic earnings per common share is calculated by dividing net income by the weighted average number of common shares outstanding during the period presented, excluding unvested restricted stock. Diluted earnings per share is calculated by dividing net income by the weighted average number of common shares determined for the basic earnings per share computation plus the dilutive effects of stock-based compensation using the treasury stock method. The following table sets forth the computation of basic and diluted earnings per common share: Year Ended December 31, 2015 2014 2013 Net income, basic and diluted $ 86,795 $ 84,401 $ 86,136 Weighted average common shares outstanding for basic earnings per share computation 45,184,091 44,615,060 43,566,681 Dilutive effects of stock-based compensation 462,327 595,501 477,921 Weighted average common shares outstanding for diluted earnings per common share computation 45,646,418 45,210,561 44,044,602 Basic earnings per common share $ 1.92 $ 1.89 $ 1.98 Diluted earnings per common share 1.90 1.87 1.96 The Company had 12,890 , 5,000 and 21,372 unvested time restricted stock and stock options outstanding as of December 31, 2015 , 2014 and 2013 , respectively, that were not included in the computation of diluted earnings per common share because their effect would be anti-dilutive. The Company had 142,512 , 88,797 and 37,734 shares of unvested restricted stock as of December 31, 2015 , 2014 and 2013 , respectively, that were not included in the computation of diluted earnings per common share because performance conditions for vesting had not been met.

Regulatory Capital

Regulatory Capital	12 Months Ended
	Dec. 31, 2015
Banking and Thrift [Abstract]
Regulatory Capital	REGULATORY CAPITAL The Company is subject to the regulatory capital requirements administered by federal banking regulators and the Federal Reserve. Failure to meet minimum capital requirements can initiate certain mandatory and possible additional discretionary actions by regulators that, if undertaken, could have a direct material effect on the Company’s financial statements. Under capital adequacy guidelines and the regulatory framework for prompt corrective action, the Company must meet specific capital guidelines that involve quantitative measures of the Company’s assets, liabilities and certain off-balance sheet items as calculated under regulatory accounting practices. The Parent Company, like all bank holding companies, is not subject to the prompt corrective action provisions. Capital amounts and classification are also subject to qualitative judgments by the regulators about components, risk weightings and other factors. Quantitative measures established by regulation to ensure capital adequacy require the Company to maintain minimum amounts and ratios of total and tier 1 capital to risk-weighted assets, and of tier 1 capital to average assets, as defined in the regulations. As of December 31, 2015 , the Company exceeded all capital adequacy requirements to which it is subject. The Company’s actual capital amounts and ratios and selected minimum regulatory thresholds and prompt corrective action provisions as of December 31, 2015 and 2014 are presented in the following tables: Actual Adequately Capitalized Basel III Phase-In Schedule Adequately Capitalized Basel III Fully Phased-In Well Capitalized (1) Amount Ratio Amount Ratio Amount Ratio Amount Ratio December 31, 2015 Total risk-based capital: Consolidated $ 946,156 15.4 % $ 492,692 8.0 % $ 646,658 10.50 % $ 615,865 10.0 % FIB 882,504 14.4 490,866 8.0 644,262 10.50 $ 613,582 10.0 Tier 1 risk-based capital: Consolidated 861,339 14.0 369,519 6.0 523,485 8.5 $ 492,692 8.0 FIB 805,805 13.1 368,149 6.0 521,545 8.5 $ 490,866 8.0 Common equity tier 1 risk-based capital: Consolidated 781,339 12.7 383,040 4.5 595,840 7.0 $ 400,312 6.5 FIB 805,805 13.1 381,730 4.5 593,802 7.0 $ 398,829 6.5 Leverage capital ratio: Consolidated 861,339 10.1 246,346 4.0 246,346 4.0 $ 425,600 5.0 FIB 805,805 9.5 245,433 4.0 245,433 4.0 $ 424,145 5.0 (1) The ratios for the well-capitalized requirement are only applicable to FIB. However, the Company manages its capital position as if the requirement applies to the consolidated entity and has presented the ratios as if they also applied on a consolidated basis. Actual Adequately Capitalized Well Capitalized (1) Amount Ratio Amount Ratio Amount Ratio December 31, 2014 Total risk-based capital: Consolidated $ 897,769 16.2 % $ 444,685 8.0 % $ 555,856 10.0 % FIB 832,907 15.1 442,468 8.0 553,085 10.0 Tier 1 risk-based capital: Consolidated 807,229 14.5 222,343 4.0 $ 333,514 6.0 FIB 754,708 13.7 221,234 4.0 331,851 6.0 Leverage capital ratio: Consolidated 807,229 9.6 335,897 4.0 $ 419,871 5.0 FIB 754,708 9.1 330,006 4.0 412,507 5.0 (1) The ratios for the well-capitalized requirement are only applicable to FIB. However, the Company manages its capital position as if the requirement applies to the consolidated entity and has presented the ratios as if they also applied on a consolidated basis. On July 2, 2013, the Board of Governors of the Federal Reserve Bank issued a final rule implementing a revised regulatory capital framework for U.S. banks in accordance with the Basel III international accord and satisfying related mandates under the Dodd-Frank Wall Street Reform and Consumer Protection Act. The revised regulatory capital framework (the "Basel III Capital Rules") substantially revised the risk-based capital requirements applicable to bank holding companies and depository institutions by defining the components of capital and addressing other issues affecting the numerator in banking institutions’ regulatory capital ratios, addressing risk weights and other issues affecting the denominator in banking institutions’ regulatory capital ratios and replacing the existing risk-weighting approach with a more risk-sensitive approach. The Basel III Capital Rules became effective for the Company on January 1, 2015, subject to a phase-in period for certain provisions.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2015
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	COMMITMENTS AND CONTINGENCIES FIB was a defendant in a lender liability lawsuit, Kelly Logging Inc. v. First Interstate Bank (the “case"), which was tried in August 2014 in the Montana Fourth Judicial District Court in Missoula, Montana. The case was settled on August 31, 2015. Legal and settlement costs related to the case of $ 5,000 and $ 4,000 during 2015 and 2014, respectively, are included in loss contingency expenses in the Company's consolidated statements of income. In the normal course of business, the Company is involved in various other claims and litigation. In the opinion of management, following consultation with legal counsel, the ultimate liability or disposition thereof is not expected to have a material adverse effect on the consolidated financial condition, results of operations or liquidity of the Company. The Company had commitments under construction contracts of $ 1,341 as of December 31, 2015 . As of December 31, 2015, the Company also had a commitment under a forward starting interest rate swap with a notional amount of $ 100,000 . For additional information about the forward starting interest rate swap, see Note 9 — Derivatives and Hedging Activity. The Parent Company and the Billings office of FIB are the anchor tenants in a building owned by an entity in which FIB has a 50% ownership interest. The Company leases certain premises and equipment from third parties under operating leases. Total rental expense to third parties was $ 2,660 in 2015 , $ 1,190 in 2014 and $ 1,403 in 2013 . The total future minimum rental commitments, exclusive of maintenance and operating costs, required under operating leases that have initial or remaining noncancelable lease terms in excess of one year at December 31, 2015 , are as follows: Third Parties Related Entity Total For the year ending December 31: 2016 $ 1,913 $ 290 $ 2,203 2017 1,800 249 2,049 2018 1,537 138 1,675 2019 1,487 — 1,487 2020 1,349 — 1,349 Thereafter 8,655 — 8,655 Total $ 16,741 $ 677 $ 17,418 Residential mortgage loans sold to investors in the secondary market are sold with varying recourse provisions. Essentially all of the loan sales agreements require the repurchase of a mortgage loan by the seller in situations such as breach of representation, warranty or covenant; untimely document delivery; false or misleading statements; failure to obtain certain certificates or insurance; unmarketability; etc. Certain loan sales agreements contain repurchase requirements based on payment-related defects that are defined in terms of the number of days or months since the purchase, the sequence number of the payment, and/or the number of days of payment delinquency. Based on the specific terms stated in the agreements, the Company had $ 3,465 and $ 4,486 of sold residential mortgage loans with recourse provisions still in effect as of December 31, 2015 and 2014 , respectively. The Company did not repurchase any significant amount of loans from secondary market investors under the terms of loan sales agreements during the years ended December 31, 2015 , 2014 and 2013 . In the opinion of management, the risk of recourse and the subsequent requirement of loan repurchase to the Company is not significant, and accordingly no liabilities have been established related to such. In addition, the Company made various representations and warranties associated with the sale of loans. The Company has not incurred significant losses resulting from these provisions.

Financial Instruments with Off-

Financial Instruments with Off-Balance Sheet Risk	12 Months Ended
	Dec. 31, 2015
Financial Instruments with Off-Balance Sheet Risk [Abstract]
Financial Instruments with Off-Balance Sheet Risk	FINANCIAL INSTRUMENTS WITH OFF-BALANCE SHEET RISK The Company is a party to financial instruments with off-balance sheet risk in the normal course of business to meet the financing needs of its customers. These financial instruments include commitments to extend credit and standby letters of credit. These instruments involve, to varying degrees, elements of credit and interest rate risk in excess of amounts recorded in the consolidated balance sheet. The Company evaluates each customer’s creditworthiness on a case-by-case basis. The amount of collateral obtained is based on management’s credit evaluation of the customer. Collateral held varies but may include accounts receivable, inventory, premises and equipment, and income-producing commercial properties. Commitments to extend credit are agreements to lend to a customer as long as there is no violation of any condition established in the commitment contract. Commitments generally have fixed expiration dates or other termination clauses and may require payment of a fee. Generally, commitments to extend credit are subject to annual renewal. Since many of the commitments are expected to expire without being drawn upon, the total commitment amounts do not necessarily represent future cash requirements. Commitments to extend credit to borrowers approximated $ 1,401,686 at December 31, 2015 , which included $ 581,695 on unused credit card lines and $ 388,752 with commitment maturities beyond one year. Commitments to extend credit to borrowers approximated $ 1,415,119 at December 31, 2014 , which included $ 476,752 on unused credit card lines and $ 363,609 with commitment maturities beyond one year. Standby letters of credit are conditional commitments issued by the Company to guarantee the performance of a customer to a third party. Most commitments extend for no more than two years and are generally subject to annual renewal. The credit risk involved in issuing letters of credit is essentially the same as that involved in extending loan facilities to customers. At December 31, 2015 and 2014 , the Company had outstanding stand-by letters of credit of $ 52,250 and $ 58,950 , respectively. The estimated fair value of the obligation undertaken by the Company in issuing standby letters of credit is included in accounts payable and accrued expenses in the Company’s consolidated balance sheets.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Income Taxes	INCOME TAXES Income tax expense consists of the following: Year ended December 31, 2015 2014 2013 Current: Federal $ 26,741 $ 34,941 $ 30,757 State 4,472 4,928 4,533 Total current 31,213 39,869 35,290 Deferred: Federal 11,047 4,870 10,056 State 1,402 475 1,220 Total deferred 12,449 5,345 11,276 Total income tax expense $ 43,662 $ 45,214 $ 46,566 Total income tax expense differs from the amount computed by applying the statutory federal income tax rate of 35 percent in 2015 , 2014 and 2013 to income before income taxes as a result of the following: Year ended December 31, 2015 2014 2013 Tax expense at the statutory tax rate $ 45,660 $ 45,365 $ 46,446 Increase (decrease) in tax resulting from: Tax-exempt income (4,092 ) (4,255 ) (3,620 ) State income tax, net of federal income tax benefit 3,791 3,541 3,741 Federal tax credits (2,249 ) (313 ) (353 ) Other, net 552 876 352 Tax expense at effective tax rate $ 43,662 $ 45,214 $ 46,566 The tax effects of temporary differences between the financial statement carrying amounts and tax bases of assets and liabilities that give rise to significant portions of the net deferred tax asset (liability) relate to the following: December 31, 2015 2014 Deferred tax assets: Loans, principally due to allowance for loan losses $ 28,999 $ 28,506 Lease costs 596 719 Loss contingencies 108 1,785 Loan discount 4,552 7,022 Investment securities, unrealized losses 2,093 2,728 Employee benefits 9,009 8,256 Other real estate owned write-downs and carrying costs 598 2,536 Deferred gain on sale of subsidiary — 253 Deferred revenue on contract 1,087 481 Other 126 760 Deferred tax assets 47,168 53,046 Deferred tax liabilities: Fixed assets, principally differences in bases and depreciation (5,140 ) (569 ) Investment securities, unrealized gains (2,538 ) (1,351 ) Investment in joint venture partnership, principally due to differences in depreciation of partnership assets (1,301 ) (1,053 ) Prepaid amounts (1,139 ) (1,385 ) Government agency stock dividends (2,442 ) (2,407 ) Goodwill and core deposit intangibles (39,886 ) (36,732 ) Mortgage servicing rights (4,422 ) (4,144 ) Other (65 ) (531 ) Deferred tax liabilities (56,933 ) (48,172 ) Net deferred tax assets (liabilities) $ (9,765 ) $ 4,874 The Company had a current net income tax payable of $ 6,275 at December 31, 2015 and $4,693 at December 31, 2014 , which are included in accounts payable and accrued expenses.

Stock-Based Compensation

Stock-Based Compensation	12 Months Ended
	Dec. 31, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Stock-Based Compensation	STOCK-BASED COMPENSATION The Company has equity awards outstanding under three stock-based compensation plans; the 2015 Equity Incentive Plan (the "2015 Plan"), the 2006 Equity Compensation Plan, as amended and restated, (the “2006 Plan”) and the 2001 Stock Option Plan. These plans were primarily established to enhance the Company’s ability to attract, retain and motivate employees. The Company’s Board of Directors or, upon delegation, the Compensation Committee of the Board of Directors (“Compensation Committee”) has exclusive authority to select employees, advisors and others, including directors, to receive awards and to establish the terms and conditions of each award made pursuant to the Company’s stock-based compensation plans. The 2015 Plan, approved by the Company’s shareholders in May 2015, was established to provide the Company with flexibility to select from various equity-based performance compensation methods, and to be able to address changing accounting and tax rules and corporate governance practices by optimally utilizing performance based compensation. The 2015 Plan did not increase the number of shares of common stock available for awards under the 2006 Plan. The 2006 Plan, approved by the Company’s shareholders in May 2006 and May 2014, was established to consolidate into one plan the benefits available under the 2001 Stock Option Plan and all other then existing share-based award plans (collectively with the 2006 Plan, the “Previous Plans”). The Previous Plans continue with respect to awards made prior to June 2015. All shares of common stock available for future grant under the Previous Plans were transferred into the 2015 Plan. At December 31, 2015 , there were 1,987,379 common shares available for future grant under the 2015 Plan. All stock based compensation awards granted subsequent to March 29, 2010 are for shares of Class A common stock. All awards granted prior to March 29, 2010 are for shares of Class B common stock. Stock Options. All options granted have an exercise price equal to fair market value, which is currently defined as the closing sales price for the stock as quoted on the NASDAQ Stock Market for the last market trading day preceding the date that the Company’s Board of Directors awards the benefit. Options may be subject to vesting as determined by the Company's Board of Directors or Compensation Committee, and can be exercised for periods of up to ten years from the date of grant. Compensation expense related to stock option awards of $ 481 , $ 905 and $ 1,390 was included in benefits on the Company’s consolidated income statements for the years ended December 31, 2015 , 2014 and 2013 , respectively. Related income tax benefits recognized for the years ended December 31, 2015 , 2014 and 2013 were $ 184 , $ 346 and $ 531 , respectively. No stock option awards were granted in 2015 or 2014 . The weighted average grant date fair value of options granted was $ 3.54 during 2013 . The fair value of each option award is estimated on the date of grant using the Black-Scholes option pricing model. Weighted-average assumptions used in the option pricing model for 2013 awards included an expected volatility rate of 30.61% , an expected dividend yield of 3.00% , a risk-free interest rate of 0.88% and an expected life of the options granted of 5.52 years. Expected dividend yield is based on the Company’s annualized expected dividends per share divided by the average common stock price. Risk-free interest rate is based on the U.S. treasury constant maturity yield for treasury securities with maturities approximating the expected life of the options granted on the date of grant. The expected life of options is based on the Company’s historical exercise and post-vesting termination behaviors. Expected volatility is based on the historical volatility of the Company's common stock since the Company's initial public offering, which concluded on March 29, 2010 . The following table summarizes stock option activity under the Company’s active stock option plans for the year ended December 31, 2015 : Number of Shares Weighted-Average Exercise Price Weighted-Average Remaining Contract Life Outstanding options, beginning of year 1,748,032 $ 17.01 Exercised (350,438 ) 16.77 Forfeited (10,216 ) 16.82 Outstanding options, end of year 1,387,378 $ 17.06 3.68 years Outstanding options exercisable, end of year 1,265,596 $ 17.05 3.64 years The total intrinsic value of fully-vested stock options outstanding as of December 31, 2015 was $ 15,218 . The total intrinsic value of options exercised was $ 3,931 , $ 7,363 and $ 7,108 during the years ended December 31, 2015 , 2014 and 2013 , respectively. The actual tax benefit realized for the tax deduction from option exercises totaled $ 1,504 , $ 2,594 and $ 1,963 for the years ended December 31, 2015 , 2014 and 2013 , respectively. The Company received cash of $ 3,369 , $ 6,299 and $ 9,271 from stock option exercises during the years ended December 31, 2015 , 2014 and 2013 , respectively. The Company redeemed common stock with aggregate values of $ 2,507 , $ 6,829 and $ 8,721 tendered in payment for stock option exercises during the years ended December 31, 2015 , 2014 and 2013 , respectively. Information with respect to the Company’s nonvested stock options as of and for the year ended December 31, 2015 follows: Number of Shares Weighted-Average Grant Date Fair Value Nonvested stock options, beginning of year 355,022 $ 3.62 Vested (225,961 ) 3.73 Forfeited (7,279 ) 3.48 Nonvested stock options, end of year 121,782 $ 3.48 As of December 31, 2015 , there was $ 52 of unrecognized compensation cost related to nonvested stock options granted under the Company’s active stock option plans. That cost is expected to be recognized over a weighted-average period of 0 0.12 years. The total fair value of shares vested during 2015 was $ 843 . Restricted Stock Awards. Common stock issued under the Company’s restricted stock plan may not be sold or otherwise transferred until restrictions have lapsed or performance objectives have been obtained. During the vesting periods, participants have voting rights and receive dividends on all time restricted shares and vesting performance restricted shares. Upon termination of employment, common shares upon which restrictions have not lapsed must be returned to the Company. All restricted share awards are classified as equity awards. The fair value of equity-classified restricted stock awards is amortized as compensation expense on a straight-line basis over the period restrictions lapse or performance goals are met. Compensation expense related to restricted stock awards of $ 2,887 , $ 2,109 and $ 1,546 was included in benefits on the Company’s consolidated statements of income for the years ended December 31, 2015 , 2014 and 2013 , respectively. Related income tax benefits recognized for the years ended December 31, 2015 , 2014 and 2013 were $ 1,104 , $ 807 and $ 591 , respectively. The following table presents information regarding the Company’s restricted stock as of December 31, 2015 : Number of Shares Weighted-Average Measurement Date Fair Value Restricted stock, beginning of year 248,399 $ 21.16 Granted 169,577 26.27 Vested (95,153 ) 18.65 Forfeited (16,583 ) 24.07 Canceled (2,601 ) 17.22 Restricted stock, end of year 303,639 $ 25.15 During 2015 , the Company issued 169,577 restricted common shares. The 2015 restricted share awards included 78,378 performance restricted shares of which 26,126 vest in varying percentages upon achievement of defined return on asset performance goals, 26,126 vest in varying percentages upon achievement of defined return on equity performance goals and 26,126 vest in varying percentages upon achievement of defined total return to shareholder goals. Vesting of the performance restricted shares is also contingent on employment as of December 31, 2017 . Additionally, 91,199 time-restricted shares were issued during 2015 that vest one-third on each annual anniversary of the grant date through September 24, 2018 , contingent on continued employment through the vesting date. As of December 31, 2015 , there was $ 4,444 of unrecognized compensation cost related to nonvested restricted stock awards expected to be recognized over a period of 1.80 years.

Employee Benefit Plans

Employee Benefit Plans	12 Months Ended
	Dec. 31, 2015
Compensation Related Costs [Abstract]
Employee Benefit Plans	EMPLOYEE BENEFIT PLANS Profit Sharing Plan. The Company has a noncontributory profit sharing plan. All employees, other than temporary employees, working 20 hours or more per week are eligible to participate in the profit sharing plan. The Company’s Board of Directors authorize contributions to the profit sharing plan that are not to exceed, on an individual basis, the lesser of 100% of compensation or $ 50 annually. Participants become 100% vested upon the completion of three years of vesting service. Accrued contribution expense for this plan of $ 727 , $ 1,509 and $ 1,555 in 2015 , 2014 and 2013 , respectively, is included in employee benefits expense in the Company’s consolidated statements of income. Savings Plan. In addition, the Company has a contributory employee savings plan. Eligibility requirements for this plan are the same as those for the profit sharing plan discussed in the preceding paragraph. Employee participation in the plan is at the option of the employee. The Company contributes $1.25 for each $1.00 of employee contributions up to 4% of the participating employee’s compensation. Accrued contribution expense for this plan of $ 4,683 , $ 4,256 and $ 4,067 in 2015 , 2014 and 2013 , respectively, is included in employee benefits expense in the Company’s consolidated statements of income. Postretirement Healthcare Plan. The Company sponsors a contributory defined benefit healthcare plan (the “Plan”) for active employees and employees and directors retiring from the Company at the age of at least 55 years and with at least 15 years of continuous service. Retired Plan participants contribute the full cost of benefits based on the average per capita cost of benefit coverage for both active employees and retired Plan participants. The Plan’s unfunded benefit obligation of $ 3,921 and $ 3,577 as of December 31, 2015 and 2014 , respectively, is included in accounts payable and accrued expenses in the Company’s consolidated balance sheets. Net periodic benefit costs of $ 400 , $ 400 and $ 571 for the years ended December 31, 2015 , 2014 and 2013 , respectively, are included in employee benefits expense in the Company’s consolidated statements of income. Weighted average actuarial assumptions used to determine the postretirement benefit obligation at December 31, 2015 , and the net periodic benefit costs for the year then ended, included a discount rate of 3.6% and a 6.0% annual increase in the per capita cost of covered healthcare benefits. Weighted average actuarial assumptions used to determine the postretirement benefit obligation at December 31, 2014 , and the net periodic benefit costs for the year then ended, included a discount rate of 3.6% and a 6.5% annual increase in the per capita cost of covered healthcare benefits.The estimated effect of a one percent increase or a one percent decrease in the assumed healthcare cost trend rate would not significantly impact the service and interest cost components of the net periodic benefit cost or the accumulated postretirement benefit obligation. Future benefit payments are expected to be $ 163 , $ 194 , $ 219 , $ 254 , $ 295 and $ 1,500 for 2016 , 2017 , 2018 , 2019 , 2020 , and 2021 through 2025 , respectively. At December 31, 2015 , the Company had accumulated other comprehensive loss related to the Plan of $ 555 , or $ 378 net of related income tax benefit, comprised of net actuarial losses of $ 255 and an unamortized transition asset of $ 300 . The Company estimates $ 35 will be amortized from accumulated other comprehensive loss into net period benefit costs in 2016 .

Other Comprehensive Income

Other Comprehensive Income	12 Months Ended
	Dec. 31, 2015
Equity [Abstract]
Other Comprehensive Income	OTHER COMPREHENSIVE INCOME The gross amounts of each component of other comprehensive income and the related tax effects for the periods indicated are as follows: Year ended December 31, 2015 Before Tax Amount Tax Expense (Benefit) Net of Tax Amount Investment securities available-for sale: Change in net unrealized gain during period $ 5,863 $ 2,307 $ 3,556 Reclassification adjustment for net gains included in net income (137 ) (54 ) (83 ) Change in unamortized loss on available-for-sale securities transferred into held-to-maturity (1,101 ) (433 ) (668 ) Change in net unrealized gain on derivatives 165 65 100 Defined benefits post-retirement benefit plan: Change in net actuarial loss 58 23 35 Total other comprehensive income $ 4,848 $ 1,908 $ 2,940 Year ended December 31, 2014 Before Tax Amount Tax Expense (Benefit) Net of Tax Amount Investment securities available-for sale: Change in net unrealized gain during period $ 21,147 $ 8,321 $ 12,826 Reclassification adjustment for net gains included in net income (61 ) (24 ) (37 ) Unamortized premium on available-to-sale securities transferred into held-for-maturity (548 ) (216 ) (332 ) Defined benefits post-retirement benefit plan: Change in net actuarial loss 1,731 681 1,050 Total other comprehensive income $ 22,269 $ 8,762 $ 13,507 Year ended December 31, 2013 Before Tax Amount Tax Expense (Benefit) Net of Tax Amount Investment securities available-for sale: Change in net unrealized loss during period $ (52,949 ) $ (20,835 ) $ (32,114 ) Reclassification adjustment for net gains included in net income (1 ) — (1 ) Defined benefits post-retirement benefit plan: Change in net actuarial loss 137 54 83 Total other comprehensive loss $ (52,813 ) $ (20,781 ) $ (32,032 ) The components of accumulated other comprehensive income (loss), net of income taxes, are as follows: Year ended December 31, 2015 2014 Net unrealized gain (loss) on investment securities available-for-sale $ 684 $ (2,121 ) Net actuarial loss on defined benefit post-retirement benefit plans (378 ) (413 ) Net unrealized gain on derivatives 100 — Net accumulated other comprehensive income (loss) $ 406 $ (2,534 )

Non-Cash Investing and Financin

Non-Cash Investing and Financing Activities	12 Months Ended
	Dec. 31, 2015
Supplemental Cash Flow Information [Abstract]
Non-Cash Investing and Financing Activities	NON-CASH INVESTING AND FINANCING ACTIVITIES The Company transferred loans of $ 5,560 , $ 5,198 and $ 11,545 to other real estate owned in 2015 , 2014 and 2013 , respectively. The Company transferred internally originated mortgage servicing assets of $ 3,614 , $ 2,717 and $ 3,581 from loans to mortgage servicing assets in 2015 , 2014 and 2013 , respectively. During 2014 , the Company issued 1,378,230 shares of its Class A common stock valued at $35,972 as partial consideration for the acquisition of MWFC. The Company transferred real property pending disposal of $1,805 and $1,448 to other assets in 2015 and 2013 , respectively. The Company reclassified tax credit investments of $429 from held-to-maturity investment securities to other assets during 2013 .

Condensed Financial Information

Condensed Financial Information (Parent Company Only)	12 Months Ended
	Dec. 31, 2015
Condensed Financial Information of Parent Company Only Disclosure [Abstract]
Condensed Financial Information (Parent Company Only)	CONDENSED FINANCIAL INFORMATION (PARENT COMPANY ONLY) Following is condensed financial information of First Interstate BancSystem, Inc. December 31, 2015 2014 Condensed balance sheets: Cash and cash equivalents $ 55,162 $ 65,483 Investment in subsidiaries, at equity: Bank subsidiary 975,236 936,817 Nonbank subsidiaries 1,985 1,982 Total investment in subsidiaries 977,221 938,799 Advances to subsidiaries, net 6,257 4,337 Other assets 39,668 29,335 Total assets $ 1,078,308 $ 1,037,954 Other liabilities $ 25,338 $ 26,553 Long-term debt 20,000 20,000 Subordinated debentures held by subsidiary trusts 82,477 82,477 Total liabilities 127,815 129,030 Stockholders’ equity 950,493 908,924 Total liabilities and stockholders’ equity $ 1,078,308 $ 1,037,954 Years Ended December 31, 2015 2014 2013 Condensed statements of income: Dividends from subsidiaries $ 70,000 $ 58,900 $ 71,400 Other interest income 23 42 34 Other income, primarily management fees from subsidiaries 13,207 12,166 12,809 Total income 83,230 71,108 84,243 Salaries and benefits 16,267 15,722 15,914 Interest expense 3,844 4,002 4,098 Acquisition expenses 795 4,017 — Other operating expenses, net 9,920 7,512 7,546 Total expenses 30,826 31,253 27,558 Earnings before income tax benefit 52,404 39,855 56,685 Income tax benefit (6,952 ) (6,862 ) (5,703 ) Income before undistributed earnings of subsidiaries 59,356 46,717 62,388 Undistributed earnings of subsidiaries 27,439 37,684 23,748 Net income $ 86,795 $ 84,401 $ 86,136 Years Ended December 31, 2015 2014 2013 Condensed statements of cash flows: Cash flows from operating activities: Net income $ 86,795 $ 84,401 $ 86,136 Adjustments to reconcile net income to cash provided by operating activities: Undistributed earnings of subsidiaries (27,439 ) (37,684 ) (23,748 ) Stock-based compensation expense 3,959 3,634 2,936 Tax benefits from stock-based compensation 1,443 2,193 1,898 Excess tax benefits from stock-based compensation (1,184 ) (2,205 ) (2,031 ) Other, net (11,333 ) 8,991 (5,804 ) Net cash provided by operating activities 52,241 59,330 59,387 Cash flows from investing activities: Acquisition of bank holding company, net of cash and cash equivalents received (7,207 ) (37,891 ) — Net cash used in investing activities $ (7,207 ) $ (37,891 ) $ — Years Ended December 31, 2015 2014 2013 Condensed statements of cash flows (continued): Cash flows from financing activities: Net (decrease) increase in advances from nonbank subsidiaries $ (2,021 ) $ (10,632 ) $ 6,992 Redemption of preferred stock — — (50,000 ) Repayment of long-term debt (950 ) — — Repayment of junior subordinated debentures held by subsidiary trusts — (20,439 ) — Proceeds from issuance of common stock, net of stock issuance costs 3,369 6,001 9,814 Excess tax benefits from stock-based compensation 1,184 2,205 2,031 Purchase and retirement of common stock (20,647 ) (9,739 ) (448 ) Dividends paid to common stockholders (36,290 ) (28,626 ) (17,909 ) Net cash used in financing activities (55,355 ) (61,230 ) (49,520 ) Net change in cash and cash equivalents (10,321 ) (39,791 ) 9,867 Cash and cash equivalents, beginning of year 65,483 105,274 95,407 Cash and cash equivalents, end of year $ 55,162 $ 65,483 $ 105,274 There were no noncash investing or financing activities during 2015 , 2014 or 2013 .

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2015
Fair Value Disclosures [Abstract]
Fair Value Measurements	FAIR VALUE MEASUREMENTS Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. There is a fair value hierarchy which requires an entity to maximize the use of observable inputs and minimize the use of unobservable inputs when measuring fair value. The three levels of inputs that may be used to measure fair value are as follows: • Level 1 - Quoted prices in active markets for identical assets or liabilities • Level 2 - Observable inputs other than Level 1 prices, such as quoted prices for similar assets or liabilities; quoted prices in markets that are not active; or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities • Level 3 - Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of of assets or liabilities Transfers in and out of Level 1, Level 2 and Level 3 are recognized on the actual transfer date. There were no transfers between fair value hierarchy levels during the years ended December 31, 2015 and 2014. The methodologies used by the Company in determining the fair values of each class of financial instruments are based primarily on the use of independent, market-based data to reflect a value that would be reasonably expected in an orderly transaction between market participants at the measurement date. There have been no significant changes in the valuation techniques during the periods ended December 31, 2015 and 2014. Further details on the methods used to estimate the fair value of each class of financial instruments above are discussed below: Investment Securities Available-for-Sale . The methodologies used by the Company in determining the fair values of each class of financial instruments are based primarily on the use of independent, market-based data to reflect a value that would be reasonably expected in an orderly transaction between market participants at the measurement date, and therefore as classified within Level 2 of the valuation hierarchy. The Company obtains fair value measurements for investment securities from an independent pricing service. The fair value measurements consider observable data that may include dealer quotes, market spreads, cash flows, the U.S. Treasury yield curve, live trading levels, trade execution data, market consensus prepayment speeds, credit information and the investment's terms and conditions, among other things. Vendors chosen by the Company are widely recognized vendors whose evaluations support the pricing functions of financial institutions, investment and mutual funds, and portfolio managers. The Company has documented and evaluated the pricing methodologies used by the vendors and maintains internal processes that regularly test valuations. These internal processes include obtaining and reviewing available reports on internal controls, evaluating the prices for reasonableness given market changes, obtaining and evaluating the inputs used in the model for a sample of securities, investigating anomalies and confirming determinations through discussions with the vendor. For investment securities, if needed, a broker may be utilized to determine the reported fair value. Interest Rate Swap Derivative Financial Instruments. Fair values for interest rate swap derivative financial instruments are based upon the estimated amounts to settle the contracts considering current interest rates and are calculated using discounted cash flows that are observable or that can be corroborated by observable market data and, therefore, are classified within Level 2 of the valuation hierarchy. The inputs used to determine fair value include the 3 month LIBOR forward curve to estimate variable rate cash inflows and the fed funds effective swap rate to estimate the discount rate. The estimated variable rate cash inflows are compared to the fixed rate outflows and such difference is discounted to a present value to estimate the fair value of the interest rate swaps. The change in the value of derivative assets attributable to basis risk, or the risk that offsetting investments in a hedging strategy will not experience price changes in entirely opposite directions from each other, was not significant in the reported periods. The Company also obtains and compares the reasonableness of the pricing from an independent third party. For purposes of potential valuation adjustments to our derivative positions, we evaluate the credit risk of our counterparties as well as ours. Accordingly, we have considered factors such as the likelihood of our default and the default of our counterparties, our net exposures and remaining contractual life, among other things, in determining if any fair value adjustments related to credit risk are required. The change in value of derivative assets and derivative liabilities attributable to credit risk was not significant during the reported periods. Deferred Compensation Plan. The fair values of deferred compensation plan assets are based primarily on the use of independent, market-based data to reflect a value that would be reasonably expected in an orderly transaction between market participants at the measurement date, and therefore are classified within Level 2 of the valuation hierarchy. These investments are in the same funds and purchased in the same amounts as the participants’ selected investments, which represent the underlying liabilities to plan participants. Deferred compensation plan liabilities are recorded at amounts due to participants, based on the fair value of participants’ selected investments. Financial assets and financial liabilities measured at fair value on a recurring basis are as follows: Fair Value Measurements at Reporting Date Using As of December 31, 2015 Balance Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Investment securities available-for-sale: U.S. Treasury Notes $ 3,911 $ — $ 3,911 $ — Obligations of U.S. government agencies 520,181 — 520,181 — U.S. agency mortgage-backed securities & collateralized mortgage obligations 929,046 — 929,046 — Private mortgage-backed securities 156 — 156 — Other investments 3,546 — 3,546 — Derivative assets: Interest rate swaps 953 — 953 — Derivative liabilities: Interest rate swaps 829 — 829 — Deferred compensation plan assets 10,149 — 10,149 — Deferred compensation plan liabilities 10,149 — 10,149 — Fair Value Measurements at Reporting Date Using As of December 31, 2014 Balance Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Investment securities available-for-sale: Obligations of U.S. government agencies $ 720,933 $ — $ 720,933 $ — U.S. agency mortgage-backed securities & collateralized mortgage obligations 990,666 — 990,666 — Private mortgage-backed securities 325 — 325 — Derivative assets: Interest rate swaps 61 — 61 — Derivative liabilities: Interest rate swaps 59 — 59 — Deferred compensation plan assets 10,312 — 10,312 — Deferred compensation plan liabilities 10,312 — 10,312 — Additionally, from time to time, certain assets are measured at fair value on a non-recurring basis. Adjustments to fair value generally result from the application of lower-of-cost-or-market accounting or write-downs of individual assets due to impairment. The following table presents information about the Company’s assets and liabilities measured at fair value on a non-recurring basis. Fair Value Measurements at Reporting Date Using As of December 31, 2015 Total Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Total Gains (Losses) Impaired loans $ 20,875 $ — $ — $ 20,875 $ (21,804 ) Other real estate owned 1,789 — — 1,789 (382 ) Long-lived assets to be disposed of by sale 1,506 — — 1,506 (857 ) Fair Value Measurements at Reporting Date Using As of December 31, 2014 Total Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Total Gains (Losses) Impaired loans $ 30,494 $ — $ — $ 30,494 $ (14,552 ) Other real estate owned 4,554 — — 4,554 (12,665 ) Long-lived assets to be disposed of by sale 1,083 — — 1,083 (702 ) Impaired Loans. Collateralized impaired loans are reported at the fair value of the underlying collateral if repayment is expected solely from collateral. The impaired loans are reported at fair value through specific valuation allowance allocations. In addition, when it is determined that the fair value of an impaired loan is less than the recorded investment in the loan, the carrying value of the loan is adjusted to fair value through a charge to the allowance for loan losses. Collateral values are estimated using independent appraisals and management estimates of current market conditions. As of December 31, 2015 , certain impaired loans with a carrying value of $ 42,679 were reduced by specific valuation allowance allocations of $ 11,575 and partial loan charge-offs of $ 10,229 resulting in a reported fair value of $ 20,875 . As of December 31, 2014 , certain impaired loans with a carrying value of $ 45,046 were reduced by specific valuation allowance allocations of $ 5,792 and partial loan charge-offs of $ 8,760 resulting in a reported fair value of $ 30,494 . OREO. The fair values of OREO are estimated using independent appraisals and management estimates of current market conditions. Upon initial recognition, write-downs based on the foreclosed asset's fair value at foreclosure are reported through charges to the allowance for loan losses. Periodically, the fair value of foreclosed assets is remeasured with any subsequent write-downs charged to OREO expense in the period in which they are identified. Long-lived Assets to be Disposed of by Sale. Long-lived assets to be disposed of by sale are carried at the lower of carrying value or fair value less estimated costs to sell. The fair values of long-lived assets to be disposed of by sale are based upon observable market data and management estimates of current market conditions. As of December 31, 2015 , long-lived assets to be disposed of by sale with carrying values of $ 2,363 that were reduced by write-downs of $ 857 charged to other expense resulting in a reported fair value of $ 1,506 . As of December 31, 2014 , the Company had long-lived assets to be disposed of by sale of $ 1,785 that were reduced by write-downs of $702 charged to other expense resulting in a reported fair value of $1,083 . In addition, mortgage loans held for sale are required to be measured at the lower of cost or fair value. The fair value of mortgage loans held for sale is based upon binding contracts or quotes or bids from third party investors. As of December 31, 2015 and 2014 , all mortgage loans held for sale were recorded at cost. The following table presents additional quantitative information about assets measured at fair value on a non-recurring basis and for which the Company has utilized Level 3 inputs to determine fair values: As of December 31, 2015 Fair Value Valuation Technique Unobservable Inputs Range (Weighted Average) Impaired loans $ 20,875 Appraisal Appraisal adjustment 0% - 53% (38%) Other real estate owned 1,789 Appraisal Appraisal adjustment 2% - 96% (19%) Long-lived assets to be disposed of by sale 1,506 Appraisal Appraisal adjustment 0% - 9% (6%) As of December 31, 2014 Fair Value Valuation Technique Unobservable Inputs Range (Weighted Average) Impaired loans $ 30,494 Appraisal Appraisal adjustment 0% - 51% (19%) Other real estate owned 4,554 Appraisal Appraisal adjustment 0% - 50% (15%) Long-lived assets to be disposed of by sale 1,083 Appraisal Appraisal adjustment 0% - 9% (5%) The Company is required to disclose the fair value of financial instruments for which it is practical to estimate fair value. The methodologies for estimating the fair value of financial instruments that are measured at fair value on a recurring or non-recurring basis are discussed above. The methodologies for estimating the fair value of other financial instruments are discussed below. For financial instruments bearing a variable interest rate where no credit risk exists, it is presumed that recorded book values are reasonable estimates of fair value. Financial Assets. Carrying values of cash, cash equivalents and accrued interest receivable approximate fair values due to the liquid and/or short-term nature of these instruments. Fair values for investment securities, derivative assets and deferred compensation plan assets are obtained from an independent pricing service, which considers observable data that may include dealer quotes, market spreads, cash flows, the U.S. Treasury yield curve, live trading levels, trade execution data, market consensus prepayment speeds, credit information and the investment’s terms and conditions, among other things. Fair values of fixed rate loans and variable rate loans that reprice on an infrequent basis are estimated by discounting future cash flows using current interest rates at which similar loans with similar terms would be made to borrowers of similar credit quality. Carrying values of variable rate loans that reprice frequently, and with no change in credit risk, approximate the fair values of these instruments. Financial Liabilities. The fair values of demand deposits, savings accounts, securities sold under repurchase agreements and accrued interest payable are the amounts payable on demand at the reporting date. The fair values of fixed-maturity certificates of deposit are estimated using external market rates currently offered for deposits with similar remaining maturities. The carrying values of the interest bearing demand notes to the United States Treasury are deemed an approximation of fair values due to the frequent repayment and repricing at market rates. The floating rate subordinated debenture, floating rate subordinated term loan, fixed rate notes payable, fixed rate subordinated term debt, fixed rate subordinated debentures and capital lease obligation are estimated by discounting future cash flows using current rates for advances with similar characteristics. Fair values of derivative liabilities and deferred compensation plan liabilities are obtained from an independent pricing service, which considers observable data that may include dealer quotes, market spreads, cash flows, the U.S. Treasury yield curve, live trading levels, trade execution data, market consensus prepayment speeds, credit information and the investment’s terms and conditions, among other things. Commitments to Extend Credit and Standby Letters of Credit. The fair value of commitments to extend credit and standby letters of credit, based on fees currently charged to enter into similar agreements, is not significant. A summary of the estimated fair values of financial instruments follows: ` Fair Value Measurements at Reporting Date Using As of December 31, 2015 Carrying Amount Estimated Fair Value Quoted Prices in Significant Other Significant Financial assets: Cash and cash equivalents $ 780,457 $ 780,457 $ 780,457 $ — $ — Investment securities available-for-sale 1,456,840 1,456,840 — 1,456,840 — Investment securities held-to-maturity 600,665 607,550 — 607,550 — Accrued interest receivable 27,729 27,729 — 27,729 — Mortgage servicing rights, net 15,621 31,011 — 31,011 — Net loans 5,169,379 5,128,705 — 5,107,830 20,875 Derivative assets 953 953 — 953 — Deferred compensation plan assets 10,149 10,149 — 10,149 — Total financial assets $ 8,061,793 $ 8,043,394 $ 780,457 $ 7,242,062 $ 20,875 Financial liabilities: Total deposits, excluding time deposits $ 5,957,345 $ 5,975,345 $ 5,975,345 $ — $ — Time deposits 1,131,592 1,137,289 — 1,137,289 — Securities sold under repurchase agreements 510,635 510,635 — 510,635 — Other borrowed funds 2 2 — 2 — Accrued interest payable 4,960 4,960 — 4,960 — Long-term debt 27,885 27,622 — 27,622 — Subordinated debentures held by subsidiary trusts 82,477 74,969 — 74,969 — Derivative liabilities 829 829 — 829 — Deferred compensation plan liabilities 10,149 10,149 — 10,149 — Total financial liabilities $ 7,725,874 $ 7,741,800 $ 5,975,345 $ 1,766,455 $ — Fair Value Measurements at Reporting Date Using As of December 31, 2014 Carrying Amount Estimated Fair Value Quoted Prices in Significant Other Significant Financial assets: Cash and cash equivalents $ 798,670 $ 798,670 $ 798,670 $ — $ — Investment securities available-for-sale 1,711,924 1,711,924 — 1,711,924 — Investment securities held-to-maturity 575,186 584,533 — 584,533 — Accrued interest receivable 27,063 27,063 — 27,063 — Mortgage servicing rights, net 14,038 21,434 — 21,434 — Net loans 4,823,243 4,800,725 — 4,770,231 30,494 Derivative assets 61 61 — 61 — Deferred compensation plan assets 10,312 10,312 — 10,312 — Total financial assets $ 7,960,497 $ 7,954,722 $ 798,670 $ 7,125,558 $ 30,494 Financial liabilities: Total deposits, excluding time deposits $ 5,767,992 $ 5,767,992 $ 5,767,992 $ — $ — Time deposits 1,238,220 1,244,324 — 1,244,324 — Securities sold under repurchase agreements 502,250 502,250 — 502,250 — Other borrowed funds 9 9 — 9 — Accrued interest payable 5,833 5,833 — 5,833 — Long-term debt 38,067 37,781 — 37,781 — Subordinated debentures held by subsidiary trusts 82,477 75,734 — 75,734 — Derivative liabilities 829 59 — 59 — Deferred compensation plan liabilities 10,149 10,312 — 10,312 — Total financial liabilities $ 7,645,826 $ 7,644,294 $ 5,767,992 $ 1,876,302 $ —

Related Party Transactions

Related Party Transactions	12 Months Ended
	Dec. 31, 2015
Related Party Transactions [Abstract]
Related Party Transactions	RELATED PARTY TRANSACTIONS The Company conducts banking transactions in the ordinary course of business with related parties, including directors, executive officers, shareholders and their associates, on the same terms as those prevailing at the same time for comparable transactions with unrelated persons and that do not involve more than a normal risk of collectibility or present other unfavorable features. Certain executive officers, directors and greater than 5% shareholders of the Company and certain entities and individuals related to such persons, incurred indebtedness in the form of loans, as customers, of $ 33,008 and $ 33,002 at December 31, 2015 and 2014 , respectively. During 2015 , new loans and advances on existing loans of $ 7,400 were funded and loan repayments totaled $ 7,283 . In addition, $111 of loans were removed due to changes in related parties during the year. These loans were made on substantially the same terms, including interest rates and collateral, as those prevailing at the time for comparable loans with persons not related to the Company. During 2014 , the Company repurchased an aggregate of 37,615 shares of its Class A common stock from two directors and one greater than 10% shareholder of the Company at a weighted average price of $24.96 per share. The repurchases were made in privately negotiated transactions pursuant to a stock repurchase program approved by the Company's Board of Directors in November 2013 . For additional information regarding the Company's stock repurchases, see Note 14 — Capital Stock and Dividend Restrictions. The Company leases an aircraft from an entity wholly-owned by the chairman of the Company’s Board of Directors. Under the terms of the lease, the Company pays a fee for each flight hour plus certain third party operating expenses related to the aircraft. During 2015 , 2014 and 2013 , the Company paid total fees and operating expenses of $ 332 , $ 306 and $ 309 , respectively, for its use of the aircraft. In addition, the Company leases a portion of its hanger and provides pilot services to the related entity. During 2015 , 2014 and 2013 , the Company received payments from the related entity of $ 64 , $ 77 and $ 61 , respectively, for hanger use, pilot fees and reimbursement of certain third party operating expenses related to the chairman’s personal use of the aircraft. The Company purchases services from an entity in which six directors of the Company, including the chairman and executive vice chairman of the Board of Directors, have an aggregate ownership interest of 15%, and in which one director is the chairman and two directors are members of the board of such entity. Services provided for the Company’s benefit include shareholder education and communication, strategic enterprise planning and corporate governance consultation. During 2015 , 2014 and 2013 , the Company paid $ 210 , $ 255 and $ 224 , respectively, for these services. During 2012 , the Company entered into a contract with an entity wholly-owned by a director of the Company to provide construction management and advisory services related to the construction of a bank office building. Under the terms of the agreement, the entity will receive payments equal to the lesser of a fixed price of $ 180 or 4% of the actual construction contract price, with an initial payment of $ 60 due upon execution of the agreement and the remainder due in two equal installments over a two year period. Under the terms of the contract, the Company paid the entity $60 during each of 2014 and 2013 . The Company purchases property, casualty and other insurance through an agency in which a director of the Company, whose term as a director ended in May 2013, has a controlling ownership interest. The Company paid insurance premiums to the agency of $ 764 in 2013 .

Authoritative Accounting Guidan

Authoritative Accounting Guidance	12 Months Ended
	Dec. 31, 2015
Accounting Changes and Error Corrections [Abstract]
Authoritative Accounting Guidance	AUTHORITATIVE ACCOUNTING GUIDANCE ASU 2014-04 “Receivables-Troubled Debt Restructurings by Creditors (Subtopic 310-40): Reclassification of Residential Real Estate Collateralized Consumer Mortgage Loans upon Foreclosure.” The amendments in Accounting Standards Update (" ASU") 2014-04 clarify that an in-substance repossession or foreclosures occurs, and a creditor is considered to have received physical possession of residential real estate property collateralizing a consumer mortgage loan, upon either (i) the creditor obtaining legal title to the residential real estate property upon completion of a foreclosure or (ii) the borrower conveying all interest in the residential real estate property to the creditor to satisfy the loan through completion of a deed in lieu of foreclosure or through a similar legal agreement. The amendments in ASU 2014-04 also require interim and annual disclosure of both (i) the amount of foreclosed residential real estate property held by the creditor and (ii) the recorded investment in consumer mortgage loans collateralized by residential real estate property that are in the process of foreclosure. The Company adopted the amendments in ASU 2014-04 effective January 1, 2015 using a prospective transition method. Adoption of the amendments in ASU 2014-04 did not have a material impact on the Company’s consolidated financial statements, results of operations or liquidity. ASU 2014-09 "Revenue from Contracts with Customers." The amendments in ASU 2014-09 introduce a new five-step revenue recognition model in which an entity should recognize revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. ASU 2014-09 also requires disclosures sufficient to enable users to understand the nature, amount, timing, and uncertainty of revenue and cash flows arising from contracts with customers, including qualitative and quantitative disclosures about contracts with customers, significant judgments and changes in judgments, and assets recognized from the costs to obtain or fulfill a contract. ASU 2015-14 was released in August of 2015 and the amendments defer the effective date of 2014-09 for all entities by one year. Public companies, certain not-for-profit and certain employee benefit plans should apply the guidance to annual reporting period beginning after December 15, 2017. Earlier application is permitted only as of annual reporting periods beginning after December 15, 2016. The Company is continuing to evaluate the new guidance to determine the impact it will have on its consolidated financial statements, results of operations or liquidity. ASU 2014-11 "Repurchase-to-Maturity Transactions, Repurchase Financings, and Disclosures." The amendments in ASU 2014-11 expand secured borrowing treatment for certain repurchase agreements. Under the amendments in ASU 2014-11, repurchase-to-maturity transactions and repurchase agreements executed as repurchase financing transactions are required to be accounted for as secured borrowings. ASU 2014-11 requires additional disclosures about certain transactions accounted for as a sale in which the transferor retains substantially all of the exposure to the economic return on the transferred financial assets through an agreement with the same counterparty. ASU 2014-11 also requires disclosure of the types of collateral pledged and liabilities associated with an entity's repurchase agreements, securities lending transactions and repurchase-to-maturity transactions accounted for as secured borrowings. The Company adopted the amendments in ASU 2014-11 effective January 1, 2015. The adoption did not have a material impact on the Company’s consolidated financial statements, results of operations or liquidity. ASU 2014-12 "Accounting for Share-Based Payments When the Terms of an Award Provide That a Performance Target Could be Achieved after the Requisite Service Period." ASU 2014-12 amends Accounting Standards Codification ("ASC") Topic 718, Compensation-Stock Compensation, to clarify that a performance target that affects the vesting of a share-based payment award and that could be achieved after the requisite service period should be treated as a performance condition that affects the vesting of the award. ASU 2014-12 further clarifies that the requisite service period ends when the employees can cease rendering service and still be eligible to vest in the award if the performance target is achieved. The amendments in ASU 2014-12 are effective for annual periods and interim periods within those annual periods beginning after December 15, 2015. The amendments in ASU 2014-12 may be applied prospectively to all awards granted or modified after the effective date or retrospectively to all awards with performance targets that are outstanding as of the beginning of the earliest annual period presented in the financial statements and to all new or modified awards thereafter. The amendments in ASU 2014-12 will not have a material impact on the Company’s consolidated financial statements, results of operations or liquidity. ASU 2014-14 "Classification of Certain Government-Guaranteed Mortgage Loans upon Foreclosure." ASU 2014-14 updates ASC Subtopic 310-40, Receivables-Troubled Debt Restructurings by Creditors, to require that a mortgage loan be derecognized and that a separate other receivable be recognized upon foreclosure if (i) the loan has a government guarantee that is not separable from the loan before foreclosure; (ii) at the time of foreclosure, the creditor has the intent to convey the real estate property to the guarantor and make a claim on the guarantee, and the creditor has the ability to recover under that claim; and, (iii) any amount of the claim that is determined on the basis of the fair value of the real estate is fixed at the time of foreclosure. ASU 2014-14 provides that, upon foreclosure, the separate other receivable should be measured based on the amount of the loan balance (principal and interest) expected to be recovered from the guarantor. The Company adopted the amendments in ASU 2014-14 effective January 1, 2015, using a prospective transition method. Adoption of the amendments in ASU 2014-12 did not have a material impact on the Company’s consolidated financial statements, results of operations or liquidity. ASU 2014-16 "Determining Whether the Host Contract in a Hybrid Financial Instrument Issued in the Form of a Share is More Akin to Debt or to Equity." The amendments in ASU 2014-16 clarify that an entity should consider all relevant terms and features-including the embedded derivative feature being evaluated for bifurcation-in evaluating the nature of the host contract within a hybrid financial instrument. The amendments further clarify that no single term or feature would necessarily determine the economic characteristics and risk of the host contract. Rather, the nature of the host contract depends upon the economic characteristics and risk of the entire hybrid financial instrument. The amendments in ASU 2014-16 are effective for the Company for annual periods, and interim periods within those annual periods, beginning after December 15, 2015. The effects of initially adopting the amendments in ASU 2014-16 should be applied on a modified retrospective basis to existing hybrid financial instruments issued in the form of a share as of the beginning of the fiscal year for which the amendments are effective. Retrospective application is permitted to all relevant prior periods. The amendments in ASU 2014-16 will not have a material impact on the Company’s consolidated financial statements, results of operations or liquidity. ASU 2015-02 "Amendments to the Consolidation Analysis." The amendments in ASU 2015-02 (i) modify the evaluation of whether limited partnerships and similar legal entities are variable interest entities or voting interest entities, (ii) eliminate the presumption that a general partner should consolidate a limited partnership, (iii) affect the consolidation analysis of reporting entities that are involved with variable interest entities, particularly those that have fee arrangements and related party relationships, and (iv) provide scope exceptions from consolidation guidance for reporting entities with interest in legal entities that are required to comply or operate in accordance with requirements of the Investment Company Act of 1940 for registered market funds. The amendments in ASU 2015-02 are effective for public entities for fiscal years, and interim periods within those years, beginning after December 15, 2015, with early adoption permitted. The amendments in ASU 2015-02, which may be adopted using a retrospective or modified retrospective approach, will not have a material impact on the Company’s consolidated financial statements, results of operations or liquidity. ASU 2015-03 "Simplifying the Presentation of Debt Issuance Costs." The amendments in ASU 2015-03 require that debt issuance costs related to a recognized debt liability be presented in the balance sheet as a direct deduction from the carrying amount of that debt liability, rather than as a deferred charge. The guidance in Update 2015-03 did not address presentation or subsequent measurement of debt issues costs related to line-of-credit arrangements. ASU 2015-15 addresses this gap. ASU 2015-15 adds that the SEC staff would not object to an entity deferring and presenting debt issuance costs as an asset and subsequently amortizing the deferred debt issuance costs ratably over the term of the line-of-credit arrangement, regardless of whether there are any outstanding borrowings on the line-of-credit arrangement. The amendments in ASU 2015-03 are effective for public entities for fiscal years, and interim periods within those years, beginning after December 15, 2015, and should be applied on a retrospective basis. The amendments in ASU 2015-03 will not have a material impact on the Company’s consolidated financial statements, results of operations or liquidity. ASU 2015-05 "Intangibles-Goodwill and Other Internal-Use Software." The amendments in ASU 2015-05 (i) provide guidance about whether a cloud computing arrangement includes a software license. Under the guidance in ASU 2015-05, if a cloud computing arrangement includes a software license, the customer should account for the software license element of the arrangement consistent with the acquisition of other software licenses. If a cloud computing arrangement does not include a software license, the customer should account for the arrangement as a service contract. The guidance in ASU 2015-05 does not change generally accepted accounting principles for a customer's accounting for service contracts. The amendments in ASU 2015-05 are effective for public entities for annual periods, including interim periods within those annual periods, beginning after December 15, 2015, with early adoption permitted. The amendments in ASU 2015-05 may be adopted retrospectively or prospectively to all arrangements entered into or materially modified after the effective date. Adoption of the amendments in ASU 2015-05 will not have a material impact on the Company’s consolidated financial statements, results of operations or liquidity. ASU 2015-10 "Technical Corrections and Improvements." The amendments in ASU 2015-10 represent changes to clarify the codification, correct unintended application of guidance, or make minor improvements to the codification that are not expected to have a significant effect on current accounting practice or create a significant administrative cost to most entities. The amendments in ASU 2015-10 that require transition guidance are effective for all entities for fiscal years, and interim periods within those years, beginning after December 15, 2015, with early adoption permitted. All other amendments in ASU 2015-10 became effective in June 2015. The amendments in ASU 2015-03 will not have a material impact on the Company’s consolidated financial statements, results of operations or liquidity. ASU 2015-16 “Business Combinations-Simplifying the Accounting for Measurement-Period Adjustments.” The amendments in ASU 2015-16 eliminate the requirement to retrospectively account for adjustments made to provisional amounts recognized as part of a business combination. Under the amendments in ASU 2015-16, an acquirer must recognize adjustments to the provisional amounts that are identified during the measurement period in the reporting period in which the adjustment amounts are determined. The amendments in ASU 2015-16 require that the acquirer record, in the same period’s financial statements, the effect on earnings of changes in depreciation, amortization or other income effects, if any, as a result of the change to the provisional amounts, calculated as if the accounting had been completed at the acquisition date. ASU 2015-16 is effective for the Company for fiscal years beginning after December 15, 2015, including interim periods within those fiscal years. The amendments in ASU 2015-16, which are applied prospectively to adjustments to provisional amounts that occur after the effective date, will not have a material impact on the Company’s consolidated financial statements, results of operations or liquidity. ASU 2016-01 "Financial Instruments-Overall: Recognition and Measurement of Financial Assets and Financial Liabilities." ASU 2016-1, among other things, (i) requires equity investments, with certain exceptions, to be measured at fair value with changes in fair value recognized in net income, (ii) simplifies the impairment assessment of equity investments without readily determinable fair values by requiring a qualitative assessment to identify impairment, (iii) eliminates the requirement for public business entities to disclose the methods and significant assumptions used to estimate the fair value that is required to be disclosed for financial instruments measured at amortized cost on the balance sheet, (iv) requires public business entities to use the exit price notion when measuring the fair value of financial instruments for disclosure purposes, (v) requires an entity to present separately in other comprehensive income the portion of the total change in the fair value of a liability resulting from a change in the instrument-specific credit risk when the entity has elected to measure the liability at fair value in accordance with the fair value option for financial instruments, (vi) requires separate presentation of financial assets and financial liabilities by measurement category and form of financial asset on the balance sheet or the accompanying notes to the financial statements and (viii) clarifies that an entity should evaluate the need for a valuation allowance on a deferred tax asset related to available-for-sale investment securities. ASU 2016-1 will be effective for the Company on January 1, 2018 and is not expected to have a significant impact on the Company’s consolidated financial statements, results of operations or liquidity. ASU 2016-02 "Leases (Topic 842)." On February 25, 2016, the Financial Accounting Standards Board issued new lease accounting guidance in ASU No. 2016-02. Under the new guidance, lessees will be required to recognize a lease liability and a right of use asset for all leases (with the exception of short-term leases) at the commencement date of the lease and disclose key information about leasing arrangements. Accounting by lessors is largely unchanged. ASU 2016-02 will be effective for the Company on January 1, 2019 and will be applied on a modified retrospective basis. The Company is evaluating the effects of ASU 2016-02, but does not expect its adoption to have a significant impact on the Company’s consolidated financial statements, results of operations or liquidity.

Subsequent Events

Subsequent Events	12 Months Ended
	Dec. 31, 2015
Subsequent Events [Abstract]
Subsequent Events	SUBSEQUENT EVENTS Subsequent events have been evaluated for potential recognition and disclosure through the date financial statements were filed with the Securities and Exchange Commission. On January 21, 2016 , the Company declared a quarterly dividend to common shareholders of $0.22 per share, paid on February 12, 2016 to shareholders of record as of February 1, 2016 . No other events requiring recognition or disclosure were identified.

Summary of Significant Accoun37

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2015
Accounting Policies [Abstract]
Consolidation Policy	Basis of Presentation . The Company’s consolidated financial statements include the accounts of the Parent Company and its operating subsidiaries. As of December 31, 2015 , the Company had one significant subsidiary, First Interstate Bank (“FIB”). All significant intercompany balances and transactions have been eliminated in consolidation. Certain reclassifications, none of which were material, have been made in the consolidated financial statements for 2014 and 2013 to conform to the 2015 presentation. These reclassifications did not change previously reported net income or stockholders’ equity. Equity Method Investments. The Company has investments in real estate joint ventures that are not consolidated because the Company does not own a majority voting interest, control the operations or receive a majority of the losses or earnings of the joint venture. These joint ventures are accounted for using the equity method of accounting whereby the Company initially records its investment at cost (or fair value at the date of acquisition) and then subsequently adjusts the carrying value for the Company’s proportionate share of distributions and earnings or losses of the joint ventures. Variable Interest Entities. The Company’s wholly-owned business trusts, FI Statutory Trust I (“Trust I”), FI Capital Trust II (“Trust II”), FI Statutory Trust III (“Trust III”), FI Capital Trust IV (“Trust IV”), FI Statutory Trust V (“Trust V”) and FI Statutory Trust VI (“Trust VI”) are variable interest entities for which the Company is not a primary beneficiary. Accordingly, the accounts of Trust I, Trust II, Trust III, Trust IV, Trust V and Trust VI are not included in the accompanying consolidated financial statements, and are instead accounted for using the equity method of accounting. The Company has equity investments in variable interest Certified Development Entities (“CDEs”) which have received allocations under the New Markets Tax Credits Program. The underlying activities of the CDEs are community development projects designed primarily to promote community welfare, such as economic rehabilitation and development of low-income areas by providing housing, services, or jobs for residents. The maximum exposure to loss in the CDEs is the amount of equity invested and credit extended by the Company. The Company has credit protection in the form of indemnification agreements, guarantees, and collateral arrangements. As the primary beneficiary of these variable interest entities, the Company’s consolidated financial statements include the assets, liabilities, and results of operations of the CDEs. The primary activities of the CDEs are recognized in interest and fees on loans, other non-interest income and long-term debt interest expense on the Company’s statements of operations. Related cash flows are recognized in loans originated, principal collected on loans and advances or repayments of long-term debt. Assets Held in Fiduciary or Agency Capacity. The Company holds certain trust assets in a fiduciary or agency capacity. The Company also purchases and sells federal funds as an agent. These and other assets held in an agency or fiduciary capacity are not assets of the Company and, accordingly, are not included in the accompanying consolidated financial statements.
Use of Estimates	Use of Estimates. The preparation of consolidated financial statements in conformity with accounting principles generally accepted in the United States of America requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and the disclosure of contingent assets and liabilities at the date of the financial statements and income and expenses during the reporting period. Actual results could differ from those estimates. Material estimates that are particularly susceptible to change relate to the determination of the allowance for loan losses, the valuation of goodwill, fair valuations of investment securities and other financial instruments and the status of loss contingencies.
Cash and Cash Equivalents	Cash and Cash Equivalents . For purposes of reporting cash flows, cash and cash equivalents include cash on hand, amounts due from banks, federal funds sold for one day periods and interest bearing deposits in banks with original maturities of less than three months. As of December 31, 2015 and 2014 , the Company had cash of $636,345 and $631,562 , respectively, on deposit with the Federal Reserve Bank. In addition, the Company maintained compensating balances with the Federal Reserve Bank of approximately $10,031 and $7,507 as of December 31, 2015 and 2014 , respectively, to reduce service charges for check clearing services.
Investment Securities	Investment Securities . Investments in debt securities that the Company has the positive intent and ability to hold to maturity are classified as held-to-maturity and carried at amortized cost. Investments in debt securities that may be sold in response to or in anticipation of changes in interest rates and resulting prepayment risk, or other factors, and marketable equity securities are classified as available-for-sale and carried at fair value. The unrealized gains and losses on these securities are reported, net of applicable income taxes, as a separate component of stockholders’ equity and comprehensive income. Management determines the appropriate classification of securities at the time of purchase and at each reporting date management reassesses the appropriateness of the classification. The amortized cost of debt securities classified as held-to-maturity or available-for-sale is adjusted for accretion of discounts to maturity and amortization of premiums over the estimated average life of the security, or in the case of callable securities, through the first call date, using the effective yield method. Such amortization and accretion is included in interest income. Realized gains and losses are included in investment securities gains (losses). Declines in the fair value of securities below their cost that are judged to be other-than-temporary are included in other expenses if the decline is related to credit losses. Other-than-temporary impairment losses related to other factors are recognized in other comprehensive income, net of income taxes. In estimating other-than-temporary impairment losses, the Company considers, among other things, the length of time and the extent to which the fair value has been less than cost, the financial condition and near-term prospects of the issuer and the intent and ability of the Company to retain its investment in the issuer for a period of time sufficient to allow for any anticipated recovery in fair value. The cost of securities sold is based on the specific identification method.
Loans and Allowance for Loan Losses	Loans . Loans are reported at the principal amount outstanding. Interest income on loans is calculated using the simple interest method on the daily balance of the principal amount outstanding. Loan origination fees and certain direct origination costs are deferred, and the net amount is amortized as an adjustment of the related loan’s yield using a level yield method over the expected lives of the related loans. The accrual of interest on loans is discontinued when, in management’s opinion, the borrower may be unable to meet payment obligations as they become due or when a loan becomes contractually past due ninety days or more with respect to interest or principal, unless such past due loan is well secured and in the process of collection. When interest accrual is discontinued, all unpaid accrued interest is reversed against current period interest income. Interest income is subsequently recognized only to the extent cash payments are received in excess of principal due. Loans are returned to accrual status when all principal and interest amounts contractually due are brought current and when, in the opinion of management, the loans are estimated to be fully collectible as to both principal and interest. A loan is considered impaired when, based upon current information and events, it is probable that the Company will be unable to collect, on a timely basis, all amounts due according to the contractual terms of the loan’s original agreement. The amount of the impairment is measured using cash flows discounted at the loan’s effective interest rate, except when it is determined that the primary source of repayment for the loan is the operation or liquidation of the underlying collateral. In such cases, the current fair value of the collateral, reduced by anticipated selling costs, is used to measure impairment. The Company considers impaired loans to include all loans, except consumer loans, that are risk rated as doubtful or on which interest accrual has been discontinued or that have been renegotiated in a troubled debt restructuring. Interest payments received on impaired loans are applied based on whether they are on accrual or non-accrual status. Interest income recognized by the Company on impaired loans primarily relates to loans modified in troubled debt restructurings that remain on accrual status. Interest payments received on non-accrual impaired loans are applied to principal. Interest income is subsequently recognized only to the extent cash payments are received in excess of principal due. Loans acquired through the completion of a transfer, including loans acquired in business combinations, that have evidence of deterioration of credit quality since origination and for which it is probable, at acquisition, that the Company will be unable to collect all contractually required payments receivable are initially recorded at fair value (as determined by the present value of expected future cash flows) with no valuation allowance. The difference between the undiscounted cash flows expected at acquisition and the recorded fair value of the loan, or the “accretable yield,” is recognized as interest income on a level-yield method over the life of the loan. Contractually required payments for interest and principal that exceed the undiscounted cash flows expected at acquisition, or the “nonaccretable difference,” are not recognized as a yield adjustment, a loss accrual or a valuation allowance. Increases in expected cash flows subsequent to the initial investment are recognized prospectively through adjustment of the yield on the loan over its remaining life. Decreases in expected cash flows are recognized as impairment. Valuation allowances on these impaired loans reflect only losses incurred after the acquisition. A loan is considered a troubled debt restructuring when a borrower is experiencing financial difficulties that leads to a restructuring of the loan and the Company grants concessions to the borrower in the restructuring that it would not otherwise consider. These concessions may include rate reductions, principal forgiveness, extension of maturity date and other actions to minimize potential losses. Certain troubled debt restructurings are on non-accrual status at the time of restructuring and are returned to accrual status only after considering the borrower's sustained repayment performance in accordance with the restructuring agreement for a reasonable period of at least six months and management is reasonably assured of future performance. If the troubled debt restructuring meets these performance criteria and the interest rate granted at the modification is equal to or greater than the rate that the Company was willing to accept at the time of the restructuring for a new loan with comparable risk, then the loan will no longer be disclosed as a troubled debt restructuring although they continue to be individually evaluated for impairment and disclosed as impaired loans. Included in loans are certain residential mortgage loans originated for sale. These loans are carried at the lower of aggregate cost or estimated market value. Market value is estimated based on binding contracts or quotes or bids from third party investors. Residential mortgages held for sale were $52,875 and $40,828 as of December 31, 2015 and 2014 , respectively. Gains and losses on sales of mortgage loans are determined using the specific identification method and are included in income from the origination and sale of loans. As of December 31, 2015, the Company had no recorded investments in consumer mortgage loans secured by residential real estate for which formal foreclosure proceedings were in process. Allowance for Loan Losses . The allowance for loan losses is established through a provision for loan losses which is charged to expense. Loans, or portions thereof, are charged against the allowance for loan losses when management believes that the collectibility of the principal is unlikely or, with respect to consumer installment and credit card loans, according to established delinquency schedules. The allowance balance is an amount that management believes will be adequate to absorb known and inherent losses in the loan portfolio based upon quarterly analyses of the current risk characteristics of the loan portfolio, an assessment of individual problem loans and actual loss experience, industry concentrations and current economic factors and the estimated impact of current economic and environmental conditions on historical loss rates. Loans acquired in business combinations are recorded at their estimated fair values on the date of acquisition. Accordingly, no allowance for loan losses related to these loans is recorded at the date of transfer. An allowance for loan losses is recorded for credit deterioration occurring subsequent to the transfer date, if any.
Goodwill and Core Deposit Intangibles	Goodwill . The excess purchase price over the fair value of net assets from acquisitions, or goodwill, is evaluated for impairment at least annually and on an interim basis if an event or circumstance indicates that it is likely impairment has occurred. Goodwill impairment is determined by comparing the fair value of a reporting unit to its carrying amount. In any given year the Company may elect to perform a qualitative assessment to determine whether it is more likely than not that the fair value of a reporting unit is in excess of its carrying value. If it is not more likely than not that the fair value of the reporting unit is in excess of the carrying value, or if the Company elects to bypass the qualitative assessment, a two-step quantitative impairment test is performed. In performing a quantitative test for impairment, the fair value of net assets is estimated based on analyses of the Company's market value, discounted cash flows and peer values. The determination of goodwill impairment is sensitive to market-based economics and other key assumptions used in determining or allocating fair value. Variability in the market and changes in assumptions or subjective measurements used to allocate fair value are reasonably possible and may have a material impact on our consolidated financial statements or results of operations. Core Deposit Intangibles. Core deposit intangibles represent the intangible value of depositor relationships resulting from deposit liabilities assumed and are amortized using an accelerated method based on the estimated weighted average useful lives of the related deposits. Accumulated core deposit intangibles amortization was $28,040 as of December 31, 2015 and $24,652 as of December 31, 2014 . Amortization expense related to core deposit intangibles recorded as of December 31, 2015 is expected to total $ 3,220 , $ 1,933 , $ 1,414 , $ 1,201 , $ 988 , and $ 1,833 in 2016 , 2017 , 2018 , 2019 , 2020 , and thereafter, respectively.
Mortgage Servicing Rights	Mortgage Servicing Rights . The Company recognizes the rights to service mortgage loans for others, whether acquired or internally originated. Mortgage servicing rights are initially recorded at fair value based on comparable market data and are amortized in proportion to and over the period of estimated net servicing income. Mortgage servicing rights are evaluated quarterly for impairment by discounting the expected future cash flows, taking into consideration the estimated level of prepayments based on current industry expectations and the predominant risk characteristics of the underlying loans including loan type, note rate and loan term. Impairment adjustments, if any, are recorded through a valuation allowance.
Premises and Equipment	Premises and Equipment . Buildings, furniture and equipment are stated at cost less accumulated depreciation. Depreciation expense is computed using straight-line methods over estimated useful lives of 5 to 45 years for buildings and improvements and 4 to 15 years for furniture and equipment. Leasehold improvements and assets acquired under capital lease are amortized over the shorter of their estimated useful lives or the terms of the related leases. Land is recorded at cost.
Company-Owned Life Insurance	Company-Owned Life Insurance . Key executive and group life insurance policies are recorded at their cash surrender value. Separate account group life insurance policies are subject to a stable value contract that offsets the impact of interest rate fluctuations on the market value of the policies and are recorded at the stabilized investment value. Increases in the cash surrender or stabilized investment value of insurance policies, as well as insurance proceeds received, are recorded as other non-interest income, and are not subject to income taxes.
Deferred Compensation Plan	Deferred Compensation Plan. The Company has a deferred compensation plan for the benefit of certain highly compensated officers and directors of the Company. The plan allows for discretionary employer contributions in excess of tax limits applicable to the Company's 401(k) and profit sharing plans and the deferral of salary, short-term incentives or director fees subject to certain limitations. Deferred compensation plan assets and liabilities are included in the Company's consolidated balance sheets at fair value. Deferred compensation plan income or expense, consisting solely of net realized and unrealized holding gains and losses on deferred compensation plan assets, is recorded as other income in the Company’s consolidated statements of income. The corresponding net realized and unrealized holding gains and losses on deferred compensation plan liabilities is offset against employee benefits expense. As of December 31, 2015 and 2014, deferred compensation plan assets were $10,149 and $10,312, respectively. Corresponding deferred compensation plan liabilities were $10,149 and $10,136 as of December 31, 2015 and 2014, respectively. During 2015, net realized and unrealized holding losses on deferred compensation plan assets of $585 were included in other non-interest income and employee benefits expense in the Company's consolidated statements of income. During 2014, net realized and unrealized holding gains on deferred compensation plan assets of $434 were included in other non-interest income and employee benefits expense in the Company's consolidated statements of income.
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets. Long-lived assets, including premises and equipment and certain identifiable intangibles, are reviewed for impairment whenever events or changes in circumstances indicate the carrying amount of an asset may not be recoverable. The amount of the impairment loss, if any, is based on the asset’s fair value. Impairment losses of $ 806 , $102 and $616 were recognized in other non-interest expense in 2015 , 2014 and 2013 , respectively.
Other Real Estate Owned	Other Real Estate Owned . Real estate acquired in satisfaction of loans is initially carried at current fair value less estimated selling costs. Any excess of loan carrying value over the fair value of the real estate acquired is recorded as a charge to the allowance for loan losses. Subsequent declines in fair value less estimated selling costs are included in OREO expense. Subsequent increases in fair value less estimated selling costs are recorded as a reduction in OREO expense to the extent of recognized losses. Operating expenses, net of related income, and gains or losses on sales are included in OREO expense. Write-downs of $207 , $224 and $3,512 were recorded in 2015 , 2014 and 2013 , respectively. The carrying value of foreclosed residential real estate properties included in other real estate owned was $1,686 as of December 31, 2015, and $2,644 as of December 31, 2014.
Restricted Equity Securities	Restricted Equity Securities. The Company, as a member of the Federal Reserve Bank and the Federal Home Loan Bank (“FHLB”), is required to maintain investments in each of the organization’s capital stock. As of December 31, 2015 , restricted equity securities of the Federal Reserve Bank and the Federal Home Loan Bank of $ 16,421 and $ 10,135 , respectively, were included in other assets at cost. As of December 31, 2014 , restricted equity securities of the Federal Reserve Bank and the Federal Home Loan Bank were $ 16,187 and $ 10,662 , respectively. No ready market exists for these restricted equity securities, and they have no quoted market values. Restricted equity securities are periodically reviewed for impairment based on ultimate recovery of par value. The determination of whether a decline affects the ultimate recovery of par value is influenced by the significance of the decline compared to the cost basis of the restricted equity securities, the length of time a decline has persisted, the impact of legislative and regulatory changes on the issuing organizations and the liquidity positions of the issuing organizations. Based on management’s assessment, no impairment losses were recorded on restricted equity securities during 2015 , 2014 or 2013 .
Derivatives and Hedging Activities	Derivatives and Hedging Activities. For asset and liability management purposes, the Company has entered into interest rate swap contracts to hedge against changes in forecasted cash flows due to interest rate exposures. Interest rate swaps are contracts in which a series of interest payments are exchanged over a prescribed period. The notional amount upon which the interest payments are based is not exchanged. The swap agreements are derivative instruments and convert a portion of the Company’s forecasted variable rate debt to a fixed rate (i.e., cash flow hedge) over the payment term of the interest rate swap. The effective portion of the gain or loss on cash flow hedging instruments is initially reported as a component of other comprehensive income and subsequently reclassified into earnings in the same period during which the transaction affects earnings. The ineffective portion of the gain or loss on derivative instruments, if any, is recognized in earnings. The Company does not enter into interest rate swap agreements for trading or speculative purposes. The Company also enters into certain interest rate swap contracts that are not designated as hedging instruments. These derivative contracts relate to transactions in which the Company enters into an interest rate swap with a customer while at the same time entering into an offsetting interest rate swap with a third party financial institution. Because the Company acts as an intermediary for the customer, changes in the fair value of the underlying derivative contracts for the most part offset each other and do not significantly impact the Company's results of operations. The Company has residential real estate derivatives for commitments to fund certain residential real estate loans (interest rate locks) to be sold into the secondary market and forward commitments for the future delivery of residential real estate loans to third party investors on a mandatory or best efforts basis. It is the Company’s practice to enter into forward commitments for the future delivery of residential real estate loans when interest rate lock commitments are entered into in order to economically hedge the effect of changes in interest rates resulting from its commitments to fund the loans.
Income From Fiduciary Activities	Income from Fiduciary Activities . Consistent with industry practice, income for trust services is recognized on the basis of cash received. However, use of this method in lieu of accrual basis accounting does not materially affect reported earnings.
Earnings Per Common Share	Earnings Per Common Share . Basic and diluted earnings per common share are calculated using a two-class method. Under the two-class method, basic earnings per common share is calculated by dividing net income available to common shareholders by the weighted average number of common shares outstanding during the period, excluding outstanding participating securities. Participating securities include non-vested performance restricted stock awards granted prior to 2014 and all non-vested time restricted stock awards. Diluted earnings per common share is calculated by dividing net income available to common shareholders by the weighted average number of common shares outstanding determined for the basic earnings per share calculation plus the dilutive effect of stock compensation using the treasury stock method.
Income Taxes	Income Taxes . The Parent Company and its subsidiaries have elected to be included in a consolidated federal income tax return. For state income tax purposes, the combined taxable income of the Parent Company and its subsidiaries is apportioned among the states in which operations take place. Federal and state income taxes attributable to the subsidiaries, computed on a separate return basis, are paid to or received from the Parent Company. The Company accounts for income taxes using the liability method. Under the liability method, deferred tax assets and liabilities are determined based on enacted income tax rates which will be in effect when the differences between the financial statement carrying values and tax bases of existing assets and liabilities are expected to be reported in taxable income. Positions taken in the Company’s tax returns may be subject to challenge by the taxing authorities upon examination. Uncertain tax positions are initially recognized in the financial statements when it is more likely than not the position will be sustained upon examination by the tax authorities. Such tax positions are both initially and subsequently measured as the largest amount of tax benefit that is greater than 50% likely of being realized upon settlement with the tax authority, assuming full knowledge of the position and all relevant facts. The Company provides for interest and, in some cases, penalties on tax positions that may be challenged by the taxing authorities. Interest expense is recognized beginning in the first period that such interest would begin accruing. Penalties are recognized in the period that the Company claims the position in the tax return. Interest and penalties on income tax uncertainties are classified within income tax expense in the income statement. With few exceptions, the Company is no longer subject to U.S. federal and state examinations by tax authorities for years before 2012. The Company had accrued interest of $235, $206 and $176 as of December 31, 2015 , 2014 or 2013 . The Company had no penalties as of December 31, 2015 , 2014 or 2013 .
Comprehensive Income	Comprehensive Income. Comprehensive income includes net income, as well as other changes in stockholders’ equity that result from transactions and economic events other than those with shareholders. In addition to net income, the Company’s comprehensive income includes the after tax effect of changes in unrealized gains and losses on available-for-sale investment securities and derivatives designated as cash flow hedges, changes in the unamortized gain or loss on available-for-sale investment securities transferred to held-to-maturity and changes in net actuarial gains and losses on defined benefit post-retirement benefits plans
Segment Reporting	Segment Reporting. An operating segment is defined as a component of a business for which separate financial information is available that is evaluated regularly by the chief operating decision maker in deciding how to allocate resources and evaluate performance. The Company has one operating segment, community banking, which encompasses commercial and consumer banking services offered to individuals, businesses, municipalities and other entities.
Advertising Costs	Advertising Costs. Advertising costs are expensed as incurred. Advertising expense was $3,452 , $3,734 , and $3,532 in 2015 , 2014 and 2013 , respectively.
Transfers of Financial Assets	Transfers of Financial Assets. Transfers of financial assets are accounted for as sales when control over the assets has been surrendered. Control over transferred assets is deemed to be surrendered when the assets have been isolated from the Company; the transferee obtains the right, free of conditions that constrain it from taking advantage of that right, to pledge or exchange the transferred assets; and, the Company does not maintain effective control over the transferred assets through an agreement to repurchase them before their maturity.
Stock-Based Compensation	Stock-Based Compensation . Compensation cost for all stock-based awards is measured at fair value on the date of grant and is recognized over the requisite service period for awards expected to vest. Stock-based compensation expense of $ 3,959 , $ 3,634 and $ 2,936 for the years ended December 31, 2015 , 2014 and 2013 , respectively, is included in benefits expense in the Company’s consolidated statements of income. Related income tax benefits recognized for the years ended December 31, 2015 , 2014 and 2013 were $ 1,443 , $ 1,390 and $ 1,122 , respectively.
Fair Value of Financial Instruments, Policy	Fair Value Measurements. In general, fair value measurements are based upon quoted market prices, where available. If quoted market prices are not available, fair value measurements are estimated using relevant market information and other assumptions. Fair value estimates involve uncertainties and require some degree of judgment regarding interest rates, credit risk, prepayments and other factors. The use of different assumptions or estimation techniques may have a significant effect on the fair value amounts reported.

Acquisitions (Tables)

Acquisitions (Tables)	12 Months Ended
	Dec. 31, 2015
Business Acquisition [Line Items]
Schedule of Recognized Identifiable Assets Acquired and Liabilities Assumed	Absarokee MWFC July 24, 2015 July 31, 2014 Assets acquired: Cash and cash equivalents $ 5,598 $ 74,035 Investment securities 27,574 104,911 Loans 36,644 360,272 Allowance for loan losses — — Premises and equipment 3,128 29,436 Company-owned life insurance — 13,046 Core deposit intangible assets 695 11,014 Other assets 898 18,885 Total assets acquired 74,537 611,599 Liabilities assumed: Deposits 63,565 515,379 Repurchase agreements 2,000 — Long term debt 1,253 — Subordinated debentures held by subsidiary trusts — 20,439 Other liabilities 633 23,231 Total liabilities assumed 67,451 559,049 Net assets acquired 7,086 52,550 Consideration paid: Cash 7,234 38,479 Class A common stock — 35,972 Total consideration paid 7,234 74,451 Goodwill $ 148 $ 21,901
Business Acquisition, Pro Forma Information	The following table presents unaudited pro forma consolidated revenues and net income as if the MWFC acquisition had occurred as of January 1, 2013. Year ended December 31, (unaudited) 2014 2013 Interest income $ 280,102 $ 280,455 Non-interest income 114,984 120,005 Total revenues $ 395,086 $ 400,460 Net income $ 87,129 $ 84,264

Investment Securities (Tables)

Investment Securities (Tables)	12 Months Ended
	Dec. 31, 2015
Investments, Debt and Equity Securities [Abstract]
Amortized Cost and Approximate Fair Values of Investment Securities	The amortized cost and approximate fair values of investment securities are summarized as follows: December 31, 2015 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Estimated Fair Value Available-for-Sale U.S. Treasury notes $ 3,912 $ 3 $ (4 ) $ 3,911 Obligations of U.S. government agencies 521,079 712 (1,610 ) 520,181 U.S. agency residential mortgage-backed securities & collateralized mortgage obligations 921,699 9,448 (2,101 ) 929,046 Private mortgage-backed securities 156 1 (1 ) 156 Other investments 3,550 5 (9 ) 3,546 Total $ 1,450,396 $ 10,169 $ (3,725 ) $ 1,456,840 December 31, 2015 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Estimated Fair Value Held-to Maturity State, county and municipal securities $ 173,785 $ 5,103 $ (227 ) $ 178,661 Corporate securities 50,046 64 (220 ) 49,890 U.S agency residential mortgage-backed securities & 376,480 7,686 (5,522 ) 378,644 Other investments 354 1 — 355 Total $ 600,665 $ 12,854 $ (5,969 ) $ 607,550 Gross gains of $ 156 and gross losses of $ 19 were realized on the disposition of available-for-sale securities in 2015 . December 31, 2014 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Estimated Fair Value Available-for-Sale Obligations of U.S. government agencies $ 725,408 $ 895 $ (5,370 ) $ 720,933 U.S. agency residential mortgage-backed securities & collateralized mortgage obligations 982,764 11,526 (3,624 ) 990,666 Private mortgage-backed securities 322 5 (2 ) 325 Total $ 1,708,494 $ 12,426 $ (8,996 ) $ 1,711,924 December 31, 2014 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Estimated Fair Value Held-to Maturity State, county and municipal securities $ 188,941 $ 5,949 $ (386 ) $ 194,504 Corporate securities 32,565 54 (75 ) 32,544 U.S. agency residential mortgage-backed securities & collateralized mortgage obligations 353,176 5,563 (1,758 ) 356,981 Other securities 504 — — 504 Total $ 575,186 $ 11,566 $ (2,219 ) $ 584,533
Gross Unrealized Losses and Fair Values of Investment Securities	The following tables show the gross unrealized losses and fair values of investment securities, aggregated by investment category, and the length of time individual investment securities have been in a continuous unrealized loss position, as of December 31, 2015 and 2014 . Less than 12 Months 12 Months or More Total December 31, 2015 Fair Value Gross Unrealized Losses Fair Value Gross Unrealized Losses Fair Value Gross Unrealized Losses Available-for-Sale U.S. Treasury notes $ 2,092 $ (4 ) $ — $ — $ 2,092 $ (4 ) Obligations of U.S. government agencies 209,631 (1,077 ) 54,619 (533 ) 264,250 (1,610 ) U.S. agency residential mortgage-backed securities & collateralized mortgage obligations 343,875 (1,577 ) 28,010 (524 ) 371,885 (2,101 ) Private mortgage-backed securities — — 61 (1 ) 61 (1 ) Other investments 1,225 (9 ) — — 1,225 (9 ) Total $ 556,823 $ (2,667 ) $ 82,690 $ (1,058 ) $ 639,513 $ (3,725 ) Less than 12 Months 12 Months or More Total December 31, 2015 Fair Value Gross Unrealized Losses Fair Value Gross Unrealized Losses Fair Value Gross Unrealized Losses Held-to-Maturity State, county and municipal securities $ 10,182 $ (39 ) $ 9,476 $ (188 ) $ 19,658 $ (227 ) U.S. agency residential mortgage-backed 87,033 (4,390 ) 69,539 (1,132 ) 156,572 (5,522 ) Corporate securities 31,135 (220 ) — — 31,135 (220 ) Total $ 128,350 $ (4,649 ) $ 79,015 $ (1,320 ) $ 207,365 $ (5,969 ) Less than 12 Months 12 Months or More Total December 31, 2014 Fair Value Gross Unrealized Losses Fair Value Gross Unrealized Losses Fair Value Gross Unrealized Losses Available-for-Sale Obligations of U.S. government agencies $ 135,888 $ (702 ) $ 309,283 $ (4,668 ) $ 445,171 $ (5,370 ) U.S. agency residential mortgage-backed securities & collateralized mortgage obligations 219,214 (887 ) 151,380 (2,737 ) 370,594 (3,624 ) Private mortgage-backed securities — — 90 (2 ) 90 (2 ) Total $ 355,102 $ (1,589 ) $ 460,753 $ (7,407 ) $ 815,855 $ (8,996 ) Less than 12 Months 12 Months or More Total December 31, 2014 Fair Value Gross Unrealized Losses Fair Value Gross Unrealized Losses Fair Value Gross Unrealized Losses Held-to-Maturity State, county and municipal securities $ 7,979 $ (13 ) $ 20,097 $ (373 ) $ 28,076 $ (386 ) U.S. agency residential mortgage-backed securities & collateralized mortgage obligations 61,201 (1,758 ) — — $ 61,201 $ (1,758 ) Corporate securities 14,755 (75 ) — — 14,755 (75 ) Total $ 83,935 $ (1,846 ) $ 20,097 $ (373 ) $ 104,032 $ (2,219 )
Maturities of Investment Securities	All other investment securities maturities are shown at contractual maturity dates. Available-for-Sale Held-to-Maturity December 31, 2015 Amortized Cost Estimated Fair Value Amortized Cost Estimated Fair Value Within one year $ 329,638 $ 331,620 $ 100,695 $ 101,885 After one year but within five years 1,018,573 1,022,351 320,310 322,281 After five years but within ten years 46,874 47,117 134,606 137,304 After ten years 55,311 55,752 45,054 46,080 Total $ 1,450,396 $ 1,456,840 $ 600,665 $ 607,550

Loans (Tables)

Loans (Tables)	12 Months Ended
	Dec. 31, 2015
Receivables [Abstract]
Schedule of Loans by Class	The following table presents loans by class as of the dates indicated: December 31, 2015 2014 Real estate loans: Commercial $ 1,793,258 $ 1,639,422 Construction: Land acquisition & development 224,066 220,443 Residential 111,763 96,580 Commercial 94,890 101,246 Total construction loans 430,719 418,269 Residential 1,032,851 999,903 Agricultural 156,234 167,659 Total real estate loans 3,413,062 3,225,253 Consumer: Indirect consumer 622,529 552,863 Other consumer 153,717 144,141 Credit card 68,107 65,467 Total consumer loans 844,353 762,471 Commercial 792,416 740,073 Agricultural 142,151 124,859 Other, including overdrafts 1,339 3,959 Loans held for investment 5,193,321 4,856,615 Mortgage loans held for sale 52,875 40,828 Total loans $ 5,246,196 $ 4,897,443
Deteriorated Loans Transferred in	December 31, 2015 2014 Outstanding balance $ 33,755 $ 41,910 Carrying value: Loans on accrual status 21,507 31,870 Loans on non-accrual status — — Total carrying value $ 21,507 $ 31,870 The following table summarizes changes in the accretable yield for loans acquired credit impaired for year ended December 31, 2015 and 2014 : Year Ended December 31, 2015 2014 Beginning balance $ 5,781 $ — Acquisitions 432 5,233 Accretion income (2,884 ) (735 ) Additions 594 — Reductions due to exit events (517 ) (201 ) Reclassifications from nonaccretable differences 3,307 1,484 Ending balance $ 6,713 $ 5,781
Schedule of Recorded Investment in Past Due Loans by Class	The following tables present the contractual aging of the Company’s recorded investment in past due loans by class as of the period indicated: Total Loans 30 - 59 60 - 89 > 90 30 or More Days Days Days Days Current Non-accrual Total As of December 31, 2015 Past Due Past Due Past Due Past Due Loans Loans Loans Real estate Commercial $ 6,051 $ 724 $ 418 $ 7,193 $ 1,762,294 $ 23,771 $ 1,793,258 Construction: Land acquisition & development 3,190 163 1,325 4,678 212,757 6,631 224,066 Residential 1,288 — — 1,288 110,182 293 111,763 Commercial 3,232 — — 3,232 90,703 955 94,890 Total construction loans 7,710 163 1,325 9,198 413,642 7,879 430,719 Residential 5,991 1,196 2,063 9,250 1,018,359 5,242 1,032,851 Agricultural 176 17 — 193 150,686 5,355 156,234 Total real estate loans 19,928 2,100 3,806 25,834 3,344,981 42,247 3,413,062 Consumer: Indirect consumer 6,675 1,089 210 7,974 614,029 526 622,529 Other consumer 1,312 331 34 1,677 151,381 659 153,717 Credit card 533 317 477 1,327 66,768 12 68,107 Total consumer loans 8,520 1,737 721 10,978 832,178 1,197 844,353 Commercial 8,493 1,060 699 10,252 759,851 22,313 792,416 Agricultural 879 152 62 1,093 140,430 628 142,151 Other, including overdrafts — — 314 314 1,025 — 1,339 Loans held for investment 37,820 5,049 5,602 48,471 5,078,465 66,385 5,193,321 Mortgage loans originated for sale — — — — 52,875 — 52,875 Total loans $ 37,820 $ 5,049 $ 5,602 $ 48,471 $ 5,131,340 $ 66,385 $ 5,246,196 Total Loans 30 - 59 60 - 89 > 90 30 or More Days Days Days Days Current Non-accrual Total As of December 31, 2014 Past Due Past Due Past Due Past Due Loans Loans Loans Real estate Commercial $ 4,692 $ 1,609 $ 331 $ 6,632 $ 1,605,421 $ 27,369 $ 1,639,422 Construction: Land acquisition & development 839 383 — 1,222 210,969 8,252 220,443 Residential — 475 — 475 95,833 272 96,580 Commercial 100 — — 100 98,582 2,564 101,246 Total construction loans 939 858 — 1,797 405,384 11,088 418,269 Residential 6,969 645 1,762 9,376 987,735 2,792 999,903 Agricultural 1,624 236 — 1,860 158,957 6,842 167,659 Total real estate loans 14,224 3,348 2,093 19,665 3,157,497 48,091 3,225,253 Consumer: Indirect consumer 3,235 482 6 3,723 548,757 383 552,863 Other consumer 988 140 32 1,160 142,432 549 144,141 Credit card 369 284 315 968 64,484 15 65,467 Total consumer loans 4,592 906 353 5,851 755,673 947 762,471 Commercial 3,659 994 147 4,800 722,575 12,698 740,073 Agricultural 1,125 — — 1,125 123,288 446 124,859 Other, including overdrafts — — — — 3,959 — 3,959 Loans held for investment 23,600 5,248 2,593 31,441 4,762,992 62,182 4,856,615 Mortgage loans originated for sale — — — — 40,828 — 40,828 Total loans $ 23,600 $ 5,248 $ 2,593 $ 31,441 $ 4,803,820 $ 62,182 $ 4,897,443
Schedule of Recorded Investment in Impaired Loans	The following tables present information on the Company’s recorded investment in impaired loans as of dates indicated: December 31, 2015 Unpaid Total Principal Balance Recorded Investment With No Allowance Recorded Investment With Allowance Total Recorded Investment Related Allowance Real estate: Commercial $ 58,179 $ 27,882 $ 17,614 $ 45,496 $ 3,401 Construction: Land acquisition & development 15,503 7,245 778 8,023 282 Residential 992 293 — 293 — Commercial 1,264 340 739 1,079 739 Total construction loans 17,759 7,878 1,517 9,395 1,021 Residential 7,073 3,547 2,317 5,864 367 Agricultural 6,434 5,563 198 5,761 5 Total real estate loans 89,445 44,870 21,646 66,516 4,794 Commercial 29,593 10,744 13,727 24,471 6,487 Agricultural 1,349 622 356 978 294 Total $ 120,387 $ 56,236 $ 35,729 $ 91,965 $ 11,575 December 31, 2014 Unpaid Total Principal Balance Recorded Investment With No Allowance Recorded Investment With Allowance Total Recorded Investment Related Allowance Real estate: Commercial $ 41,603 $ 28,143 $ 11,246 $ 39,389 $ 1,608 Construction: Land acquisition & development 12,511 7,262 1,615 8,877 574 Residential 459 272 — 272 — Commercial 2,729 253 2,442 2,695 904 Total construction loans 15,699 7,787 4,057 11,844 1,478 Residential 2,959 2,452 341 2,793 143 Agricultural 8,844 6,444 2,305 8,749 732 Total real estate loans 69,105 44,826 17,949 62,775 3,961 Commercial 16,904 11,882 2,644 14,526 1,190 Agricultural 1,231 342 837 1,179 641 Total $ 87,240 $ 57,050 $ 21,430 $ 78,480 $ 5,792 December 31, 2013 Unpaid Total Principal Balance Recorded Investment With No Allowance Recorded Investment With Allowance Total Recorded Investment Related Allowance Real estate: Commercial $ 64,780 $ 29,216 $ 33,937 $ 63,153 $ 5,210 Construction: Land acquisition & development 23,906 9,901 7,226 17,127 1,434 Residential 1,816 1,095 277 1,372 26 Commercial 397 279 84 363 85 Total construction loans 26,119 11,275 7,587 18,862 1,545 Residential 9,448 5,081 967 6,048 249 Agricultural 8,895 6,429 2,370 8,799 335 Total real estate loans 109,242 52,001 44,861 96,862 7,339 Commercial 15,448 10,684 2,901 13,585 1,504 Agricultural 177 39 86 125 86 Total $ 124,867 $ 62,724 $ 47,848 $ 110,572 $ 8,929 The following tables present the average recorded investment in and income recognized on impaired loans for the periods indicated: Year Ended December 31, 2015 2014 2013 Average Recorded Investment Income Recognized Average Recorded Investment Income Recognized Average Recorded Investment Income Recognized Real estate: Commercial $ 39,233 $ 784 $ 54,701 $ 876 $ 66,330 $ 1,092 Construction: Land acquisition & development 8,337 54 13,056 43 19,523 487 Residential 282 — 822 — 1,893 — Commercial 1,887 7 1,529 8 3,936 4 Total construction loans 10,506 61 15,407 51 25,352 491 Residential 4,055 1 4,537 5 8,104 17 Agricultural 7,156 39 8,774 78 8,230 8 Total real estate loans 60,950 885 83,419 1,010 108,016 1,608 Commercial 18,502 123 13,789 50 15,047 68 Agricultural 858 26 447 23 313 16 Total $ 80,310 $ 1,034 $ 97,655 $ 1,083 $ 123,376 $ 1,692
Schedule of Loans Renegotiated in Troubled Debt Restructurings	The following table presents information on the Company's troubled debt restructurings that occurred during the periods indicated: Number of Notes Type of Concession Principal Balance at Restructure Date Year Ended December 31, 2015 Interest only period Extension of terms or maturity Interest rate adjustment Other Commercial Real Estate 2 $ — $ 628 $ — $ 54 $ 682 Indirect Consumer 1 — — — 4 4 Commercial 12 — 8,689 3,318 455 12,462 Total 15 $ — $ 9,317 $ 3,318 $ 513 $ 13,148 Number of Notes Type of Concession Principal Balance at Restructure Date Year ended December 31, 2014 Interest only period Extension of terms or maturity Interest rate adjustment Other Real estate: Commercial 13 $ 4,753 $ 672 $ 84 $ 1,047 $ 6,556 Residential 1 — — — 15 15 Total real estate loans 14 4,753 672 84 1,062 6,571 Consumer 1 — 113 — — 113 Commercial 5 476 — — 30 506 Total 20 $ 5,229 $ 785 $ 84 $ 1,092 $ 7,190 Number of Notes Type of Concession Principal Balance at Restructure Date Year ended December 31, 2013 Interest only period Extension of terms or maturity Interest rate adjustment Other Real estate: Commercial 19 $ 543 $ 1,378 $ 11,420 $ 2,310 $ 15,651 Construction: Land acquisition & development 8 528 7,308 1,952 — 9,788 Residential 3 — 408 411 — 819 Total construction loans 11 528 7,716 2,363 — 10,607 Residential 5 — 708 — 79 787 Agriculture 1 — — 188 — 188 Total real estate loans 36 1,071 9,802 13,971 2,389 27,233 Consumer 1 — — 27 — 27 Commercial 6 613 178 265 87 1,143 Total 43 $ 1,684 $ 9,980 $ 14,263 $ 2,476 $ 28,403 Other concessions include payment reductions or deferrals for a specified period of time or the extension of amortization schedules. A specific reserve may have been previously recorded for loans modified in troubled debt restructurings that were on non-accrual status or otherwise deemed impaired before the modification. In periods subsequent to modification, the Company continues to evaluate all loans modified in troubled debt restructurings for possible impairment, which is recognized through the allowance for loan losses. Financial effects of modifications may include principal loan forgiveness or other charge-offs directly related to the restructuring. The Company had no charge-offs directly related to loans modified in troubled debt restructurings taken at the time of restructuring during 2015 , 2014 or 2013 . The Company considers a payment default to occur on loans modified in troubled debt restructurings when the loan is 90 days or more past due or was placed on non-accrual status after the modification. The following table presents information on the Company's troubled debt restructurings during the previous 12 months for which there was a payment default. Year ended December 31, 2015 Number of Notes Balance Indirect Consumer 1 $ 4 Commercial 2 240 Total 3 $ 244
Schedule of Recorded Investment in Criticized Loans by Class and Credit Quality Indicator	The following tables present the Company’s recorded investment in criticized loans by class and credit quality indicator based on the most recent analysis performed as of the dates indicated: As of December 31, 2015 Other Assets Especially Mentioned Substandard Doubtful Total Criticized Loans Real estate: Commercial $ 61,787 $ 84,556 $ 10,609 $ 156,952 Construction: Land acquisition & development 16,593 12,482 591 29,666 Residential 1,640 1,886 — 3,526 Commercial 166 323 756 1,245 Total construction loans 18,399 14,691 1,347 34,437 Residential 4,453 9,661 2,540 16,654 Agricultural 6,114 16,529 — 22,643 Total real estate loans 90,753 125,437 14,496 230,686 Consumer: Indirect consumer 644 1,131 154 1,929 Other consumer 651 1,130 198 1,979 Total consumer loans 1,295 2,261 352 3,908 Commercial 32,975 27,982 15,085 76,042 Agricultural 2,247 7,105 417 9,769 Total $ 127,270 $ 162,785 $ 30,350 $ 320,405 As of December 31, 2014 Other Assets Especially Mentioned Substandard Doubtful Total Criticized Loans Real estate: Commercial $ 84,533 $ 83,448 $ 15,246 $ 183,227 Construction: Land acquisition & development 11,826 15,016 2,507 29,349 Residential 2,029 2,666 — 4,695 Commercial 39 253 2,442 2,734 Total construction loans 13,894 17,935 4,949 36,778 Residential 10,473 10,848 1,121 22,442 Agricultural 10,122 12,328 612 23,062 Total real estate loans 119,022 124,559 21,928 265,509 Consumer: Indirect consumer 916 1,590 121 2,627 Other consumer 553 1,085 432 2,070 Credit card — 348 1,263 1,611 Total consumer loans 1,469 3,023 1,816 6,308 Commercial 25,766 32,433 10,273 68,472 Agricultural 7,827 3,660 837 12,324 Total $ 154,084 $ 163,675 $ 34,854 $ 352,613

Allowance for Loan Losses (Tabl

Allowance for Loan Losses (Tables)	12 Months Ended
	Dec. 31, 2015
Receivables [Abstract]
Schedule of Allowance for Loan Losses by Portfolio Segment	The following table presents a summary of changes in the allowance for loan losses by portfolio segment: Year ended December 31, 2015 Real Estate Consumer Commercial Agriculture Other Total Allowance for loan losses: Beginning balance $ 53,884 $ 5,035 $ 14,307 $ 974 $ — $ 74,200 Provision charged (credited) to operating expense (645 ) 3,243 4,376 (152 ) — 6,822 Less loans charged-off (4,076 ) (5,683 ) (1,657 ) (221 ) — (11,637 ) Add back recoveries of loans previously charged-off 3,133 2,549 1,749 1 — 7,432 Ending balance $ 52,296 $ 5,144 $ 18,775 $ 602 $ — $ 76,817 Individually evaluated for impairment $ 4,794 $ — $ 6,487 $ 294 $ — $ 11,575 Collectively evaluated for impairment 47,502 5,144 12,288 308 — 65,242 Ending balance $ 52,296 $ 5,144 $ 18,775 $ 602 $ — $ 76,817 Total loans: Individually evaluated for impairment $ 66,516 $ — $ 24,471 $ 978 $ — $ 91,965 Collectively evaluated for impairment 3,346,546 844,353 767,945 141,173 1,339 5,101,356 Total loans held for investment $ 3,413,062 $ 844,353 $ 792,416 $ 142,151 $ 1,339 $ 5,193,321 Year ended December 31, 2014 Real Estate Consumer Commercial Agriculture Other Total Allowance for loan losses: Beginning balance $ 63,923 $ 6,193 $ 14,747 $ 476 $ — $ 85,339 Provision charged (credited) to operating expense (10,348 ) 1,382 1,809 535 — (6,622 ) Less loans charged-off (3,014 ) (4,887 ) (6,030 ) (64 ) — (13,995 ) Add back recoveries of loans previously charged-off 3,323 2,347 3,781 27 — 9,478 Ending balance $ 53,884 $ 5,035 $ 14,307 $ 974 $ — $ 74,200 Individually evaluated for impairment $ 3,961 $ — $ 1,190 $ 641 $ — $ 5,792 Collectively evaluated for impairment 49,923 5,035 13,117 333 — 68,408 Ending balance $ 53,884 $ 5,035 $ 14,307 $ 974 $ — $ 74,200 Total loans: Individually evaluated for impairment $ 62,775 $ — $ 14,526 $ 1,179 $ — $ 78,480 Collectively evaluated for impairment 3,162,478 762,471 725,547 123,680 3,959 4,778,135 Total loans held for investment $ 3,225,253 $ 762,471 $ 740,073 $ 124,859 $ 3,959 $ 4,856,615 Year ended December 31, 2013 Real Estate Consumer Commercial Agriculture Other Total Allowance for loan losses: Beginning balance $ 75,782 $ 7,141 $ 17,085 $ 503 $ — $ 100,511 Provision charged (credited) to operating expense (7,722 ) 1,605 41 (49 ) — (6,125 ) Less loans charged-off (10,224 ) (4,612 ) (5,672 ) (5 ) — (20,513 ) Add back recoveries of loans previously charged-off 6,087 2,059 3,293 27 — 11,466 Ending balance $ 63,923 $ 6,193 $ 14,747 $ 476 $ — $ 85,339 Individually evaluated for impairment $ 7,339 $ — $ 1,504 $ 86 $ — $ 8,929 Collectively evaluated for impairment 56,584 6,193 13,243 390 — 76,410 Ending balance $ 63,923 $ 6,193 $ 14,747 $ 476 $ — $ 85,339 Total loans: Individually evaluated for impairment $ 96,862 $ — $ 13,585 $ 125 $ — $ 110,572 Collectively evaluated for impairment 2,745,393 671,587 662,959 111,747 1,734 4,193,420 Total loans held for investment $ 2,842,255 $ 671,587 $ 676,544 $ 111,872 $ 1,734 $ 4,303,992

Premises and Equipment (Tables)

Premises and Equipment (Tables)	12 Months Ended
	Dec. 31, 2015
Property, Plant and Equipment [Abstract]
Premises and Equipment and Related Accumulated Depreciation	Premises and equipment and related accumulated depreciation are as follows: December 31, 2015 2014 Land $ 37,999 $ 40,620 Buildings and improvements 213,321 209,328 Furniture and equipment 81,354 74,959 332,674 324,907 Less accumulated depreciation (141,862 ) (129,695 ) Premises and equipment, net $ 190,812 $ 195,212

Company - Owned Life Insurance

Company - Owned Life Insurance (Tables)	12 Months Ended
	Dec. 31, 2015
Investments, All Other Investments [Abstract]
Schedule of Life Insurance Corporate or Bank Owned	Company-owned life insurance consists of the following: December 31, 2015 2014 Key executive, principal shareholder $ 3,926 $ 3,798 Key executive split dollar 4,778 4,707 Group life 178,549 145,316 Total $ 187,253 $ 153,821

Other Real Estate Owned (Tables

Other Real Estate Owned (Tables)	12 Months Ended
	Dec. 31, 2015
Repossessed Assets [Abstract]
Other Real Estate Owned Roll Forward	Information with respect to the Company’s other real estate owned follows: Year Ended December 31, 2015 2014 2013 Balance at beginning of year $ 13,554 $ 15,504 $ 32,571 Acquisitions — 3,608 — Additions 5,560 5,198 11,545 Capitalized improvements — — 65 Valuation adjustments (207 ) (224 ) (3,512 ) Dispositions (12,653 ) (10,532 ) (25,165 ) Balance at end of year $ 6,254 $ 13,554 $ 15,504

Derivatives and Hedging (Tables

Derivatives and Hedging (Tables)	12 Months Ended
	Dec. 31, 2015
Derivatives, Fair Value [Line Items]
Schedule of Derivative Instruments in Statement of Financial Position, Fair Value [Table Text Block]	December 31, 2015 December 31, 2014 Notional Amount Estimated Fair Value Notional Amount Estimated Fair Value Derivatives designated as hedges: Interest rate swap $ 100,000 $ 165 $ — $ — Non-hedging interest rate derivatives: Interest rate swap-assets 9,369 788 3,200 61 Interest rate swap-liabilities 9,369 829 3,200 59

Derivatives and Hedging General

Derivatives and Hedging General Discussion on Derivatives and Hedging (Tables)	12 Months Ended
	Dec. 31, 2015
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments, Gain (Loss) [Table Text Block]	As of or For The Year Ended December 31, 2015 2014 Derivatives designated as hedges: Amount of gain recognized in other comprehensive income (effective portion) $ 165 $ — Non-hedging interest rate derivatives: Amount of gain (loss) recognized in other non-interest income (43 ) 2

Mortgage Servicing Rights (Tabl

Mortgage Servicing Rights (Tables)	12 Months Ended
	Dec. 31, 2015
Transfers and Servicing [Abstract]
Schedule of Servicing Assets at Amortized Value	Information with respect to the Company’s mortgage servicing rights follows: Year Ended December 31, 2015 2014 2013 Balance at beginning of year $ 14,374 $ 14,018 $ 13,224 Acquisitions of mortgage servicing rights 306 — — Originations of mortgage servicing rights 3,614 2,717 3,581 Amortization expense (2,434 ) (2,361 ) (2,787 ) Balance at end of year 15,860 14,374 14,018 Less valuation reserve (239 ) (336 ) (472 ) Balance at end of year $ 15,621 $ 14,038 $ 13,546 Principal balance of serviced loans underlying mortgage servicing rights $ 2,906,239 $ 2,615,311 $ 2,416,621 Mortgage servicing rights as a percentage of serviced loans 0.54 % 0.54 % 0.56 %

Deposits (Tables)

Deposits (Tables)	12 Months Ended
	Dec. 31, 2015
Deposits [Abstract]
Schedule of Deposits, By Type	Deposits are summarized as follows: December 31, 2015 2014 Non-interest bearing demand $ 1,823,716 $ 1,791,364 Interest bearing: Demand 2,178,373 2,133,273 Savings 1,955,256 1,843,355 Time, $100 and over 487,372 520,125 Time, other 644,220 718,095 Total interest bearing 5,265,221 5,214,848 Total deposits $ 7,088,937 $ 7,006,212
Schedule of Maturities of Time Deposits	Maturities of time deposits at December 31, 2015 are as follows: Time, $100 and Over Total Time Due within 3 months or less $ 109,343 $ 309,819 Due after 3 months and within 6 months 82,059 161,333 Due after 6 months and within 12 months 131,381 266,174 Due after 12 months 164,589 394,266 Total $ 487,372 $ 1,131,592

Long-Term Debt and Other Borr49

Long-Term Debt and Other Borrowed Funds (Tables)	12 Months Ended
	Dec. 31, 2015
Debt Disclosure [Abstract]
Summary of Long-Term Debt	A summary of long-term debt follows: December 31, 2015 2014 Parent Company: 6.81% subordinated term loan maturing January 9, 2018, principal due at maturity, interest payable quarterly $ 20,000 $ 20,000 Subsidiaries: Variable rate subordinated term loan maturing February 28, 2018, principal due at maturity, interest payable quarterly — 15,000 4.86% note payable to FHLB, maturing October 31, 2015 — 225 8.00% capital lease obligation with term ending October 25, 2029 1,582 1,643 6.24% note payable maturing September 2032, principal due at maturity, interest payable monthly 1,343 1,199 2.28% note payable maturing July 29, 2022, principal due at maturity, interest payable monthly 4,960 — Total long-term debt $ 27,885 $ 38,067
Schedule of Maturities of Long-term Debt	Maturities of long-term debt at December 31, 2015 are as follows: 2016 $ 65 2017 71 2018 20,077 2019 83 2020 90 Thereafter 7,499 Total $ 27,885

Subordinated Debentures Held 50

Subordinated Debentures Held by Subsidiary Trusts (Tables)	12 Months Ended
	Dec. 31, 2015
Subordinated Borrowings [Abstract]
Schedule of Subordinated Borrowings	A summary of Subordinated Debenture issuances follows: Principal Amount Outstanding as of December 31, Issuance Maturity Date 2015 2014 October 2007 January 1, 2038 $ 10,310 $ 10,310 November 2007 December 15, 2037 15,464 15,464 December 2007 December 15, 2037 20,619 20,619 December 2007 April 1, 2038 15,464 15,464 January 2008 April 1, 2038 10,310 10,310 January 2008 April 1, 2038 10,310 10,310 Total subordinated debentures held by subsidiary trusts $ 82,477 $ 82,477

Earnings per Share (Tables)

Earnings per Share (Tables)	12 Months Ended
	Dec. 31, 2015
Earnings Per Share [Abstract]
Computation of Basic and Diluted Earnings per Share	The following table sets forth the computation of basic and diluted earnings per common share: Year Ended December 31, 2015 2014 2013 Net income, basic and diluted $ 86,795 $ 84,401 $ 86,136 Weighted average common shares outstanding for basic earnings per share computation 45,184,091 44,615,060 43,566,681 Dilutive effects of stock-based compensation 462,327 595,501 477,921 Weighted average common shares outstanding for diluted earnings per common share computation 45,646,418 45,210,561 44,044,602 Basic earnings per common share $ 1.92 $ 1.89 $ 1.98 Diluted earnings per common share 1.90 1.87 1.96

Regulatory Capital (Tables)

Regulatory Capital (Tables)	12 Months Ended
	Dec. 31, 2015
Banking and Thrift [Abstract]
Schedule of Compliance with Regulatory Capital Requirements under Banking Regulations	The Company’s actual capital amounts and ratios and selected minimum regulatory thresholds and prompt corrective action provisions as of December 31, 2015 and 2014 are presented in the following tables: Actual Adequately Capitalized Basel III Phase-In Schedule Adequately Capitalized Basel III Fully Phased-In Well Capitalized (1) Amount Ratio Amount Ratio Amount Ratio Amount Ratio December 31, 2015 Total risk-based capital: Consolidated $ 946,156 15.4 % $ 492,692 8.0 % $ 646,658 10.50 % $ 615,865 10.0 % FIB 882,504 14.4 490,866 8.0 644,262 10.50 $ 613,582 10.0 Tier 1 risk-based capital: Consolidated 861,339 14.0 369,519 6.0 523,485 8.5 $ 492,692 8.0 FIB 805,805 13.1 368,149 6.0 521,545 8.5 $ 490,866 8.0 Common equity tier 1 risk-based capital: Consolidated 781,339 12.7 383,040 4.5 595,840 7.0 $ 400,312 6.5 FIB 805,805 13.1 381,730 4.5 593,802 7.0 $ 398,829 6.5 Leverage capital ratio: Consolidated 861,339 10.1 246,346 4.0 246,346 4.0 $ 425,600 5.0 FIB 805,805 9.5 245,433 4.0 245,433 4.0 $ 424,145 5.0 (1) The ratios for the well-capitalized requirement are only applicable to FIB. However, the Company manages its capital position as if the requirement applies to the consolidated entity and has presented the ratios as if they also applied on a consolidated basis. Actual Adequately Capitalized Well Capitalized (1) Amount Ratio Amount Ratio Amount Ratio December 31, 2014 Total risk-based capital: Consolidated $ 897,769 16.2 % $ 444,685 8.0 % $ 555,856 10.0 % FIB 832,907 15.1 442,468 8.0 553,085 10.0 Tier 1 risk-based capital: Consolidated 807,229 14.5 222,343 4.0 $ 333,514 6.0 FIB 754,708 13.7 221,234 4.0 331,851 6.0 Leverage capital ratio: Consolidated 807,229 9.6 335,897 4.0 $ 419,871 5.0 FIB 754,708 9.1 330,006 4.0 412,507 5.0 (1) The ratios for the well-capitalized requirement are only applicable to FIB. However, the Company manages its capital position as if the requirement applies to the consolidated entity and has presented the ratios as if they also applied on a consolidated basis. On July 2, 2013, the Board of Governors of the Federal Reserve Bank issued a final rule implementing a revised regulatory capital framework for U.S. banks in accordance with the Basel III international accord and satisfying related mandates under the Dodd-Frank Wall Street Reform and Consumer Protection Act. The revised regulatory capital framework (the "Basel III Capital Rules") substantially revised the risk-based capital requirements applicable to bank holding companies and depository institutions by defining the components of capital and addressing other issues affecting the numerator in banking institutions’ regulatory capital ratios, addressing risk weights and other issues affecting the denominator in banking institutions’ regulatory capital ratios and replacing the existing risk-weighting approach with a more risk-sensitive approach. The Basel III Capital Rules became effective for the Company on January 1, 2015, subject to a phase-in period for certain provisions.

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2015
Commitments and Contingencies Disclosure [Abstract]
Schedule of Future Minimum Rental Payments for Operating Leases	The total future minimum rental commitments, exclusive of maintenance and operating costs, required under operating leases that have initial or remaining noncancelable lease terms in excess of one year at December 31, 2015 , are as follows: Third Parties Related Entity Total For the year ending December 31: 2016 $ 1,913 $ 290 $ 2,203 2017 1,800 249 2,049 2018 1,537 138 1,675 2019 1,487 — 1,487 2020 1,349 — 1,349 Thereafter 8,655 — 8,655 Total $ 16,741 $ 677 $ 17,418

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Schedule of Income Tax Expense	Income tax expense consists of the following: Year ended December 31, 2015 2014 2013 Current: Federal $ 26,741 $ 34,941 $ 30,757 State 4,472 4,928 4,533 Total current 31,213 39,869 35,290 Deferred: Federal 11,047 4,870 10,056 State 1,402 475 1,220 Total deferred 12,449 5,345 11,276 Total income tax expense $ 43,662 $ 45,214 $ 46,566
Schedule of Effective Income Tax Rate Reconciliation	Total income tax expense differs from the amount computed by applying the statutory federal income tax rate of 35 percent in 2015 , 2014 and 2013 to income before income taxes as a result of the following: Year ended December 31, 2015 2014 2013 Tax expense at the statutory tax rate $ 45,660 $ 45,365 $ 46,446 Increase (decrease) in tax resulting from: Tax-exempt income (4,092 ) (4,255 ) (3,620 ) State income tax, net of federal income tax benefit 3,791 3,541 3,741 Federal tax credits (2,249 ) (313 ) (353 ) Other, net 552 876 352 Tax expense at effective tax rate $ 43,662 $ 45,214 $ 46,566
Schedule of Deferred Tax Assets and Liabilities	The tax effects of temporary differences between the financial statement carrying amounts and tax bases of assets and liabilities that give rise to significant portions of the net deferred tax asset (liability) relate to the following: December 31, 2015 2014 Deferred tax assets: Loans, principally due to allowance for loan losses $ 28,999 $ 28,506 Lease costs 596 719 Loss contingencies 108 1,785 Loan discount 4,552 7,022 Investment securities, unrealized losses 2,093 2,728 Employee benefits 9,009 8,256 Other real estate owned write-downs and carrying costs 598 2,536 Deferred gain on sale of subsidiary — 253 Deferred revenue on contract 1,087 481 Other 126 760 Deferred tax assets 47,168 53,046 Deferred tax liabilities: Fixed assets, principally differences in bases and depreciation (5,140 ) (569 ) Investment securities, unrealized gains (2,538 ) (1,351 ) Investment in joint venture partnership, principally due to differences in depreciation of partnership assets (1,301 ) (1,053 ) Prepaid amounts (1,139 ) (1,385 ) Government agency stock dividends (2,442 ) (2,407 ) Goodwill and core deposit intangibles (39,886 ) (36,732 ) Mortgage servicing rights (4,422 ) (4,144 ) Other (65 ) (531 ) Deferred tax liabilities (56,933 ) (48,172 ) Net deferred tax assets (liabilities) $ (9,765 ) $ 4,874

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	12 Months Ended
	Dec. 31, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Schedule of Share-based Compensation, Stock Options, Activity	The following table summarizes stock option activity under the Company’s active stock option plans for the year ended December 31, 2015 : Number of Shares Weighted-Average Exercise Price Weighted-Average Remaining Contract Life Outstanding options, beginning of year 1,748,032 $ 17.01 Exercised (350,438 ) 16.77 Forfeited (10,216 ) 16.82 Outstanding options, end of year 1,387,378 $ 17.06 3.68 years Outstanding options exercisable, end of year 1,265,596 $ 17.05 3.64 years Information with respect to the Company’s nonvested stock options as of and for the year ended December 31, 2015 follows: Number of Shares Weighted-Average Grant Date Fair Value Nonvested stock options, beginning of year 355,022 $ 3.62 Vested (225,961 ) 3.73 Forfeited (7,279 ) 3.48 Nonvested stock options, end of year 121,782 $ 3.48
Schedule of Share-based Compensation, Restricted Stock and Restricted Stock Units Activity	The following table presents information regarding the Company’s restricted stock as of December 31, 2015 : Number of Shares Weighted-Average Measurement Date Fair Value Restricted stock, beginning of year 248,399 $ 21.16 Granted 169,577 26.27 Vested (95,153 ) 18.65 Forfeited (16,583 ) 24.07 Canceled (2,601 ) 17.22 Restricted stock, end of year 303,639 $ 25.15

Other Comprehensive Income (Tab

Other Comprehensive Income (Tables)	12 Months Ended
	Dec. 31, 2015
Equity [Abstract]
Schedule of Comprehensive Income (Loss)	The gross amounts of each component of other comprehensive income and the related tax effects for the periods indicated are as follows: Year ended December 31, 2015 Before Tax Amount Tax Expense (Benefit) Net of Tax Amount Investment securities available-for sale: Change in net unrealized gain during period $ 5,863 $ 2,307 $ 3,556 Reclassification adjustment for net gains included in net income (137 ) (54 ) (83 ) Change in unamortized loss on available-for-sale securities transferred into held-to-maturity (1,101 ) (433 ) (668 ) Change in net unrealized gain on derivatives 165 65 100 Defined benefits post-retirement benefit plan: Change in net actuarial loss 58 23 35 Total other comprehensive income $ 4,848 $ 1,908 $ 2,940 Year ended December 31, 2014 Before Tax Amount Tax Expense (Benefit) Net of Tax Amount Investment securities available-for sale: Change in net unrealized gain during period $ 21,147 $ 8,321 $ 12,826 Reclassification adjustment for net gains included in net income (61 ) (24 ) (37 ) Unamortized premium on available-to-sale securities transferred into held-for-maturity (548 ) (216 ) (332 ) Defined benefits post-retirement benefit plan: Change in net actuarial loss 1,731 681 1,050 Total other comprehensive income $ 22,269 $ 8,762 $ 13,507 Year ended December 31, 2013 Before Tax Amount Tax Expense (Benefit) Net of Tax Amount Investment securities available-for sale: Change in net unrealized loss during period $ (52,949 ) $ (20,835 ) $ (32,114 ) Reclassification adjustment for net gains included in net income (1 ) — (1 ) Defined benefits post-retirement benefit plan: Change in net actuarial loss 137 54 83 Total other comprehensive loss $ (52,813 ) $ (20,781 ) $ (32,032 )
Schedule of Accumulated Other Comprehensive Income (Loss)	The components of accumulated other comprehensive income (loss), net of income taxes, are as follows: Year ended December 31, 2015 2014 Net unrealized gain (loss) on investment securities available-for-sale $ 684 $ (2,121 ) Net actuarial loss on defined benefit post-retirement benefit plans (378 ) (413 ) Net unrealized gain on derivatives 100 — Net accumulated other comprehensive income (loss) $ 406 $ (2,534 )

Condensed Financial Informati57

Condensed Financial Information (Parent Company Only) (Tables)	12 Months Ended
	Dec. 31, 2015
Condensed Financial Information of Parent Company Only Disclosure [Abstract]
Schedule of Condensed Financial Statements	Following is condensed financial information of First Interstate BancSystem, Inc. December 31, 2015 2014 Condensed balance sheets: Cash and cash equivalents $ 55,162 $ 65,483 Investment in subsidiaries, at equity: Bank subsidiary 975,236 936,817 Nonbank subsidiaries 1,985 1,982 Total investment in subsidiaries 977,221 938,799 Advances to subsidiaries, net 6,257 4,337 Other assets 39,668 29,335 Total assets $ 1,078,308 $ 1,037,954 Other liabilities $ 25,338 $ 26,553 Long-term debt 20,000 20,000 Subordinated debentures held by subsidiary trusts 82,477 82,477 Total liabilities 127,815 129,030 Stockholders’ equity 950,493 908,924 Total liabilities and stockholders’ equity $ 1,078,308 $ 1,037,954 Years Ended December 31, 2015 2014 2013 Condensed statements of income: Dividends from subsidiaries $ 70,000 $ 58,900 $ 71,400 Other interest income 23 42 34 Other income, primarily management fees from subsidiaries 13,207 12,166 12,809 Total income 83,230 71,108 84,243 Salaries and benefits 16,267 15,722 15,914 Interest expense 3,844 4,002 4,098 Acquisition expenses 795 4,017 — Other operating expenses, net 9,920 7,512 7,546 Total expenses 30,826 31,253 27,558 Earnings before income tax benefit 52,404 39,855 56,685 Income tax benefit (6,952 ) (6,862 ) (5,703 ) Income before undistributed earnings of subsidiaries 59,356 46,717 62,388 Undistributed earnings of subsidiaries 27,439 37,684 23,748 Net income $ 86,795 $ 84,401 $ 86,136 Years Ended December 31, 2015 2014 2013 Condensed statements of cash flows: Cash flows from operating activities: Net income $ 86,795 $ 84,401 $ 86,136 Adjustments to reconcile net income to cash provided by operating activities: Undistributed earnings of subsidiaries (27,439 ) (37,684 ) (23,748 ) Stock-based compensation expense 3,959 3,634 2,936 Tax benefits from stock-based compensation 1,443 2,193 1,898 Excess tax benefits from stock-based compensation (1,184 ) (2,205 ) (2,031 ) Other, net (11,333 ) 8,991 (5,804 ) Net cash provided by operating activities 52,241 59,330 59,387 Cash flows from investing activities: Acquisition of bank holding company, net of cash and cash equivalents received (7,207 ) (37,891 ) — Net cash used in investing activities $ (7,207 ) $ (37,891 ) $ — Years Ended December 31, 2015 2014 2013 Condensed statements of cash flows (continued): Cash flows from financing activities: Net (decrease) increase in advances from nonbank subsidiaries $ (2,021 ) $ (10,632 ) $ 6,992 Redemption of preferred stock — — (50,000 ) Repayment of long-term debt (950 ) — — Repayment of junior subordinated debentures held by subsidiary trusts — (20,439 ) — Proceeds from issuance of common stock, net of stock issuance costs 3,369 6,001 9,814 Excess tax benefits from stock-based compensation 1,184 2,205 2,031 Purchase and retirement of common stock (20,647 ) (9,739 ) (448 ) Dividends paid to common stockholders (36,290 ) (28,626 ) (17,909 ) Net cash used in financing activities (55,355 ) (61,230 ) (49,520 ) Net change in cash and cash equivalents (10,321 ) (39,791 ) 9,867 Cash and cash equivalents, beginning of year 65,483 105,274 95,407 Cash and cash equivalents, end of year $ 55,162 $ 65,483 $ 105,274

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2015
Fair Value Disclosures [Abstract]
Schedule of Financial Assets and Financial Liabilities Measured at Fair Value on a Recurring Basis	Financial assets and financial liabilities measured at fair value on a recurring basis are as follows: Fair Value Measurements at Reporting Date Using As of December 31, 2015 Balance Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Investment securities available-for-sale: U.S. Treasury Notes $ 3,911 $ — $ 3,911 $ — Obligations of U.S. government agencies 520,181 — 520,181 — U.S. agency mortgage-backed securities & collateralized mortgage obligations 929,046 — 929,046 — Private mortgage-backed securities 156 — 156 — Other investments 3,546 — 3,546 — Derivative assets: Interest rate swaps 953 — 953 — Derivative liabilities: Interest rate swaps 829 — 829 — Deferred compensation plan assets 10,149 — 10,149 — Deferred compensation plan liabilities 10,149 — 10,149 — Fair Value Measurements at Reporting Date Using As of December 31, 2014 Balance Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Investment securities available-for-sale: Obligations of U.S. government agencies $ 720,933 $ — $ 720,933 $ — U.S. agency mortgage-backed securities & collateralized mortgage obligations 990,666 — 990,666 — Private mortgage-backed securities 325 — 325 — Derivative assets: Interest rate swaps 61 — 61 — Derivative liabilities: Interest rate swaps 59 — 59 — Deferred compensation plan assets 10,312 — 10,312 — Deferred compensation plan liabilities 10,312 — 10,312 —
Schedule of Financial Assets and Financial Liabilities Measured at Fair Value on a Non-Recurring Basis	The following table presents information about the Company’s assets and liabilities measured at fair value on a non-recurring basis. Fair Value Measurements at Reporting Date Using As of December 31, 2015 Total Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Total Gains (Losses) Impaired loans $ 20,875 $ — $ — $ 20,875 $ (21,804 ) Other real estate owned 1,789 — — 1,789 (382 ) Long-lived assets to be disposed of by sale 1,506 — — 1,506 (857 ) Fair Value Measurements at Reporting Date Using As of December 31, 2014 Total Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Total Gains (Losses) Impaired loans $ 30,494 $ — $ — $ 30,494 $ (14,552 ) Other real estate owned 4,554 — — 4,554 (12,665 ) Long-lived assets to be disposed of by sale 1,083 — — 1,083 (702 )
Fair Value Inputs, Assets, Quantitative Information	As of December 31, 2015 Fair Value Valuation Technique Unobservable Inputs Range (Weighted Average) Impaired loans $ 20,875 Appraisal Appraisal adjustment 0% - 53% (38%) Other real estate owned 1,789 Appraisal Appraisal adjustment 2% - 96% (19%) Long-lived assets to be disposed of by sale 1,506 Appraisal Appraisal adjustment 0% - 9% (6%) As of December 31, 2014 Fair Value Valuation Technique Unobservable Inputs Range (Weighted Average) Impaired loans $ 30,494 Appraisal Appraisal adjustment 0% - 51% (19%) Other real estate owned 4,554 Appraisal Appraisal adjustment 0% - 50% (15%) Long-lived assets to be disposed of by sale 1,083 Appraisal Appraisal adjustment 0% - 9% (5%)
Fair Value, by Balance Sheet Grouping	A summary of the estimated fair values of financial instruments follows: ` Fair Value Measurements at Reporting Date Using As of December 31, 2015 Carrying Amount Estimated Fair Value Quoted Prices in Significant Other Significant Financial assets: Cash and cash equivalents $ 780,457 $ 780,457 $ 780,457 $ — $ — Investment securities available-for-sale 1,456,840 1,456,840 — 1,456,840 — Investment securities held-to-maturity 600,665 607,550 — 607,550 — Accrued interest receivable 27,729 27,729 — 27,729 — Mortgage servicing rights, net 15,621 31,011 — 31,011 — Net loans 5,169,379 5,128,705 — 5,107,830 20,875 Derivative assets 953 953 — 953 — Deferred compensation plan assets 10,149 10,149 — 10,149 — Total financial assets $ 8,061,793 $ 8,043,394 $ 780,457 $ 7,242,062 $ 20,875 Financial liabilities: Total deposits, excluding time deposits $ 5,957,345 $ 5,975,345 $ 5,975,345 $ — $ — Time deposits 1,131,592 1,137,289 — 1,137,289 — Securities sold under repurchase agreements 510,635 510,635 — 510,635 — Other borrowed funds 2 2 — 2 — Accrued interest payable 4,960 4,960 — 4,960 — Long-term debt 27,885 27,622 — 27,622 — Subordinated debentures held by subsidiary trusts 82,477 74,969 — 74,969 — Derivative liabilities 829 829 — 829 — Deferred compensation plan liabilities 10,149 10,149 — 10,149 — Total financial liabilities $ 7,725,874 $ 7,741,800 $ 5,975,345 $ 1,766,455 $ — Fair Value Measurements at Reporting Date Using As of December 31, 2014 Carrying Amount Estimated Fair Value Quoted Prices in Significant Other Significant Financial assets: Cash and cash equivalents $ 798,670 $ 798,670 $ 798,670 $ — $ — Investment securities available-for-sale 1,711,924 1,711,924 — 1,711,924 — Investment securities held-to-maturity 575,186 584,533 — 584,533 — Accrued interest receivable 27,063 27,063 — 27,063 — Mortgage servicing rights, net 14,038 21,434 — 21,434 — Net loans 4,823,243 4,800,725 — 4,770,231 30,494 Derivative assets 61 61 — 61 — Deferred compensation plan assets 10,312 10,312 — 10,312 — Total financial assets $ 7,960,497 $ 7,954,722 $ 798,670 $ 7,125,558 $ 30,494 Financial liabilities: Total deposits, excluding time deposits $ 5,767,992 $ 5,767,992 $ 5,767,992 $ — $ — Time deposits 1,238,220 1,244,324 — 1,244,324 — Securities sold under repurchase agreements 502,250 502,250 — 502,250 — Other borrowed funds 9 9 — 9 — Accrued interest payable 5,833 5,833 — 5,833 — Long-term debt 38,067 37,781 — 37,781 — Subordinated debentures held by subsidiary trusts 82,477 75,734 — 75,734 — Derivative liabilities 829 59 — 59 — Deferred compensation plan liabilities 10,149 10,312 — 10,312 — Total financial liabilities $ 7,645,826 $ 7,644,294 $ 5,767,992 $ 1,876,302 $ —

Summary of Significant Accoun59

Summary of Significant Accounting Policies (Details) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Other Real Estate, Foreclosed Assets, and Repossessed Assets [Abstract]
Other Real Estate, Foreclosed Assets, and Repossessed Assets	$ 1,686,000	$ 2,644
Cash and Cash Equivalents [Abstract]
Cash on deposit with Federal Reserve Bank	636,345,000	631,562,000
Compensating balances with Federal Reserve Bank	10,031,000	7,507,000
Loans and Leases Receivable Disclosure [Abstract]
Mortgage loans held for sale	52,875,000	40,828,000
Impairment losses	806,000	102,000	$ 616,000
Write-downs of OREO	207,000	224,000	3,512,000
Federal Home Loan Bank Stock and Federal Reserve Bank Stock [Abstract]
Federal Reserve Bank stock	16,421,000	16,187,000
Federal Home Loan Bank stock	10,135,000	10,662,000
Advertising expense	3,452,000	3,734,000	3,532,000
Share-based Compensation [Abstract]
Stock compensation expense	3,959,000	3,634,000	2,936,000
Tax benefits from stock-based compensation	$ 1,443,000	$ 1,390,000	$ 1,122,000

Summary of Significant Accoun60

Summary of Significant Accounting Policies - Premises and Equipment (Details)	12 Months Ended
	Dec. 31, 2015
Buildings and improvements | Minimum
Property, Plant and Equipment
Estimated useful lives	5 years
Buildings and improvements | Maximum
Property, Plant and Equipment
Estimated useful lives	45 years
Furniture and equipment | Minimum
Property, Plant and Equipment
Estimated useful lives	4 years
Furniture and equipment | Maximum
Property, Plant and Equipment
Estimated useful lives	15 years

Summary of Significant Accoun61

Summary of Significant Accounting Policies - Core Deposit Intangibles (Details) - Core Deposits Intangibles - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Intangible Assets, Net (Excluding Goodwill) [Abstract]
Accumulated core deposit intangibles amortization	$ 28,040	$ 24,652
Finite-Lived Intangible Assets, Net, Amortization Expense, Fiscal Year Maturity [Abstract]
2,015	3,220
2,016	1,933
2,017	1,414
2,018	1,201
2,019	988
Thereafter	$ 1,833

Acquisitions Business Combinati

Acquisitions Business Combinations (Details) $ / shares in Units, $ in Thousands	Jul. 24, 2015USD ($)	Jul. 31, 2014USD ($)$ / sharesshares	Dec. 31, 2015USD ($)shares	Dec. 31, 2014USD ($)	Dec. 31, 2013USD ($)	Oct. 17, 2104
Business Acquisition [Line Items]
Acquisition Expense			$ 795	$ 4,017	$ 0
Goodwill, Purchase Accounting Adjustments			$ 1,199
United Bank [Member]
Business Acquisition [Line Items]
Number of Subsidiary Banks	1
Number of Shared Markets	3
Estimate of Payments to Acquire Businesses, Gross	$ 7,234
Business Acquisition, Effective Date of Acquisition	Jul. 24, 2015
Mountain West Bank
Business Acquisition [Line Items]
Payments to Acquire Businesses, Gross		$ 38,479
Business Combination, Consideration Transferred		$ 74,451
Business Acquisition, Effective Date of Acquisition		Jul. 31, 2014
Business Acquisition, Date of Merger						Oct. 17, 2014
Mountain West Bank | Class A Common Stock
Business Acquisition [Line Items]
Business Acquisition, Equity Interest Issued or Issuable, Number of Shares | shares		1,378,230	1,378,230
Business Acquisition, Share Price | $ / shares		$ 26.10

Acquisitions Schedule of Recogn

Acquisitions Schedule of Recognized Identifiable Assets Acquired and Liabilities Assumed (Details) - USD ($) $ in Thousands	Jul. 24, 2015	Jul. 31, 2014	Dec. 31, 2015	Dec. 31, 2014
Business Acquisition [Line Items]
Business Acquisition, Equity Interest Issued or Issuable, Value Assigned			$ 35,972
Goodwill			$ 204,523	$ 205,574
Class A Common Stock
Business Acquisition [Line Items]
Business Acquisition, Equity Interest Issued or Issuable, Value Assigned		$ 35,972
United Bank Acquisition, as recorded by Company [Member]
Business Acquisition [Line Items]
Cash and Cash Equivalents	$ 5,598
Investment Securities	27,574
Loans	36,644
Allowance for Loan Losses	0
Premises and Equipment	3,128
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Company Owned LIfe Insurance	0
Core Deposit Intangibles	695
Other Assets	898
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets	74,537
Deposits	63,565
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Securities Under Agreement to Repurchase	2,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Long-term Debt	1,253
Other Liabilities	633
Subordinated Debentures Held by Subsidiary Trusts	0
Total Liabilities Assumed	67,451
Net Assets Acquired	7,086
Payments to Acquire Businesses, Gross	7,234
Business Acquisition, Equity Interest Issued or Issuable, Value Assigned	0
Business Combination, Consideration Transferred	7,234
Goodwill	$ 148
Mountain West Bank Acquisition, As Recorded by the Company
Business Acquisition [Line Items]
Cash and Cash Equivalents		74,035
Investment Securities		104,911
Loans		360,272
Allowance for Loan Losses		0
Premises and Equipment		29,436
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Company Owned LIfe Insurance		13,046
Core Deposit Intangibles		11,014
Other Assets		18,885
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets		611,599
Deposits		515,379
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Securities Under Agreement to Repurchase		0
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Long-term Debt		0
Other Liabilities		23,231
Subordinated Debentures Held by Subsidiary Trusts		20,439
Total Liabilities Assumed		559,049
Net Assets Acquired		52,550
Payments to Acquire Businesses, Gross		38,479
Business Acquisition, Equity Interest Issued or Issuable, Value Assigned		35,972
Business Combination, Consideration Transferred		74,451
Goodwill		$ 21,901

Acquisitions Finite Lived Intan

Acquisitions Finite Lived Intangible Assets Acquired as Part of a Business Combination (Details) - Core Deposits Intangibles - USD ($) $ in Thousands	Jul. 24, 2015	Jul. 31, 2014
Mountain West Bank
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-lived Intangible Assets Acquired		$ 11,014
Finite-Lived Intangible Asset, Useful Life		10 years
United Bank [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-lived Intangible Assets Acquired	$ 695
Finite-Lived Intangible Asset, Useful Life	10 years

Acquisitions Business Acquisiti

Acquisitions Business Acquisition, Pro Forma Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Business Acquisition [Line Items]
Pro Forma Interest Income		$ 280,102	$ 280,455
Pro Forma Non Interest Income		114,984	120,005
Business Acquisition, Pro Forma Revenue		395,086	400,460
Expenses Related to Acquisition Excluded From Pro Forma Net Income	$ 5,052
Business Acquisition, Pro Forma Net Income (Loss)		$ 87,129	$ 84,264

Investment Securities Amortized

Investment Securities Amortized Cost and Approximate Fair Values of Investment Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Available-for-Sale:
Available-for-Sale, Amortized Cost	$ 1,450,396	$ 1,708,494
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax	10,169	12,426
Available-for-sale Debt Securities, Accumulated Gross Unrealized Loss, before Tax	3,725	8,996
Available-for-Sale, Estimated Fair Value	1,456,840	1,711,924
Held-to-Maturity:
Held-to-Maturity, Amortized Cost	600,665	575,186
Held-to-maturity Securities, Accumulated Unrecognized Holding Gain	12,854	11,566
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	(5,969)	(2,219)
Held-to-Maturity Estimated Fair Value	607,550	584,533
US Treasury Securities [Member]
Available-for-Sale:
Available-for-Sale, Amortized Cost	3,912
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax	3
Available-for-sale Debt Securities, Accumulated Gross Unrealized Loss, before Tax	4
Available-for-Sale, Estimated Fair Value	3,911
Obligations of U.S. government agencies
Available-for-Sale:
Available-for-Sale, Amortized Cost	521,079	725,408
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax	712	895
Available-for-sale Debt Securities, Accumulated Gross Unrealized Loss, before Tax	1,610	5,370
Available-for-Sale, Estimated Fair Value	520,181	720,933
U.S. agency residential mortgage-backed securities & collateralized mortgage obligations
Available-for-Sale:
Available-for-Sale, Amortized Cost	921,699	982,764
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax	9,448	11,526
Available-for-sale Debt Securities, Accumulated Gross Unrealized Loss, before Tax	2,101	3,624
Available-for-Sale, Estimated Fair Value	929,046	990,666
Held-to-Maturity:
Held-to-Maturity, Amortized Cost	376,480	353,176
Held-to-maturity Securities, Accumulated Unrecognized Holding Gain	7,686	5,563
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	(5,522)	(1,758)
Held-to-Maturity Estimated Fair Value	378,644	356,981
Other Investments
Held-to-Maturity:
Held-to-Maturity, Amortized Cost	354	504
Held-to-maturity Securities, Accumulated Unrecognized Holding Gain	1	0
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	0	0
Held-to-Maturity Estimated Fair Value	355	504
State, county and municipal securities
Held-to-Maturity:
Held-to-Maturity, Amortized Cost	173,785	188,941
Held-to-maturity Securities, Accumulated Unrecognized Holding Gain	5,103	5,949
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	(227)	(386)
Held-to-Maturity Estimated Fair Value	178,661	194,504
Corporate securities
Held-to-Maturity:
Held-to-Maturity, Amortized Cost	50,046	32,565
Held-to-maturity Securities, Accumulated Unrecognized Holding Gain	64	54
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	(220)	(75)
Held-to-Maturity Estimated Fair Value	49,890	32,544
Private mortgage-backed securities
Available-for-Sale:
Available-for-Sale, Amortized Cost	156	322
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax	1	5
Available-for-sale Debt Securities, Accumulated Gross Unrealized Loss, before Tax	1	2
Available-for-Sale, Estimated Fair Value	156	$ 325
Other Investments
Available-for-Sale:
Available-for-Sale, Amortized Cost	3,550
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax	5
Available-for-sale Debt Securities, Accumulated Gross Unrealized Loss, before Tax	9
Available-for-Sale, Estimated Fair Value	$ 3,546

Investment Securities Realized

Investment Securities Realized Gains (Losses) on Investments (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Investments, Debt and Equity Securities [Abstract]
Gross realized gains	$ 156	$ 274	$ 49
Gross realized losses	19	$ 213	$ 48
State, county and municipal securities
Schedule of Available-for-sale Securities
Available-for-sale Securities, Amortized Cost Basis	140,458
State, county and municipal securities | Montana, Wyoming, and South Dakota
Schedule of Available-for-sale Securities
Available-for-sale Securities, Amortized Cost Basis	$ 78,337

Investment Securities Transfer

Investment Securities Transfer from AFS to HTM (Details) - USD ($) $ in Thousands	Oct. 30, 2015	Jun. 27, 2014
Schedule of Available for Sale and Held-to-Maturity Securities
Remaining Expected Lives of Available-for-Sale Securities Transferred to Held-to-Maturity	4 years	4 years 3 months 17 days
U.S. agency residential mortgage-backed securities & collateralized mortgage obligations
Schedule of Available for Sale and Held-to-Maturity Securities
Available-for-Sale Securities Transferred to Held-to-Maturity, Amortized Costs	$ 100,343	$ 396,640
Available-for-Sale Securities Transferred to Held-to-Maturity, Fair Values	100,140	388,808
Available-for-Sale Securities Transferred to Held-to-Maturity, Unrealized Net Gain (Loss)	$ 203	$ 7,832

Investment Securities Gross Unr

Investment Securities Gross Unrealized Losses and Fair Values of Investment Securities (Details) $ in Thousands	Dec. 31, 2015USD ($)securities	Dec. 31, 2014USD ($)securities
Available-for-Sale:
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	$ 556,823	$ 355,102
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(2,667)	(1,589)
Available-for-Sale, 12 months or more fair value	82,690	460,753
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(1,058)	(7,407)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	639,513	815,855
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	(3,725)	(8,996)
Held-to-Maturity:
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	128,350	83,935
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(4,649)	(1,846)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	79,015	20,097
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(1,320)	(373)
Held-to-maturity Securities, Fair Value	207,365	104,032
Held-to-maturity Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ (5,969)	$ (2,219)
Available-for-Sale and Held-to-Maturity:
Investment securities in an unrealized loss position (number of securities) | securities	198	154
US Treasury Securities [Member]
Available-for-Sale:
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	$ 2,092
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(4)
Available-for-Sale, 12 months or more fair value	0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	2,092
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	(4)
State, county and municipal securities
Held-to-Maturity:
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	10,182	$ 7,979
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(39)	(13)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	9,476	20,097
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(188)	(373)
Held-to-maturity Securities, Fair Value	19,658	28,076
Held-to-maturity Securities, Continuous Unrealized Loss Position, Accumulated Loss	(227)	(386)
Obligations of U.S. government agencies
Available-for-Sale:
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	209,631	135,888
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(1,077)	(702)
Available-for-Sale, 12 months or more fair value	54,619	309,283
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(533)	(4,668)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	264,250	445,171
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	(1,610)	(5,370)
U.S. agency residential mortgage-backed securities & collateralized mortgage obligations
Available-for-Sale:
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	343,875	219,214
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(1,577)	(887)
Available-for-Sale, 12 months or more fair value	28,010	151,380
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(524)	(2,737)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	371,885	370,594
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	(2,101)	(3,624)
Held-to-Maturity:
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	87,033	61,201
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(4,390)	(1,758)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	69,539	0
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(1,132)	0
Held-to-maturity Securities, Fair Value	156,572	61,201
Held-to-maturity Securities, Continuous Unrealized Loss Position, Accumulated Loss	(5,522)	(1,758)
Private mortgage-backed securities
Available-for-Sale:
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	0	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0	0
Available-for-Sale, 12 months or more fair value	61	90
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(1)	(2)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	61	90
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	(1)	(2)
Corporate securities
Held-to-Maturity:
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	31,135	14,755
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(220)	(75)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	0	0
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	0
Held-to-maturity Securities, Fair Value	31,135	14,755
Held-to-maturity Securities, Continuous Unrealized Loss Position, Accumulated Loss	(220)	$ (75)
Other Investments
Available-for-Sale:
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	1,225
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(9)
Available-for-Sale, 12 months or more fair value	0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	1,225
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ (9)

Investment Securities Maturitie

Investment Securities Maturities of Investment Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Rolling Maturity
Available-for-sale amortized cost, within one year	$ 329,638
Available-for-sale amortized cost, after one year but within five years	1,018,573
Available-for-sale amortized cost, after five years but within ten years	46,874
Available-for-sale amortized cost, after ten years	55,311
Available-for-Sale, Amortized Cost	1,450,396	$ 1,708,494
Available-for-sale Securities, Debt Maturities, Fair Value, Rolling Maturity
Available-for-sale estimated fair value, within one year	331,620
Available-for-sale estimated fair value, after one year but within five years	1,022,351
Available-for-sale estimated fair value, after ten years	47,117
Available-for-ale estimated fair value, after five years but within ten years	55,752
Available-for-Sale, Estimated Fair Value	1,456,840	1,711,924
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount
Held-to-maturity amortized cost, within one year	100,695
Held-to-maturity amoritzed cost, after one year but within five years	320,310
Held-to-maturity amortized cost, after five years but within ten years	134,606
Held-to-maturity amortized cost, after ten years	45,054
Held-to-Maturity, Amortized Cost	600,665	575,186
Held-to-maturity Securities, Debt Maturities, Fair Value, Rolling Maturity
Held-to-maturity estimated fair value, within one year	101,885
Held-to-maturity estimated fair value, after one year but within five years	322,281
Held-to-maturity estimated fair value, after five years but within ten years	137,304
Held-to-maturity estimated fair value, after ten years	46,080
Held-to-Maturity Estimated Fair Value	607,550	584,533
Available-for-sale Securities and Held-to-maturity Securities
Securities sold under agreements to repurchase	1,325,078	1,351,787
Pledged assets separately reported, securities pledged for repurchase agreements, at fair value	1,328,571	1,356,341
Callable within one year
Available-for-sale Securities and Held-to-maturity Securities
Investment securities primarily classified as available-for-sale, amortized costs, after one year but within five years	98,885
Investment securities primarily classified as available-for-sale, fair value, after one year but within five years	98,664
Mortgage Backed Securities, Variable Rate
Available-for-sale Securities and Held-to-maturity Securities
Available-for-sale securities, amortized cost basis	$ 68,440	$ 40,666

Loans - Schedule of Loans by C

Loans - Schedule of Loans by Class (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Loans and Leases Receivable
Loans held for investment	$ 5,193,321	$ 4,856,615
Mortgage loans held for sale	52,875	40,828
Total loans	5,246,196	4,897,443
Land acquisition & development construction real estate
Loans and Leases Receivable
Loans held for investment	224,066	220,443
Residential construction real estate
Loans and Leases Receivable
Loans held for investment	111,763	96,580
Commercial Construction
Loans and Leases Receivable
Loans held for investment	94,890	101,246
Total construction loans
Loans and Leases Receivable
Loans held for investment	430,719	418,269
Residential real estate
Loans and Leases Receivable
Loans held for investment	$ 1,032,851	999,903
Loans receivable, maturity	15 years
Agricultural real estate
Loans and Leases Receivable
Loans held for investment	$ 156,234	167,659
Total real estate loans
Loans and Leases Receivable
Loans held for investment	3,413,062	3,225,253
Indirect consumer
Loans and Leases Receivable
Loans held for investment	622,529	552,863
Other consumer
Loans and Leases Receivable
Loans held for investment	153,717	144,141
Credit card consumer
Loans and Leases Receivable
Loans held for investment	68,107	65,467
Total consumer loans
Loans and Leases Receivable
Loans held for investment	844,353	762,471
Commercial
Loans and Leases Receivable
Loans held for investment	792,416	740,073
Agricultural
Loans and Leases Receivable
Loans held for investment	142,151	124,859
Other, including overdrafts
Loans and Leases Receivable
Loans held for investment	1,339	3,959
Commercial real estate
Loans and Leases Receivable
Loans held for investment	$ 1,793,258	1,639,422
Loans receivable, maturity	5 years
Loans held for investment
Loans and Leases Receivable
Loans held for investment	$ 5,193,321	4,856,615
Total loans
Loans and Leases Receivable
Total loans	5,246,196	4,897,443
Home equity line of credit
Loans and Leases Receivable
Loans held for investment	$ 298,661	$ 298,692
Loans receivable, loan to value limit	80.00%

Loans Schedule of Loans Acquire

Loans Schedule of Loans Acquired from Business Combinations (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Deteriorated Loans Transferred in [Abstract]
Outstanding Balance	$ 33,755	$ 41,910
Loans on Accrual Status	21,507	31,870
Loans on Non-Accrual Status	0	0
Total Carrying Value	$ 21,507	$ 31,870

Loans Certain Loans Acquired in

Loans Certain Loans Acquired in Transfer Not Accounted for as Debt Securities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Accretable Yield Rollforward [Abstract]
Beginning Balance	$ 5,781	$ 0
Acquisitions	432	5,233
Accretion Income	(2,884)	(735)
Acquisition	594	0
Reductions Due to Exit Events	(517)	(201)
Reclassifications from (to) nonaccretable differences	3,307	1,484
Ending Balance	$ 6,713	$ 5,781

Loans - Schedule of Recorded I

Loans - Schedule of Recorded Investment in Past Due Loans by Class (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Loans and Leases Receivable Recorded Investment, Past Due
Loans held for investment	$ 5,193,321	$ 4,856,615
Mortgage loans held for sale	52,875	40,828
Total loans	5,246,196	4,897,443
Interest Income on Non-Accrual Loans if Accrued	3,150	3,970	$ 4,630
Commercial real estate
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due	7,193	6,632
Current Loans	1,762,294	1,605,421
Non-accrual Loans	23,771	27,369
Loans held for investment	1,793,258	1,639,422
Land acquisition & development construction real estate
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due	4,678	1,222
Current Loans	212,757	210,969
Non-accrual Loans	6,631	8,252
Loans held for investment	224,066	220,443
Residential construction real estate
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due	1,288	475
Current Loans	110,182	95,833
Non-accrual Loans	293	272
Loans held for investment	111,763	96,580
Commercial Construction
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due	3,232	100
Current Loans	90,703	98,582
Non-accrual Loans	955	2,564
Loans held for investment	94,890	101,246
Total construction loans
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due	9,198	1,797
Current Loans	413,642	405,384
Non-accrual Loans	7,879	11,088
Loans held for investment	430,719	418,269
Residential real estate
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due	9,250	9,376
Current Loans	1,018,359	987,735
Non-accrual Loans	5,242	2,792
Loans held for investment	1,032,851	999,903
Agricultural real estate
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due	193	1,860
Current Loans	150,686	158,957
Non-accrual Loans	5,355	6,842
Loans held for investment	156,234	167,659
Total real estate loans
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due	25,834	19,665
Current Loans	3,344,981	3,157,497
Non-accrual Loans	42,247	48,091
Loans held for investment	3,413,062	3,225,253
Indirect consumer
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due	7,974	3,723
Current Loans	614,029	548,757
Non-accrual Loans	526	383
Loans held for investment	622,529	552,863
Other consumer
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due	1,677	1,160
Current Loans	151,381	142,432
Non-accrual Loans	659	549
Loans held for investment	153,717	144,141
Credit card consumer
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due	1,327	968
Current Loans	66,768	64,484
Non-accrual Loans	12	15
Loans held for investment	68,107	65,467
Total consumer loans
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due	10,978	5,851
Current Loans	832,178	755,673
Non-accrual Loans	1,197	947
Loans held for investment	844,353	762,471
Commercial
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due	10,252	4,800
Current Loans	759,851	722,575
Non-accrual Loans	22,313	12,698
Loans held for investment	792,416	740,073
Agricultural
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due	1,093	1,125
Current Loans	140,430	123,288
Non-accrual Loans	628	446
Loans held for investment	142,151	124,859
Other, including overdrafts
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due	314	0
Current Loans	1,025	3,959
Non-accrual Loans	0	0
Loans held for investment	1,339	3,959
Loans held for investment
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due	48,471	31,441
Current Loans	5,078,465	4,762,992
Non-accrual Loans	66,385	62,182
Loans held for investment	5,193,321	4,856,615
Mortgage loans originated for sale
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due	0	0
Current Loans	52,875	40,828
Non-accrual Loans	0	0
Total loans
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due	48,471	31,441
Current Loans	5,131,340	4,803,820
Non-accrual Loans	66,385	62,182
Total loans	5,246,196	4,897,443
Financing Receivables, 30 to 59 Days Past Due [Member] | Commercial real estate
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due	6,051	4,692
Financing Receivables, 30 to 59 Days Past Due [Member] | Land acquisition & development construction real estate
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due	3,190	839
Financing Receivables, 30 to 59 Days Past Due [Member] | Residential construction real estate
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due	1,288	0
Financing Receivables, 30 to 59 Days Past Due [Member] | Commercial Construction
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due	3,232	100
Financing Receivables, 30 to 59 Days Past Due [Member] | Total construction loans
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due	7,710	939
Financing Receivables, 30 to 59 Days Past Due [Member] | Residential real estate
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due	5,991	6,969
Financing Receivables, 30 to 59 Days Past Due [Member] | Agricultural real estate
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due	176	1,624
Financing Receivables, 30 to 59 Days Past Due [Member] | Total real estate loans
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due	19,928	14,224
Financing Receivables, 30 to 59 Days Past Due [Member] | Indirect consumer
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due	6,675	3,235
Financing Receivables, 30 to 59 Days Past Due [Member] | Other consumer
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due	1,312	988
Financing Receivables, 30 to 59 Days Past Due [Member] | Credit card consumer
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due	533	369
Financing Receivables, 30 to 59 Days Past Due [Member] | Total consumer loans
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due	8,520	4,592
Financing Receivables, 30 to 59 Days Past Due [Member] | Commercial
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due	8,493	3,659
Financing Receivables, 30 to 59 Days Past Due [Member] | Agricultural
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due	879	1,125
Financing Receivables, 30 to 59 Days Past Due [Member] | Other, including overdrafts
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due	0	0
Financing Receivables, 30 to 59 Days Past Due [Member] | Loans held for investment
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due	37,820	23,600
Financing Receivables, 30 to 59 Days Past Due [Member] | Mortgage loans originated for sale
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due	0	0
Financing Receivables, 30 to 59 Days Past Due [Member] | Total loans
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due	37,820	23,600
Financing Receivables, 60 to 89 Days Past Due [Member] | Commercial real estate
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due	724	1,609
Financing Receivables, 60 to 89 Days Past Due [Member] | Land acquisition & development construction real estate
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due	163	383
Financing Receivables, 60 to 89 Days Past Due [Member] | Residential construction real estate
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due	0	475
Financing Receivables, 60 to 89 Days Past Due [Member] | Commercial Construction
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due	0	0
Financing Receivables, 60 to 89 Days Past Due [Member] | Total construction loans
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due	163	858
Financing Receivables, 60 to 89 Days Past Due [Member] | Residential real estate
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due	1,196	645
Financing Receivables, 60 to 89 Days Past Due [Member] | Agricultural real estate
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due	17	236
Financing Receivables, 60 to 89 Days Past Due [Member] | Total real estate loans
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due	2,100	3,348
Financing Receivables, 60 to 89 Days Past Due [Member] | Indirect consumer
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due	1,089	482
Financing Receivables, 60 to 89 Days Past Due [Member] | Other consumer
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due	331	140
Financing Receivables, 60 to 89 Days Past Due [Member] | Credit card consumer
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due	317	284
Financing Receivables, 60 to 89 Days Past Due [Member] | Total consumer loans
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due	1,737	906
Financing Receivables, 60 to 89 Days Past Due [Member] | Commercial
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due	1,060	994
Financing Receivables, 60 to 89 Days Past Due [Member] | Agricultural
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due	152	0
Financing Receivables, 60 to 89 Days Past Due [Member] | Other, including overdrafts
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due	0	0
Financing Receivables, 60 to 89 Days Past Due [Member] | Loans held for investment
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due	5,049	5,248
Financing Receivables, 60 to 89 Days Past Due [Member] | Mortgage loans originated for sale
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due	0	0
Financing Receivables, 60 to 89 Days Past Due [Member] | Total loans
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due	5,049	5,248
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Commercial real estate
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due	418	331
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Land acquisition & development construction real estate
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due	1,325	0
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Residential construction real estate
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due	0	0
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Commercial Construction
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due	0	0
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Total construction loans
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due	1,325	0
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Residential real estate
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due	2,063	1,762
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Agricultural real estate
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due	0	0
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Total real estate loans
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due	3,806	2,093
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Indirect consumer
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due	210	6
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Other consumer
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due	34	32
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Credit card consumer
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due	477	315
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Total consumer loans
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due	721	353
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Commercial
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due	699	147
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Agricultural
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due	62	0
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Other, including overdrafts
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due	314	0
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Loans held for investment
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due	5,602	2,593
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Mortgage loans originated for sale
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due	0	0
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Total loans
Loans and Leases Receivable Recorded Investment, Past Due
Total Loans 30 or More Days Past Due	$ 5,602	$ 2,593

Loans - Schedule of Recorded75

Loans - Schedule of Recorded Investment in Impaired Loans (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Impaired Financing Receivable, Unpaid Principal Balance
Unpaid Total Principal Balance	$ 120,387	$ 87,240	$ 124,867
Recorded Investment With No Allowance	56,236	57,050	62,724
Recorded Investment With Allowance	35,729	21,430	47,848
Total Recorded Investment	91,965	78,480	110,572
Related Allowance	11,575	5,792	8,929
Impaired Financing Receivable, Average Recorded Investment	80,310	97,655	123,376
Impaired Financing Receivable, Interest Income, Cash Basis Method	1,034	1,083	1,692
Impaired Loans, interest lost on nonaccrual loans	3,935	4,951	5,786
Commercial real estate
Impaired Financing Receivable, Unpaid Principal Balance
Unpaid Total Principal Balance	58,179	41,603	64,780
Recorded Investment With No Allowance	27,882	28,143	29,216
Recorded Investment With Allowance	17,614	11,246	33,937
Total Recorded Investment	45,496	39,389	63,153
Related Allowance	3,401	1,608	5,210
Impaired Financing Receivable, Average Recorded Investment	39,233	54,701	66,330
Impaired Financing Receivable, Interest Income, Cash Basis Method	784	876	1,092
Land acquisition & development construction real estate
Impaired Financing Receivable, Unpaid Principal Balance
Unpaid Total Principal Balance	15,503	12,511	23,906
Recorded Investment With No Allowance	7,245	7,262	9,901
Recorded Investment With Allowance	778	1,615	7,226
Total Recorded Investment	8,023	8,877	17,127
Related Allowance	282	574	1,434
Impaired Financing Receivable, Average Recorded Investment	8,337	13,056	19,523
Impaired Financing Receivable, Interest Income, Cash Basis Method	54	43	487
Residential construction real estate
Impaired Financing Receivable, Unpaid Principal Balance
Unpaid Total Principal Balance	992	459	1,816
Recorded Investment With No Allowance	293	272	1,095
Recorded Investment With Allowance	0	0	277
Total Recorded Investment	293	272	1,372
Related Allowance	0	0	26
Impaired Financing Receivable, Average Recorded Investment	282	822	1,893
Impaired Financing Receivable, Interest Income, Cash Basis Method	0	0	0
Commercial Construction
Impaired Financing Receivable, Unpaid Principal Balance
Unpaid Total Principal Balance	1,264	2,729	397
Recorded Investment With No Allowance	340	253	279
Recorded Investment With Allowance	739	2,442	84
Total Recorded Investment	1,079	2,695	363
Related Allowance	739	904	85
Impaired Financing Receivable, Average Recorded Investment	1,887	1,529	3,936
Impaired Financing Receivable, Interest Income, Cash Basis Method	7	8	4
Total construction loans
Impaired Financing Receivable, Unpaid Principal Balance
Unpaid Total Principal Balance	17,759	15,699	26,119
Recorded Investment With No Allowance	7,878	7,787	11,275
Recorded Investment With Allowance	1,517	4,057	7,587
Total Recorded Investment	9,395	11,844	18,862
Related Allowance	1,021	1,478	1,545
Impaired Financing Receivable, Average Recorded Investment	10,506	15,407	25,352
Impaired Financing Receivable, Interest Income, Cash Basis Method	61	51	491
Residential real estate
Impaired Financing Receivable, Unpaid Principal Balance
Unpaid Total Principal Balance	7,073	2,959	9,448
Recorded Investment With No Allowance	3,547	2,452	5,081
Recorded Investment With Allowance	2,317	341	967
Total Recorded Investment	5,864	2,793	6,048
Related Allowance	367	143	249
Impaired Financing Receivable, Average Recorded Investment	4,055	4,537	8,104
Impaired Financing Receivable, Interest Income, Cash Basis Method	1	5	17
Agricultural real estate
Impaired Financing Receivable, Unpaid Principal Balance
Unpaid Total Principal Balance	6,434	8,844	8,895
Recorded Investment With No Allowance	5,563	6,444	6,429
Recorded Investment With Allowance	198	2,305	2,370
Total Recorded Investment	5,761	8,749	8,799
Related Allowance	5	732	335
Impaired Financing Receivable, Average Recorded Investment	7,156	8,774	8,230
Impaired Financing Receivable, Interest Income, Cash Basis Method	39	78	8
Total real estate loans
Impaired Financing Receivable, Unpaid Principal Balance
Unpaid Total Principal Balance	89,445	69,105	109,242
Recorded Investment With No Allowance	44,870	44,826	52,001
Recorded Investment With Allowance	21,646	17,949	44,861
Total Recorded Investment	66,516	62,775	96,862
Related Allowance	4,794	3,961	7,339
Impaired Financing Receivable, Average Recorded Investment	60,950	83,419	108,016
Impaired Financing Receivable, Interest Income, Cash Basis Method	885	1,010	1,608
Commercial
Impaired Financing Receivable, Unpaid Principal Balance
Unpaid Total Principal Balance	29,593	16,904	15,448
Recorded Investment With No Allowance	10,744	11,882	10,684
Recorded Investment With Allowance	13,727	2,644	2,901
Total Recorded Investment	24,471	14,526	13,585
Related Allowance	6,487	1,190	1,504
Impaired Financing Receivable, Average Recorded Investment	18,502	13,789	15,047
Impaired Financing Receivable, Interest Income, Cash Basis Method	123	50	68
Agricultural
Impaired Financing Receivable, Unpaid Principal Balance
Unpaid Total Principal Balance	1,349	1,231	177
Recorded Investment With No Allowance	622	342	39
Recorded Investment With Allowance	356	837	86
Total Recorded Investment	978	1,179	125
Related Allowance	294	641	86
Impaired Financing Receivable, Average Recorded Investment	858	447	313
Impaired Financing Receivable, Interest Income, Cash Basis Method	$ 26	$ 23	$ 16

Loans - Schedule of Loans Rene

Loans - Schedule of Loans Renegotiated in Troubled Debt Restructurings (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2015USD ($)notes	Dec. 31, 2014USD ($)notes	Dec. 31, 2013USD ($)notes
Loans and Leases Receivable, Troubled Debt Restructuring
Financing Receivable, Modifications, Subsequent Default, Number of Contracts	3
Financing Receivable, Modifications, Subsequent Default, Recorded Investment	$ 244
Financing Receivables, Impaired, Troubled Debt Restructuring, Write-down	0	$ 0	$ 0
Loans renegotiated in troubled debt restructurings	40,330	44,227
Loans renegotiated in troubled debt restructurings, non-accrual loans	24,911	23,275
Loans tenegotiated in troubled debt restructurings, accrual loans	$ 15,419	$ 20,952
Financing receivable, modifications, subsequent default, number of contracts, during period | notes	15	20	43
Financing Receivable, Modifications, Pre-Modification Recorded Investment	$ 13,148	$ 7,190	$ 28,403
Commercial real estate
Loans and Leases Receivable, Troubled Debt Restructuring
Financing receivable, modifications, subsequent default, number of contracts, during period | notes	2	13	19
Financing Receivable, Modifications, Pre-Modification Recorded Investment	$ 682	$ 6,556	$ 15,651
Land acquisition & development construction real estate
Loans and Leases Receivable, Troubled Debt Restructuring
Financing receivable, modifications, subsequent default, number of contracts, during period | notes			8
Financing Receivable, Modifications, Pre-Modification Recorded Investment			$ 9,788
Residential construction real estate
Loans and Leases Receivable, Troubled Debt Restructuring
Financing receivable, modifications, subsequent default, number of contracts, during period | notes			3
Financing Receivable, Modifications, Pre-Modification Recorded Investment			$ 819
Total construction loans
Loans and Leases Receivable, Troubled Debt Restructuring
Financing receivable, modifications, subsequent default, number of contracts, during period | notes			11
Financing Receivable, Modifications, Pre-Modification Recorded Investment			$ 10,607
Residential real estate
Loans and Leases Receivable, Troubled Debt Restructuring
Financing receivable, modifications, subsequent default, number of contracts, during period | notes		1	5
Financing Receivable, Modifications, Pre-Modification Recorded Investment		$ 15	$ 787
Agricultural real estate
Loans and Leases Receivable, Troubled Debt Restructuring
Financing receivable, modifications, subsequent default, number of contracts, during period | notes			1
Financing Receivable, Modifications, Pre-Modification Recorded Investment			$ 188
Total real estate loans
Loans and Leases Receivable, Troubled Debt Restructuring
Financing receivable, modifications, subsequent default, number of contracts, during period | notes		14	36
Financing Receivable, Modifications, Pre-Modification Recorded Investment		$ 6,571	$ 27,233
Total consumer loans
Loans and Leases Receivable, Troubled Debt Restructuring
Financing receivable, modifications, subsequent default, number of contracts, during period | notes		1	1
Financing Receivable, Modifications, Pre-Modification Recorded Investment		$ 113	$ 27
Indirect consumer
Loans and Leases Receivable, Troubled Debt Restructuring
Financing Receivable, Modifications, Subsequent Default, Number of Contracts	1
Financing Receivable, Modifications, Subsequent Default, Recorded Investment	$ 4
Financing receivable, modifications, subsequent default, number of contracts, during period | notes	1
Financing Receivable, Modifications, Pre-Modification Recorded Investment	$ 4
Commercial
Loans and Leases Receivable, Troubled Debt Restructuring
Financing Receivable, Modifications, Subsequent Default, Number of Contracts	2
Financing Receivable, Modifications, Subsequent Default, Recorded Investment	$ 240
Financing receivable, modifications, subsequent default, number of contracts, during period | notes	12	5	6
Financing Receivable, Modifications, Pre-Modification Recorded Investment	$ 12,462	$ 506	$ 1,143
Interest Only Period Concession [Member]
Loans and Leases Receivable, Troubled Debt Restructuring
Financing Receivable, Modifications, Pre-Modification Recorded Investment	0	5,229	1,684
Interest Only Period Concession [Member] | Commercial real estate
Loans and Leases Receivable, Troubled Debt Restructuring
Financing Receivable, Modifications, Pre-Modification Recorded Investment	0	4,753	543
Interest Only Period Concession [Member] | Land acquisition & development construction real estate
Loans and Leases Receivable, Troubled Debt Restructuring
Financing Receivable, Modifications, Pre-Modification Recorded Investment			528
Interest Only Period Concession [Member] | Residential construction real estate
Loans and Leases Receivable, Troubled Debt Restructuring
Financing Receivable, Modifications, Pre-Modification Recorded Investment			0
Interest Only Period Concession [Member] | Total construction loans
Loans and Leases Receivable, Troubled Debt Restructuring
Financing Receivable, Modifications, Pre-Modification Recorded Investment			528
Interest Only Period Concession [Member] | Residential real estate
Loans and Leases Receivable, Troubled Debt Restructuring
Financing Receivable, Modifications, Pre-Modification Recorded Investment		0	0
Interest Only Period Concession [Member] | Agricultural real estate
Loans and Leases Receivable, Troubled Debt Restructuring
Financing Receivable, Modifications, Pre-Modification Recorded Investment			0
Interest Only Period Concession [Member] | Total real estate loans
Loans and Leases Receivable, Troubled Debt Restructuring
Financing Receivable, Modifications, Pre-Modification Recorded Investment		4,753	1,071
Interest Only Period Concession [Member] | Total consumer loans
Loans and Leases Receivable, Troubled Debt Restructuring
Financing Receivable, Modifications, Pre-Modification Recorded Investment		0	0
Interest Only Period Concession [Member] | Indirect consumer
Loans and Leases Receivable, Troubled Debt Restructuring
Financing Receivable, Modifications, Pre-Modification Recorded Investment	0
Interest Only Period Concession [Member] | Commercial
Loans and Leases Receivable, Troubled Debt Restructuring
Financing Receivable, Modifications, Pre-Modification Recorded Investment	0	476	613
Interest rate adjustment
Loans and Leases Receivable, Troubled Debt Restructuring
Financing Receivable, Modifications, Pre-Modification Recorded Investment	3,318	84	14,263
Interest rate adjustment | Commercial real estate
Loans and Leases Receivable, Troubled Debt Restructuring
Financing Receivable, Modifications, Pre-Modification Recorded Investment	0	84	11,420
Interest rate adjustment | Land acquisition & development construction real estate
Loans and Leases Receivable, Troubled Debt Restructuring
Financing Receivable, Modifications, Pre-Modification Recorded Investment			1,952
Interest rate adjustment | Residential construction real estate
Loans and Leases Receivable, Troubled Debt Restructuring
Financing Receivable, Modifications, Pre-Modification Recorded Investment			411
Interest rate adjustment | Total construction loans
Loans and Leases Receivable, Troubled Debt Restructuring
Financing Receivable, Modifications, Pre-Modification Recorded Investment			2,363
Interest rate adjustment | Residential real estate
Loans and Leases Receivable, Troubled Debt Restructuring
Financing Receivable, Modifications, Pre-Modification Recorded Investment		0	0
Interest rate adjustment | Agricultural real estate
Loans and Leases Receivable, Troubled Debt Restructuring
Financing Receivable, Modifications, Pre-Modification Recorded Investment			188
Interest rate adjustment | Total real estate loans
Loans and Leases Receivable, Troubled Debt Restructuring
Financing Receivable, Modifications, Pre-Modification Recorded Investment		84	13,971
Interest rate adjustment | Total consumer loans
Loans and Leases Receivable, Troubled Debt Restructuring
Financing Receivable, Modifications, Pre-Modification Recorded Investment		0	27
Interest rate adjustment | Indirect consumer
Loans and Leases Receivable, Troubled Debt Restructuring
Financing Receivable, Modifications, Pre-Modification Recorded Investment	0
Interest rate adjustment | Commercial
Loans and Leases Receivable, Troubled Debt Restructuring
Financing Receivable, Modifications, Pre-Modification Recorded Investment	3,318	0	265
Other Concession [Member]
Loans and Leases Receivable, Troubled Debt Restructuring
Financing Receivable, Modifications, Pre-Modification Recorded Investment	513	1,092	2,476
Other Concession [Member] | Commercial real estate
Loans and Leases Receivable, Troubled Debt Restructuring
Financing Receivable, Modifications, Pre-Modification Recorded Investment	54	1,047	2,310
Other Concession [Member] | Land acquisition & development construction real estate
Loans and Leases Receivable, Troubled Debt Restructuring
Financing Receivable, Modifications, Pre-Modification Recorded Investment			0
Other Concession [Member] | Residential construction real estate
Loans and Leases Receivable, Troubled Debt Restructuring
Financing Receivable, Modifications, Pre-Modification Recorded Investment			0
Other Concession [Member] | Total construction loans
Loans and Leases Receivable, Troubled Debt Restructuring
Financing Receivable, Modifications, Pre-Modification Recorded Investment			0
Other Concession [Member] | Residential real estate
Loans and Leases Receivable, Troubled Debt Restructuring
Financing Receivable, Modifications, Pre-Modification Recorded Investment		15	79
Other Concession [Member] | Agricultural real estate
Loans and Leases Receivable, Troubled Debt Restructuring
Financing Receivable, Modifications, Pre-Modification Recorded Investment			0
Other Concession [Member] | Total real estate loans
Loans and Leases Receivable, Troubled Debt Restructuring
Financing Receivable, Modifications, Pre-Modification Recorded Investment		1,062	2,389
Other Concession [Member] | Total consumer loans
Loans and Leases Receivable, Troubled Debt Restructuring
Financing Receivable, Modifications, Pre-Modification Recorded Investment		0	0
Other Concession [Member] | Indirect consumer
Loans and Leases Receivable, Troubled Debt Restructuring
Financing Receivable, Modifications, Pre-Modification Recorded Investment	4
Other Concession [Member] | Commercial
Loans and Leases Receivable, Troubled Debt Restructuring
Financing Receivable, Modifications, Pre-Modification Recorded Investment	455	30	87
Extension of terms or maturity
Loans and Leases Receivable, Troubled Debt Restructuring
Financing Receivable, Modifications, Pre-Modification Recorded Investment	9,317	785	9,980
Extension of terms or maturity | Commercial real estate
Loans and Leases Receivable, Troubled Debt Restructuring
Financing Receivable, Modifications, Pre-Modification Recorded Investment	628	672	1,378
Extension of terms or maturity | Land acquisition & development construction real estate
Loans and Leases Receivable, Troubled Debt Restructuring
Financing Receivable, Modifications, Pre-Modification Recorded Investment			7,308
Extension of terms or maturity | Residential construction real estate
Loans and Leases Receivable, Troubled Debt Restructuring
Financing Receivable, Modifications, Pre-Modification Recorded Investment			408
Extension of terms or maturity | Total construction loans
Loans and Leases Receivable, Troubled Debt Restructuring
Financing Receivable, Modifications, Pre-Modification Recorded Investment			7,716
Extension of terms or maturity | Residential real estate
Loans and Leases Receivable, Troubled Debt Restructuring
Financing Receivable, Modifications, Pre-Modification Recorded Investment		0	708
Extension of terms or maturity | Agricultural real estate
Loans and Leases Receivable, Troubled Debt Restructuring
Financing Receivable, Modifications, Pre-Modification Recorded Investment			0
Extension of terms or maturity | Total real estate loans
Loans and Leases Receivable, Troubled Debt Restructuring
Financing Receivable, Modifications, Pre-Modification Recorded Investment		672	9,802
Extension of terms or maturity | Total consumer loans
Loans and Leases Receivable, Troubled Debt Restructuring
Financing Receivable, Modifications, Pre-Modification Recorded Investment		113	0
Extension of terms or maturity | Indirect consumer
Loans and Leases Receivable, Troubled Debt Restructuring
Financing Receivable, Modifications, Pre-Modification Recorded Investment	0
Extension of terms or maturity | Commercial
Loans and Leases Receivable, Troubled Debt Restructuring
Financing Receivable, Modifications, Pre-Modification Recorded Investment	$ 8,689	$ 0	$ 178

Loans - Schedule of Recorded77

Loans - Schedule of Recorded Investment in Criticized Loans by Class and Credit Quality Indicator (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	$ 5,193,321	$ 4,856,615
Commercial real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	1,793,258	1,639,422
Land acquisition & development construction real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	224,066	220,443
Residential construction real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	111,763	96,580
Commercial Construction
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	94,890	101,246
Total construction loans
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	430,719	418,269
Residential real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	1,032,851	999,903
Agricultural real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	156,234	167,659
Total real estate loans
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	3,413,062	3,225,253
Indirect consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	622,529	552,863
Other consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	153,717	144,141
Credit card consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	68,107	65,467
Commercial
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	792,416	740,073
Agricultural
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	142,151	124,859
Total consumer loans
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	844,353	762,471
Special Mention [Member]
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	127,270	154,084
Special Mention [Member] | Commercial real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	61,787	84,533
Special Mention [Member] | Land acquisition & development construction real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	16,593	11,826
Special Mention [Member] | Residential construction real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	1,640	2,029
Special Mention [Member] | Commercial Construction
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	166	39
Special Mention [Member] | Total construction loans
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	18,399	13,894
Special Mention [Member] | Residential real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	4,453	10,473
Special Mention [Member] | Agricultural real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	6,114	10,122
Special Mention [Member] | Total real estate loans
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	90,753	119,022
Special Mention [Member] | Indirect consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	644	916
Special Mention [Member] | Other consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	651	553
Special Mention [Member] | Credit card consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment		0
Special Mention [Member] | Commercial
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	32,975	25,766
Special Mention [Member] | Agricultural
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	2,247	7,827
Special Mention [Member] | Total consumer loans
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	1,295	1,469
Substandard [Member]
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	162,785	163,675
Substandard [Member] | Commercial real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	84,556	83,448
Substandard [Member] | Land acquisition & development construction real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	12,482	15,016
Substandard [Member] | Residential construction real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	1,886	2,666
Substandard [Member] | Commercial Construction
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	323	253
Substandard [Member] | Total construction loans
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	14,691	17,935
Substandard [Member] | Residential real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	9,661	10,848
Substandard [Member] | Agricultural real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	16,529	12,328
Substandard [Member] | Total real estate loans
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	125,437	124,559
Substandard [Member] | Indirect consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	1,131	1,590
Substandard [Member] | Other consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	1,130	1,085
Substandard [Member] | Credit card consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment		348
Substandard [Member] | Commercial
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	27,982	32,433
Substandard [Member] | Agricultural
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	7,105	3,660
Substandard [Member] | Total consumer loans
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	2,261	3,023
Doubtful [Member]
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	30,350	34,854
Doubtful [Member] | Commercial real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	10,609	15,246
Doubtful [Member] | Land acquisition & development construction real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	591	2,507
Doubtful [Member] | Residential construction real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	0	0
Doubtful [Member] | Commercial Construction
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	756	2,442
Doubtful [Member] | Total construction loans
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	1,347	4,949
Doubtful [Member] | Residential real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	2,540	1,121
Doubtful [Member] | Agricultural real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	0	612
Doubtful [Member] | Total real estate loans
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	14,496	21,928
Doubtful [Member] | Indirect consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	154	121
Doubtful [Member] | Other consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	198	432
Doubtful [Member] | Credit card consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment		1,263
Doubtful [Member] | Commercial
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	15,085	10,273
Doubtful [Member] | Agricultural
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	417	837
Doubtful [Member] | Total consumer loans
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	352	1,816
Total Criticized Loans [Member]
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	320,405	352,613
Total Criticized Loans [Member] | Commercial real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	156,952	183,227
Total Criticized Loans [Member] | Land acquisition & development construction real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	29,666	29,349
Total Criticized Loans [Member] | Residential construction real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	3,526	4,695
Total Criticized Loans [Member] | Commercial Construction
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	1,245	2,734
Total Criticized Loans [Member] | Total construction loans
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	34,437	36,778
Total Criticized Loans [Member] | Residential real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	16,654	22,442
Total Criticized Loans [Member] | Agricultural real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	22,643	23,062
Total Criticized Loans [Member] | Total real estate loans
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	230,686	265,509
Total Criticized Loans [Member] | Indirect consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	1,929	2,627
Total Criticized Loans [Member] | Other consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	1,979	2,070
Total Criticized Loans [Member] | Credit card consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment		1,611
Total Criticized Loans [Member] | Commercial
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	76,042	68,472
Total Criticized Loans [Member] | Agricultural
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	9,769	12,324
Total Criticized Loans [Member] | Total consumer loans
Loans and Leases Receivable Recorded Investment, Criticized Loans
Loans held for investment	$ 3,908	$ 6,308

Schedule of Allowance for Loan

Schedule of Allowance for Loan Losses by Portfolio Segment (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Financing Receivable, Allowance for Credit Losses
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Allowance for Loan Losses				$ 382	$ 287
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	$ 74,200	$ 85,339	$ 100,511
Provision charged to operating expense	6,822	(6,622)	(6,125)
Less loans charged-off	(11,637)	(13,995)	(20,513)
Add back recoveries of loans previously charged-off	7,432	9,478	11,466
Ending balance	76,817	74,200	85,339
Allowance for loan losses:
Loans individually evaluated for impairment				11,575	5,792	$ 8,929
Loans collectively evaluated for impairment				65,242	68,408	76,410
Ending balance	74,200	85,339	100,511	76,817	74,200	85,339
Total loans:
Individually evaluated for impairment				91,965	78,480	110,572
Individually evaluated for impairment				5,101,356	4,778,135	4,193,420
Total Loans				5,193,321	4,856,615	4,303,992
Real Estate
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	53,884	63,923	75,782
Provision charged to operating expense	(645)	(10,348)	(7,722)
Less loans charged-off	(4,076)	(3,014)	(10,224)
Add back recoveries of loans previously charged-off	3,133	3,323	6,087
Ending balance	52,296	53,884	63,923
Allowance for loan losses:
Loans individually evaluated for impairment				4,794	3,961	7,339
Loans collectively evaluated for impairment				47,502	49,923	56,584
Ending balance	53,884	63,923	75,782	52,296	53,884	63,923
Total loans:
Individually evaluated for impairment				66,516	62,775	96,862
Individually evaluated for impairment				3,346,546	3,162,478	2,745,393
Total Loans				3,413,062	3,225,253	2,842,255
Consumer
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	5,035	6,193	7,141
Provision charged to operating expense	3,243	1,382	1,605
Less loans charged-off	(5,683)	(4,887)	(4,612)
Add back recoveries of loans previously charged-off	2,549	2,347	2,059
Ending balance	5,144	5,035	6,193
Allowance for loan losses:
Loans individually evaluated for impairment				0	0	0
Loans collectively evaluated for impairment				5,144	5,035	6,193
Ending balance	5,035	6,193	7,141	5,144	5,035	6,193
Total loans:
Individually evaluated for impairment				0	0	0
Individually evaluated for impairment				844,353	762,471	671,587
Total Loans				844,353	762,471	671,587
Commercial
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	14,307	14,747	17,085
Provision charged to operating expense	4,376	1,809	41
Less loans charged-off	(1,657)	(6,030)	(5,672)
Add back recoveries of loans previously charged-off	1,749	3,781	3,293
Ending balance	18,775	14,307	14,747
Allowance for loan losses:
Loans individually evaluated for impairment				6,487	1,190	1,504
Loans collectively evaluated for impairment				12,288	13,117	13,243
Ending balance	14,307	14,747	17,085	18,775	14,307	14,747
Total loans:
Individually evaluated for impairment				24,471	14,526	13,585
Individually evaluated for impairment				767,945	725,547	662,959
Total Loans				792,416	740,073	676,544
Agriculture
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	974	476	503
Provision charged to operating expense	(152)	535	(49)
Less loans charged-off	(221)	(64)	(5)
Add back recoveries of loans previously charged-off	1	27	27
Ending balance	602	974	476
Allowance for loan losses:
Loans individually evaluated for impairment				294	641	86
Loans collectively evaluated for impairment				308	333	390
Ending balance	974	476	503	602	974	476
Total loans:
Individually evaluated for impairment				978	1,179	125
Individually evaluated for impairment				141,173	123,680	111,747
Total Loans				142,151	124,859	111,872
Other
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	0	0	0
Provision charged to operating expense	0	0	0
Less loans charged-off	0	0	0
Add back recoveries of loans previously charged-off	0	0	0
Ending balance	0	0	0
Allowance for loan losses:
Loans individually evaluated for impairment				0	0	0
Loans collectively evaluated for impairment				0	0	0
Ending balance	$ 0	$ 0	$ 0	0	0	0
Total loans:
Individually evaluated for impairment				0	0	0
Individually evaluated for impairment				1,339	3,959	1,734
Total Loans				$ 1,339	$ 3,959	$ 1,734

Premises and Equipment (Details

Premises and Equipment (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Property, Plant and Equipment
Premises and equipment, gross	$ 332,674	$ 324,907
Less accumulated depreciation	(141,862)	(129,695)
Premises and equipment, net	190,812	195,212
Land
Property, Plant and Equipment
Premises and equipment, gross	37,999	40,620
Buildings and improvements
Property, Plant and Equipment
Premises and equipment, gross	213,321	209,328
Furniture and equipment
Property, Plant and Equipment
Premises and equipment, gross	$ 81,354	$ 74,959

Company - Owned Life Insuranc80

Company - Owned Life Insurance (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Schedule of Company - Owned Life Insurance, By Type
Company owned life insurance	$ 187,253	$ 153,821
Key executive, principal shareholder
Schedule of Company - Owned Life Insurance, By Type
Cash surrender value of life insurance	3,926	3,798
Key executive split dollar
Schedule of Company - Owned Life Insurance, By Type
Cash surrender value of life insurance	4,778	4,707
Group life
Schedule of Company - Owned Life Insurance, By Type
Cash surrender value of life insurance	178,549
FIB | Group life
Schedule of Company - Owned Life Insurance, By Type
Cash surrender value of life insurance	$ 178,549	$ 145,316

Other Real Estate Owned (Detail

Other Real Estate Owned (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Real Estate Acquired Through Foreclosure [Roll Forward]
Balance at beginning of year	$ 13,554	$ 15,504	$ 32,571
Acquisitions	0	3,608	0
Real Estate Acquired Through Foreclosure, Additions	5,560	5,198	11,545
Capitalized improvements	0	0	65
Valuation adjustments	(207)	(224)	(3,512)
Dispositions	(12,653)	(10,532)	(25,165)
Balance at end of year	6,254	13,554	15,504
Valuation adjustments	(207)	(224)	(3,512)
Write-down due to change in appraised value	106	93	1,083
Write-down due to change in management estimates	$ 101	$ 131	$ 2,429

Derivatives and Hedging (Detail

Derivatives and Hedging (Details) - USD ($) $ in Thousands	Sep. 22, 2015	Dec. 31, 2015	Dec. 31, 2014
Derivative [Line Items]
Derivative, Inception Date	Sep. 22, 2015
Derivative Liability, Notional Amount	$ 100,000	$ 100,000
Derivative, Fixed Interest Rate	1.94%
Designated as Hedging Instrument [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative Instruments, Loss Recognized in Other Comprehensive Income (Loss), Effective Portion		165	$ 0
Derivative Liability, Notional Amount		100,000	0
Interest Rate Derivative Liabilities, at Fair Value		165	0
Not Designated as Hedging Instrument [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative Liability, Notional Amount		9,369	3,200
Interest Rate Derivative Liabilities, at Fair Value		829	59
Derivative Asset, Notional Amount		9,369	3,200
Interest Rate Derivative Assets, at Fair Value		788	61
Derivative, Loss on Derivative		$ (43)	$ (2)

Mortgage Servicing Rights - At

Mortgage Servicing Rights - At Amortized Cost (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2015USD ($)	Dec. 31, 2014USD ($)	Dec. 31, 2013USD ($)
Servicing Asset at Amortized Value, Balance [Roll Forward]
Servicing asset at fair value, ending	$ 15,621	$ 14,038
Mortgage loans
Servicing Asset at Amortized Value, Balance [Roll Forward]
Servicing asset at amortized cost, before valuation reserve, beginning	14,374	14,018	$ 13,224
Servicing Asset at Amortized Cost, Acquisitions	306	0	0
Originations of mortgage servicing rights	3,614	2,717	3,581
Amorization expense	(2,434)	(2,361)	(2,787)
Servicing asset at amortized cost, before valuation reserve, ending	15,860	14,374	14,018
Less valuation reserve	(239)	(336)	(472)
Servicing asset at fair value, ending	15,621	14,038	13,546
Principal balance of serviced loans underlying mortgage servicing rights	$ 2,906,239	$ 2,615,311	$ 2,416,621
Mortgage servicing rights as a percentage of serviced loans	0.0054	0.0054	0.0056

Mortgage Servicing Rights - 84

Mortgage Servicing Rights - At Fair Value (Details) - Mortgage loans $ in Thousands	12 Months Ended
	Dec. 31, 2015USD ($)
Servicing Assets and Servicing Liabilities at Fair Value, Assumptions Used to Estimate Fair Value [Abstract]
Mortagage servicing rights, fair value	$ 31,011
Servicing asset at fair value, assumptions used to estimate fair value, weighted average life	7 years 3 months 17 days
Minimum
Servicing Assets and Servicing Liabilities at Fair Value, Assumptions Used to Estimate Fair Value [Abstract]
Servicing assets at fair value, assumptions used to estimate fair value, discount rate	9.80%
Servicing assets at fair value, assumptions used to estimate fair value, prepayment speed	0.50%
Maximum
Servicing Assets and Servicing Liabilities at Fair Value, Assumptions Used to Estimate Fair Value [Abstract]
Servicing assets at fair value, assumptions used to estimate fair value, discount rate	14.50%
Servicing assets at fair value, assumptions used to estimate fair value, prepayment speed	1.80%

Mortgage Servicing Rights - Va

Mortgage Servicing Rights - Valuation of Impairment (Details) - Mortgage loans - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Valuation Allowance for Impairment of Recognized Servicing Assets
Impairment reversals	$ 97	$ 136	$ 99
Permanent impairment charged against carrying value	$ 0	$ 0	$ 0

Deposits (Details)

Deposits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Deposits [Abstract]
Interest-bearing Domestic Deposit, Brokered	$ 0	$ 0
Deposits, by Type [Abstract]
Non-interest bearing demand	1,823,716	1,791,364
Interest bearing:
Demand	2,178,373	2,133,273
Savings	1,955,256	1,843,355
Time, $100 and over	487,372	520,125
Time, other	644,220	718,095
Total interest bearing	5,265,221	5,214,848
Total deposits	7,088,937	7,006,212
Time deposits obtained through Certificate of Deposit Account Registry Service (CDARS)	38,336	40,491
Contractual Maturities, Time Deposits, $100,000 or More [Abstract]
2015, Time, $100 and Over	109,343
2016, Time, $100 and Over	82,059
2017, Time, $100 and Over	131,381
2018, Time, $100 and Over	164,589
Time Deposits, $100,000 or More	487,372	520,125
Time Deposits, Fiscal Year Maturity [Abstract]
2015, Time	309,819
2016, Time	161,333
2017, Time	266,174
2018, Time	394,266
Time Deposits	1,131,592
Interest expense, time deposits, $100,000 or more	3,739	4,003	$ 4,880
Time Deposits, $250,000 or More	222,912	$ 228,410
FDIC Deposit Insurance Limit	$ 250

Long-Term Debt and Other Borr87

Long-Term Debt and Other Borrowed Funds (Details) - USD ($)	1 Months Ended	9 Months Ended
	Feb. 29, 2008	Sep. 30, 2015	Dec. 31, 2015	Dec. 31, 2014	Feb. 28, 2008	Jan. 10, 2008
Debt Instrument
Long-term debt and capital lease obligations			$ 27,885,000	$ 38,067,000
Fiscal Year Maturities of Long-term Debt
2,015			65,000
2,016			71,000
2,017			20,077,000
2,018			83,000
2,019			90,000
Thereafter			7,499,000
Long-term debt and capital lease obligations			27,885,000	38,067,000
Debt Instrument, Issuance Date		Jan. 29, 2015
Unamortized Debt Issuance Expense			7,000
Other borrowings			2,000	9,000
Debt Instrument, Maturity Date		Jul. 29, 2022
Parent Company
Debt Instrument
Long-term debt			20,000,000	20,000,000
Subordinated Debt | Subordinated Term Loan, 6.81% | Parent Company
Debt Instrument
Long-term debt			$ 20,000,000	20,000,000
Fiscal Year Maturities of Long-term Debt
Debt instrument, face amount						$ 20,000,000
Debt instrument, interest rate, stated percentage			6.81%			6.81%
Subordinated Debt | Subordinated Term Loan, Variable Rate | Subsidiaries
Debt Instrument
Long-term debt			$ 0	15,000,000
Fiscal Year Maturities of Long-term Debt
Debt instrument, face amount					$ 15,000,000
Debt instrument, interest rate at period end			2.24%
Subordinated Debt | Subordinated Term Loan, Variable Rate | Subsidiaries | LIBOR
Fiscal Year Maturities of Long-term Debt
Debt instrument, basis spread on variable rate	2.00%
Subordinated Debt | Note Payable, 6.24% | Parent Company
Fiscal Year Maturities of Long-term Debt
Debt instrument, interest rate, stated percentage						6.24%
Notes Payable to Banks | Notes Payable to FHLB | Subsidiaries
Debt Instrument
Long-term debt			$ 0	225,000
Fiscal Year Maturities of Long-term Debt
FHLB, advances, weighted average interest rate			4.86%
Capital Lease Obligations | Capital Lease Obligation, 8.00% | Subsidiaries
Debt Instrument
Capital Lease Obligations			$ 1,582,000	1,643,000
Fiscal Year Maturities of Long-term Debt
Debt instrument, interest rate, stated percentage			8.00%
Federal Home Loan Bank | Notes Payable to FHLB | Subsidiaries
Fiscal Year Maturities of Long-term Debt
FHLB, advances, maximum amount available			$ 752,639,000
Long-term FHLB advances				225,000
Federal Funds Purchased
Fiscal Year Maturities of Long-term Debt
Line of credit facility, maximum borrowing capacity			165,000,000
Federal Reserve Bank Advances
Fiscal Year Maturities of Long-term Debt
Line of credit facility, maximum borrowing capacity			407,739,000
Notes Payable, Other Payables [Member] | Note Payable, 6.24% | Subsidiaries
Debt Instrument
Long-term debt			1,343,000	1,199,000
Fiscal Year Maturities of Long-term Debt
Debt instrument, face amount			1,343,000
Notes Payable, Other Payables [Member] | Note Payable, 2.24% | Subsidiaries
Debt Instrument
Long-term debt			$ 4,960,000	$ 0
Secured Debt [Member]
Fiscal Year Maturities of Long-term Debt
Debt instrument, face amount		$ 4,960,000
Debt instrument, interest rate, stated percentage		2.28%
Noncontrolling Interest, Ownership Percentage by Parent		99.90%

Subordinated Debentures Held 88

Subordinated Debentures Held by Subsidiary Trusts - Financial Insruments Subject to Mandatory Redemption (Details) - Trusts $ in Thousands	Dec. 31, 2015USD ($)
Trust Preferred Securities Subject to Mandatory Redemption
Financial Instruments Subject to Mandatory Redemption by Settlement Terms
Financial Instruments Subject to Mandatory Redemption, Settlement Terms, Share Value, Amount	$ 80,000
Common Stock Subject to Mandatory Redemption
Financial Instruments Subject to Mandatory Redemption by Settlement Terms
Financial Instruments Subject to Mandatory Redemption, Settlement Terms, Share Value, Amount	$ 2,477

Subordinated Debentures Held 89

Subordinated Debentures Held by Subsidiary Trusts - Subordinated Debentures (Details) $ in Thousands	Dec. 26, 2014USD ($)	Dec. 15, 2014USD ($)	Jan. 31, 2008USD ($)	Dec. 31, 2007USD ($)	Nov. 30, 2007USD ($)	Oct. 31, 2007USD ($)	Dec. 31, 2015USD ($)trusts	Dec. 31, 2014USD ($)
Subordinated Borrowing
Number of company sponsored wholly-owned business trusts | trusts							6
Subordinated debentures held by subsidiary trusts							$ 82,477	$ 82,477
First Interstate Statutory Trust II | Junior Subordinated Deferrable Interest Debentures Issued by FIST II
Subordinated Borrowing
Subordinated debentures held by subsidiary trusts						$ 10,310	$ 10,310	10,310
Debt instrument, interest rate at period end							2.58%
First Interstate Statutory Trust II | Junior Subordinated Deferrable Interest Debentures Issued by FIST II | LIBOR
Subordinated Borrowing
Debt instrument, basis spread on variable rate						2.25%
First Interstate Statutory Trust I | Junior Subordinated Deferrable Interest Debentures Issued by FIST I
Subordinated Borrowing
Subordinated debentures held by subsidiary trusts					$ 15,464		$ 15,464	15,464
Debt instrument, interest rate at period end							3.26%
First Interstate Statutory Trust I | Junior Subordinated Deferrable Interest Debentures Issued by FIST I | Debt Instrument, Redemption, At Issuance through Year Five
Subordinated Borrowing
Debt instrument, interest rate, stated percentage					7.50%
First Interstate Statutory Trust I | Junior Subordinated Deferrable Interest Debentures Issued by FIST I | LIBOR | Debt Instrument, Redemption, After Period Five
Subordinated Borrowing
Debt instrument, basis spread on variable rate					2.75%
First Interstate Statutory Trust III | Junior Subordinated Deferrable Interest Debentures Issued by FIST III
Subordinated Borrowing
Subordinated debentures held by subsidiary trusts				$ 20,619			$ 20,619	20,619
Debt instrument, interest rate at period end							2.91%
First Interstate Statutory Trust III | Junior Subordinated Deferrable Interest Debentures Issued by FIST III | Debt Instrument, Redemption, At Issuance through Year Five
Subordinated Borrowing
Debt instrument, interest rate, stated percentage				6.88%
First Interstate Statutory Trust III | Junior Subordinated Deferrable Interest Debentures Issued by FIST III | LIBOR | Debt Instrument, Redemption, After Period Five
Subordinated Borrowing
Debt instrument, basis spread on variable rate				2.40%
First Interstate Statutory Trust IV | Junior Subordinated Deferrable Interest Debentures Issued by FIST IV
Subordinated Borrowing
Subordinated debentures held by subsidiary trusts							$ 15,464	15,464
Debt instrument, interest rate at period end							3.03%
First Interstate Statutory Trust IV | Junior Subordinated Deferrable Interest Debentures Issued by FIST IV | LIBOR
Subordinated Borrowing
Debt instrument, basis spread on variable rate				2.70%
First Interstate Statutory Trust V | Junior Subordinated Deferrable Interest Debentures Issued by FIST V
Subordinated Borrowing
Subordinated debentures held by subsidiary trusts			$ 10,310				$ 10,310	10,310
Debt instrument, interest rate at period end							3.08%
First Interstate Statutory Trust V | Junior Subordinated Deferrable Interest Debentures Issued by FIST V | Debt Instrument, Redemption, At Issuance through Year Five
Subordinated Borrowing
Debt instrument, interest rate, stated percentage			6.78%
First Interstate Statutory Trust V | Junior Subordinated Deferrable Interest Debentures Issued by FIST V | LIBOR | Debt Instrument, Redemption, After Period Five
Subordinated Borrowing
Debt instrument, basis spread on variable rate			2.75%
First Interstate Statutory Trust VI | Junior Subordinated Deferrable Interest Debentures Issued by FIST VI
Subordinated Borrowing
Subordinated debentures held by subsidiary trusts			$ 10,310				$ 10,310	$ 10,310
Debt instrument, interest rate at period end							3.08%
First Interstate Statutory Trust VI | Junior Subordinated Deferrable Interest Debentures Issued by FIST VI | LIBOR
Subordinated Borrowing
Debt instrument, basis spread on variable rate			2.75%
Mountain West Trusts [Member] | Junior Subordinated Deferrable Interest Debenture Issues by MWFC [Member]
Subordinated Borrowing
Redemption price	$ 6,006	$ 14,433
Liquidation amount per security	1	1
Mandatory redemption of trust preferred securities	5,825	14,000
Capitalization of subsidiaries	$ 181	$ 433
Mountain West Trusts [Member] | Junior Subordinated Deferrable Interest Debenture Issues by MWFC [Member] | LIBOR
Subordinated Borrowing
Debt instrument, basis spread on variable rate	3.10%	1.85%
Trust Preferred Securities Subject to Mandatory Redemption | Mountain West Trusts [Member]
Subordinated Borrowing
Financial Instruments Subject to Mandatory Redemption, Settlement Terms, Share Value, Amount							$ 19,825
Common Stock Subject to Mandatory Redemption | Mountain West Trusts [Member]
Subordinated Borrowing
Financial Instruments Subject to Mandatory Redemption, Settlement Terms, Share Value, Amount							$ 614

Capital Stock and Dividend Re90

Capital Stock and Dividend Restrictions (Details) - USD ($) $ / shares in Units, $ in Thousands	Jul. 31, 2014	Sep. 30, 2015	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Apr. 03, 2015	Jan. 24, 2014
Preferred Stock
Nonvoting, noncumulative preferred stock, shares outstanding			0	0
Common Stock, Recapitalization
Common stock, shares authorized			200,000,000
Common Stock
Business Acquisition, Equity Interest Issued or Issuable, Value Assigned			$ 35,972
Payments for Repurchase of Common Stock			$ 20,647	$ 9,739	$ 448
Class B Common Stock
Common Stock, Recapitalization
Common stock, shares authorized			100,000,000
Common Stock, Voting Rights			5
Common Stock
Common stock, shares, outstanding			23,729,631	23,859,483
Class A Common Stock
Class of Stock
Stock Repurchased and Retired During Period, Weighted Average Price			$ 26.01
Common Stock, Recapitalization
Common stock, shares authorized			100,000,000
Common Stock, Voting Rights			1
Common Stock
Common stock, shares, outstanding			21,698,594	21,928,932
Business Acquisition, Equity Interest Issued or Issuable, Value Assigned	$ 35,972
Stock Repurchased and Retired During Period, Shares			765,875
Payments for Repurchase of Common Stock			$ 19,921
2015 Equity Compensation Plan [Member] | Class A Common Stock
Class of Stock
Additional Shares Authorized						2,000,000
Amendment to 2006 Equity Compensation Plan [Domain] | Class A Common Stock
Class of Stock
Additional Shares Authorized							1,500,000
Mountain West Bank | Class A Common Stock
Common Stock
Business Acquisition, Equity Interest Issued or Issuable, Number of Shares	1,378,230		1,378,230
Board of Directors [Member]
Common Stock
Share-based Compensation Arrangement by Share-based Payment Award, Aggregate Value of Shares Issued		$ 591		$ 620
Board of Directors [Member] | Class A Common Stock
Common Stock
Share-based Compensation Arrangement by Share-based Payment Award, Shares Issued in Period		21,414		24,581

Earnings per Common Share Compu

Earnings per Common Share Computation of Basic and Diluted Earnings per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Net Income (Loss) Available to Common Stockholders, Basic [Abstract]
Net income	$ 86,795	$ 84,401	$ 86,136
Weighted Average Number of Shares Outstanding, Basic and Diluted [Abstract]
Weighted average common shares outstanding for basic earnings per share computation	45,184,091	44,615,060	43,566,681
Dilutive effect of stock-based compensation	462,327	595,501	477,921
Weighted average common shares outstanding for diluted earnings per common share computation	45,646,418	45,210,561	44,044,602
Earnings Per Share, Basic and Diluted [Abstract]
Basic earnings per common share (in dollars per share)	$ 1.92	$ 1.89	$ 1.98
Diluted earnings per common share (in dollars per share)	$ 1.90	$ 1.87	$ 1.96
Stock Options
Earnings Per Share, Basic and Diluted [Abstract]
Antidilutive securities excluded from computation of earnings per share (in shares)	12,890	5,000	21,372
Performance Shares [Member]
Earnings Per Share, Basic and Diluted [Abstract]
Antidilutive securities excluded from computation of earnings per share (in shares)	142,512	88,797	37,734

Regulatory Capital Schedule of

Regulatory Capital Schedule of Actual Capital Amounts and Ratios and Selected Minimum Regulatory Thresholds (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Total risk-based capital:
Actual Amount	$ 946,156	$ 897,769
Actual Ratio	15.40%	16.20%
Capital Required for Capital Adequacy under Basel III Phase-in Schedule	$ 492,692
Capital Required for Capital Adequacy under Basel III Phase-in Schedule to Risk Weighted Assets	8.00%
Adequately Capitalized Amount	$ 646,658
Adequately Capitalized Ratio	10.50%
Well Capitalized Amount	$ 615,865	$ 555,856
Well Capitalized Ratio	10.00%	10.00%
Tier 1 risk-based capital:
Actual Amount	$ 861,339	$ 807,229
Actual Ratio	14.00%	14.50%
Tier One Risk Based Capital under Basel III Phase-in Schedule	$ 369,519
Tier One Capital Required for Capital Adequacy under Basel III Phase-in Schedule to Risk Weighted Assets	6.00%
Adequately Capitalized Amount	$ 523,485
Adequately Capitalized Ratio	8.50%
Well Capitalized Amount	$ 492,692	$ 333,514
Well Capitalized Ratio	8.00%	6.00%
Common Equity Tier One Risked Based Capital	$ 781,339
Common Equity Tier One Risk Based Capital to Risk Weighted Assets	12.70%
Common Equity Tier One Capital Required for Capital Adequacy under Basel III Phase-in Schedule	$ 383,040
Common Equity Tier One Capital Required for Capital Adequacy under Basel III Phase-in Schedule to Risk Weighted Assets	4.50%
Tier One Common Equity Capital Required for Capital Adequacy under Basel III Fully Phased-in	$ 595,840
Tier One Common Equity Capital Required for Capital Adequacy under Basel III Fully Phased-in to Risk Weighted Assets	7.00%
Common Equity Tier One Capital to be Well Capitalized	$ 400,312
Common Equity Tier One Capital to be Well Capitalized to Risk Weighted Assets	6.50%
Leverage capital ratio:
Tier One Leverage Capital	$ 861,339	$ 807,229
Actual Ratio	10.10%	9.60%
Adequately Capitalized Amount	$ 246,346	$ 335,897
Adequately Capitalized Ratio	4.00%	4.00%
Well Capitalized Amount	$ 425,600	$ 419,871
Well Capitalized Ratio	5.00%	5.00%
Capital Required for Capital Adequacy		$ 444,685
Capital Required for Capital Adequacy to Risk Weighted Assets		8.00%
Tier One Risk Based Capital Required for Capital Adequacy		$ 222,343
Tier One Risk Based Capital Required for Capital Adequacy to Risk Weighted Assets		4.00%
FIB
Total risk-based capital:
Actual Amount	$ 882,504	$ 832,907
Actual Ratio	14.40%	15.10%
Capital Required for Capital Adequacy under Basel III Phase-in Schedule	$ 490,866
Capital Required for Capital Adequacy under Basel III Phase-in Schedule to Risk Weighted Assets	8.00%
Adequately Capitalized Amount	$ 644,262
Adequately Capitalized Ratio	10.50%
Well Capitalized Amount	$ 613,582	$ 553,085
Well Capitalized Ratio	10.00%	10.00%
Tier 1 risk-based capital:
Actual Amount	$ 805,805	$ 754,708
Actual Ratio	13.10%	13.70%
Tier One Risk Based Capital under Basel III Phase-in Schedule	$ 368,149
Tier One Capital Required for Capital Adequacy under Basel III Phase-in Schedule to Risk Weighted Assets	6.00%
Adequately Capitalized Amount	$ 521,545
Adequately Capitalized Ratio	8.50%
Well Capitalized Amount	$ 490,866	$ 331,851
Well Capitalized Ratio	8.00%	6.00%
Common Equity Tier One Risked Based Capital	$ 805,805
Common Equity Tier One Risk Based Capital to Risk Weighted Assets	13.10%
Common Equity Tier One Capital Required for Capital Adequacy under Basel III Phase-in Schedule	$ 381,730
Common Equity Tier One Capital Required for Capital Adequacy under Basel III Phase-in Schedule to Risk Weighted Assets	4.50%
Tier One Common Equity Capital Required for Capital Adequacy under Basel III Fully Phased-in	$ 593,802
Tier One Common Equity Capital Required for Capital Adequacy under Basel III Fully Phased-in to Risk Weighted Assets	7.00%
Common Equity Tier One Capital to be Well Capitalized	$ 398,829
Common Equity Tier One Capital to be Well Capitalized to Risk Weighted Assets	6.50%
Leverage capital ratio:
Tier One Leverage Capital	$ 805,805	$ 754,708
Actual Ratio	9.50%	9.10%
Adequately Capitalized Amount	$ 245,433	$ 330,006
Adequately Capitalized Ratio	4.00%	4.00%
Well Capitalized Amount	$ 424,145	$ 412,507
Well Capitalized Ratio	5.00%	5.00%
Capital Required for Capital Adequacy		$ 442,468
Capital Required for Capital Adequacy to Risk Weighted Assets		8.00%
Tier One Risk Based Capital Required for Capital Adequacy		$ 221,234
Tier One Risk Based Capital Required for Capital Adequacy to Risk Weighted Assets		4.00%

Commitments and Contingencies

Commitments and Contingencies - Unrecorded Purchase Commitments (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Sep. 22, 2015
Unrecorded Unconditional Purchase Obligation
Derivative Liability, Notional Amount	$ 100,000	$ 100,000
Construction Contracts
Unrecorded Unconditional Purchase Obligation
Commitments to Purchase	$ 1,341

Commitments and Contingencies94

Commitments and Contingencies - Operating Lease Commitments (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Schedule of Future Minimum Rental Commitments
Operating leases, rent expense	$ 2,660	$ 1,190	$ 1,403
Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
2,015	2,203
2,016	2,049
2,017	1,675
2,018	1,487
2,019	1,349
Thereafter	8,655
Operating leases, future minimum payments due	17,418
Third Parties
Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
2,015	1,913
2,016	1,800
2,017	1,537
2,018	1,487
2,019	1,349
Thereafter	8,655
Operating leases, future minimum payments due	16,741
Related Partnership
Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
2,015	290
2,016	249
2,017	138
2,018	0
2,019	0
Thereafter	0
Operating leases, future minimum payments due	$ 677
Ownership percentage in partnership	50.00%

Commitments and Contingencies95

Commitments and Contingencies - Residential Mortgage Loans Sold with Recourse Obligations (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Obligation to repurchase loans sold
Loss Contingencies
Loss contingency, estimate of possible loss	$ 3,465	$ 4,486

Commitments and Contingencies L

Commitments and Contingencies Legal Proceedings (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Pending Litigation [Member] | Kelly Logging Inc. v. First Interstate Bank [Member]
Loss Contingencies
Litigation Settlement, Expense	$ 5,000	$ 4,000

Financial Instruments with Of97

Financial Instruments with Off-Balance Sheet Risk (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Entity Information
Credit Extension Commitments	$ 1,401,686	$ 1,415,119
Credit Extension Commitments, Beyond One Year	388,752	363,609
Standby Letters of Credit
Entity Information
Credit Extension Commitments	52,250	58,950
Unused Credit Card Lines
Entity Information
Credit Extension Commitments	$ 581,695	$ 476,752

Income Taxes - Schedule of Inc

Income Taxes - Schedule of Income Tax Exepnse (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Current:
Federal	$ 26,741	$ 34,941	$ 30,757
State	4,472	4,928	4,533
Total current	31,213	39,869	35,290
Deferred:
Federal	11,047	4,870	10,056
State	1,402	475	1,220
Total deferred	12,449	5,345	11,276
Total income tax expense	$ 43,662	$ 45,214	$ 46,566

Income Taxes - Reconciliation

Income Taxes - Reconciliation of Tax Expense at Effective Tax Rate (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Tax Disclosure [Abstract]
Effective income tax rate reconciliation, at federal statutory income tax rate	35.00%	35.00%	35.00%
Income Tax Expense, Continuing Operations Income Tax Reconciliation [Abstract]
Tax expense at the statutory tax rate	$ 45,660	$ 45,365	$ 46,446
Increase (decrease) in tax resulting from:
Tax-exempt income	(4,092)	(4,255)	(3,620)
State income tax, net of federal income tax benefit	3,791	3,541	3,741
Income Tax Credits and Adjustments	(2,249)	(313)	(353)
Other, net	552	876	352
Total income tax expense	$ 43,662	$ 45,214	$ 46,566

Income Taxes - Deferred Tax As

Income Taxes - Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Deferred tax assets:
Loans, principally due to allowance for loan losses	$ 28,999	$ 28,506
Deferred Costs, Leasing, Gross	596	719
Deferred Tax Assets, Tax Deferred Expense, Reserves and Accruals, Contingencies	108	1,785
Deferred Discounts, Finance Charges and Interest Included in Receivables	4,552	7,022
Deferred Tax Assets, Unrealized Losses on Trading Securities	2,093	2,728
Employee benefits	9,009	8,256
Other real estate owned write-downs and carrying costs	598	2,536
Deferred gain on sale of subsidiary	0	253
Deferred revenue on contract	1,087	481
Other	126	760
Deferred tax assets	47,168	53,046
Deferred tax liabilities:
Fixed assets, principally differences in bases and depreciation	(5,140)	(569)
Deferred Tax Liabilities, Unrealized Gains on Available For Sale Securities	(2,538)	(1,351)
Investment in joint venture partnership, principally due to differences in depreciation of partnership assets	(1,301)	(1,053)
Prepaid amounts	(1,139)	(1,385)
Government agency stock dividends	(2,442)	(2,407)
Goodwill and core deposit intangibles	(39,886)	(36,732)
Mortgage servicing rights	(4,422)	(4,144)
Other	(65)	(531)
Deferred tax liabilities	(56,933)	(48,172)
Net deferred tax assets (liabilities)		4,874
Deferred Tax Liabilities, Net	(9,765)
Income Taxes Payable, Current	$ 6,275	$ 4,693

Stock-Based Compensation - Wei

Stock-Based Compensation - Weighted-Average Assumptions Used in Option Pricing Model (Details) - Stock Option	12 Months Ended
	Dec. 31, 2013$ / shares
Schedule of Share-Based Compensation Award, Options, Fair Value Assumption Inputs
Weighted average grant date fair value of options granted (in dollars per share)	$ 3.54
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract]
Expected volatility	30.61%
Expected dividend yield	3.00%
Risk-free interest rate	0.88%
Expected life of options (in years)	5 years 6 months 7 days

Stock-Based Compensation - Sto

Stock-Based Compensation - Stock Options Activity Rollforward (Details)	12 Months Ended
	Dec. 31, 2015$ / sharesshares
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Outstanding options, beginning of year, number of shares | shares	1,748,032
Exercised, number of shares | shares	(350,438)
Forfeited, number of shares | shares	(10,216)
Outstanding options, end of year, number of shares | shares	1,387,378
Outstanding options exercisable, end of year, number of shares | shares	1,265,596
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Roll Forward]
Outstanding options, beginning of year, weighted average exercise price | $ / shares	$ 17.01
Exercised, weighted average exercise price | $ / shares	16.77
Forfeited, weighted average exercise price | $ / shares	16.82
Outstanding options, end of year, weighted average exercise price | $ / shares	17.06
Outstanding options exercisable, end of year, weighted average exercise price | $ / shares	$ 17.05
Outstanding options, end of year weighted average remaining contractual term	3 years 8 months 6 days
Outstanding options exercisable, end of year, weighted average remaining contractual term	3 years 7 months 22 days

Stock-Based Compensation - Non

Stock-Based Compensation - Non-Vested Stock Options Rollforward (Details)	12 Months Ended
	Dec. 31, 2015$ / sharesshares
Share-Based Compensation Arrangement by Share Based Payment Award, Options, Nonvested, Number of Shares [Roll Forward]
Nonvested stock options, beginning of year, number of shares | shares	355,022
Nonvested stock options, vested, number of shares | shares	(225,961)
Nonvested stock options, forfeited, number of shares | shares	(7,279)
Nonvested stock options, end of year, number of shares | shares	121,782
Share-Based Compensation Arrangement by Share Based Payment Award, Options, Nonvested, Weighted-Average Grant Date Fair Value [Roll Forward]
Nonvested stock options, beginning of period, weighted-average grant date fair value | $ / shares	$ 3.62
Nonvested stock options, vested, weighted-average grant date fair value | $ / shares	3.73
Nonvested stock options, forfeited, weighted-average grant date fair value | $ / shares	3.48
Nonvested stock options, end of period, weighted-average grant date fair value | $ / shares	$ 3.48

Stock-Based Compensation - Res

Stock-Based Compensation - Restricted Stock Activity Rollforward (Details) - Restricted Stock	12 Months Ended
	Dec. 31, 2015$ / sharesshares
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Restricted stock, beginning of year, number of shares | shares	248,399
Granted, number of shares | shares	169,577
Vested, number of shares | shares	(95,153)
Forfeited, number of shares | shares	(16,583)
Canceled, number of shares | shares	(2,601)
Restricted stock, end of year, number of shares | shares	303,639
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Roll Forward]
Restricted stock, beginning of year, weighted-average measurement date fair value | $ / shares	$ 21.16
Granted, weighted average grant date fair value | $ / shares	26.27
Vested, weighted average grant date fair value | $ / shares	18.65
Forfeited, weighted average grant date fair value | $ / shares	24.07
Cancelled, weighted average grant date fair value | $ / shares	17.22
Restricted stock, end of year, weighted-average measurement date fair value | $ / shares	$ 25.15

Stock-Based Compensation - Nar

Stock-Based Compensation - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award
Stock compensation expense	$ 3,959	$ 3,634	$ 2,936
Tax benefits from stock-based compensation	1,443	1,390	1,122
Stock Option
Share-based Compensation Arrangement by Share-based Payment Award
Stock compensation expense	481	905	1,390
Tax benefits from stock-based compensation	184	346	531
Intrinsic value of fully-vested stock options outstanding	15,218
Total intrinsic value of options exercised	3,931	7,363	7,108
Tax benefit realized from stock option exercises	1,504	2,594	1,963
Proceeds from stock options exercised	3,369	6,299	9,271
Common stock redeemed for payment of stock option exercises, aggregate value	2,507	6,829	8,721
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized	$ 52
Unrecognized compensation cost related to nonvested restricted stock to be recognized over weighted average period (in years)	1 month 13 days
Share-Based CompensationaArrangement By Share Based Payment Award, Options, Vested In Period, Fair Value	$ 843
Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award
Stock compensation expense	2,887	2,109	1,546
Tax benefits from stock-based compensation	$ 1,104	$ 807	$ 591
Unrecognized compensation cost related to nonvested restricted stock to be recognized over weighted average period (in years)	1 year 9 months 18 days
Stock issued during period, shares, restricted stock award	169,577
Unrecognized compensation cost related to nonvested restricted stock awards	$ 4,444
Restricted Stock | Upon Achievement of Performance Goals
Share-based Compensation Arrangement by Share-based Payment Award
Stock issued during period, shares, restricted stock award	78,378
Restricted Stock | Upon Achievement of Defined Return on Asset Performance Goals
Share-based Compensation Arrangement by Share-based Payment Award
Stock issued during period, shares, restricted stock award	26,126
Restricted Stock | Upon Achievement of Defined Return on Equity Performance Goals
Share-based Compensation Arrangement by Share-based Payment Award
Stock issued during period, shares, restricted stock award	26,126
Restricted Stock | Upon Achievement of Defined Total Return to Shareholder Goals
Share-based Compensation Arrangement by Share-based Payment Award
Stock issued during period, shares, restricted stock award	26,126
Restricted Stock | Upon One-Third Annual Anniversary
Share-based Compensation Arrangement by Share-based Payment Award
Stock issued during period, shares, restricted stock award	91,199
2006 Plan | Stock Option
Share-based Compensation Arrangement by Share-based Payment Award
Shares available for grant	1,987,379

Employee Benefit Plans - Profi

Employee Benefit Plans - Profit Sharing and Savings Plans (Details) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits
Eligibility requirement, service hours to be completed	20 hours
Deferred Profit Sharing
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits
Eligibility requirement, lesser of percent of compensation	100.00%
Eligibility requirement, lesser of annual contribution amount	$ 50,000
Eligibility requirement, requisite service period	3 years
Compensation expense	$ 727,000	$ 1,509,000	$ 1,555,000
Savings Plan, Employee Elected
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits
Compensation expense	4,683,000	$ 4,256,000	$ 4,067,000
Maximum annual contribution per employee, amount per dollar of employee contribution	$ 1.25
Maximum annual contribution per employee, percent	4.00%

Employee Benefit Plans - Postr

Employee Benefit Plans - Postretirement Healthcare Plan (Details) - Postretirement Healthcare Plan - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Defined Benefit Plan Disclosure
Minimum age requirement	55 years
Requisite service period	15 years
Unfunded benefit obligation	$ 3,921	$ 3,577
Net periodic benefit cost	$ 400	$ 400	$ 571
Assumptions used calculating net periodic benefit cost, discount rate	3.60%	3.60%
Assumptions used calculating net periodic benefit cost, rate of compensation increase	6.00%	6.50%
Defined Benefit Plan, Expected Future Benefit Payments, Fiscal Year Maturity [Abstract]
2,015	$ 163
2,016	194
2,017	219
2,018	254
2,019	295
2020 through 2024	1,500
Accumulated other comprehensive income (loss), before tax, related to the Plan	555
Accumulated other comprehensive income (loss), net of tax	378
Net acturarial loss, net of tax	255
Unamortized transition asset, net of tax	300
Estimated amount amortized from accumulated other comprehensive loss into net periodic benefit costs	$ 35

Other Comprehensive Income - C

Other Comprehensive Income - Comprehensive Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Change in net unrealized Gain during period:
Change in net unrealized gain during period, before tax amount	$ 5,863	$ 21,147	$ (52,949)
Change in net unrealized gain during period, tax expense (benefit)	2,307	8,321	(20,835)
Change in net unrealized gain during period, net of tax amount	3,556	12,826	(32,114)
Investment securities available-for-sale:
Reclassification adjustment for net gains included in net income, before tax amount	(137)	(61)	(1)
Reclassification adjustment for net, gains included in net income, tax expense (benefit)	(54)	(24)	0
Reclassification adjustment for net gains included in net income, net of tax amount	(83)	(37)	(1)
Unamortized Premium on Available-For-Sale Securities Transferred to Held-To-Maturity
Unamortized premium on available-to-sale securities transferred into held-for-maturity, before tax amount	(1,101)	(548)
Unamortized premium on available-to-sale securities transferred into held-for-maturity, tax expense (benefit)	(433)	(216)
Unamortized premium on available-to-sale securities transferred into held-for-maturity, net of tax amount	(668)	(332)
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, before Tax	165
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Tax	65
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Net of Tax	100
Change in net actuarial loss:
Change in net actuarial loss, before tax amount	58	1,731	137
Change in net actuarial loss, tax expense (benefit)	23	681	54
Change in net actuarial loss, net of tax amount	35	1,050	83
Other comprehensive income (Loss)
Other comprehensive income (loss), before tax	4,848	22,269	(52,813)
Total other comprehensive income, tax expense (benefit)	1,908	8,762	(20,781)
Other comprehensive income, net of tax	$ 2,940	$ 13,507	$ (32,032)

Other Comprehensive Income - A

Other Comprehensive Income - Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Net accumulated other comprehensive income:
Net unrealized gain on investment securities available-for-sale	$ 684	$ (2,121)
Net actuarial loss on defined benefit post-retirement benefit plans	(378)	(413)
Accumulated Other Comprehensive Income (Loss), Cumulative Changes in Net Gain (Loss) from Cash Flow Hedges, Effect Net of Tax	100	0
Net accumulated other comprehensive income	$ 406	$ (2,534)

Non-Cash Investing and Finan110

Non-Cash Investing and Financing Activities (Details) - USD ($) $ in Thousands	Jul. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Class of Stock
Business Acquisition, Equity Interest Issued or Issuable, Value Assigned		$ 35,972
Transferred loans to mortgage servicing assets		3,614	$ 2,717	$ 3,581
Transfer of premises and equipment pending disposal to other assets, book value		$ 1,805		$ 1,448
Class A Common Stock
Class of Stock
Business Acquisition, Equity Interest Issued or Issuable, Value Assigned	$ 35,972
Class A Common Stock | Mountain West Bank
Class of Stock
Business Acquisition, Equity Interest Issued or Issuable, Number of Shares	1,378,230	1,378,230

Non-Cash Investing and Finan111

Non-Cash Investing and Financing Activities Investment Type (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2013USD ($)
Tax Credit Investment [Member]
Net Investment Income [Line Items]
Transfer from Investments	$ 429

Condensed Financial Informat112

Condensed Financial Information (Parent Company Only) - Condensed Balance Sheets (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Condensed balance sheets:
Cash and cash equivalents	$ 780,457	$ 798,670
Investment in subsidiaries, at equity:
Other assets	78,074	73,495
Total assets	8,728,196	8,609,936
Subordinated debentures held by subsidiary trusts	82,477	82,477
Total liabilities	7,777,703	7,701,012
Stockholders’ equity	950,493	908,924	$ 801,581	$ 751,186
Total liabilities and stockholders’ equity	8,728,196	8,609,936
Parent Company
Condensed balance sheets:
Cash and cash equivalents	55,162	65,483
Investment in subsidiaries, at equity:
Equity method investments	977,221	938,799
Advances from subsidiaries, net	6,257	4,337
Other assets	39,668	29,335
Total assets	1,078,308	1,037,954
Other liabilities	25,338	26,553
Long-term debt	20,000	20,000
Subordinated debentures held by subsidiary trusts	82,477	82,477
Total liabilities	127,815	129,030
Stockholders’ equity	950,493	908,924
Total liabilities and stockholders’ equity	1,078,308	1,037,954
Bank subsidiary
Investment in subsidiaries, at equity:
Equity method investments	975,236	936,817
Nonbank subsidiaries
Investment in subsidiaries, at equity:
Equity method investments	$ 1,985	$ 1,982

Condensed Financial Informat113

Condensed Financial Information (Parent Company Only) - Condensed Statements of Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Condensed Financial Statements, Captions
Salaries and benefits	$ 101,451	$ 96,513	$ 94,002
Interest expense	18,060	18,606	20,695
Acquisition Expense	795	4,017	0
Earnings before income tax benefit	130,457	129,615	132,702
Income tax benefit	43,662	45,214	46,566
Net income	86,795	84,401	86,136
Parent Company
Condensed Financial Statements, Captions
Dividends from subsidiaries	70,000	58,900	71,400
Other interest income	23	42	34
Other income, primarily management fees from subsidiaries	13,207	12,166	12,809
Total income	83,230	71,108	84,243
Salaries and benefits	16,267	15,722	15,914
Interest expense	3,844	4,002	4,098
Acquisition Expense	795	4,017
Other operating expenses, net	9,920	7,512	7,546
Total expenses	30,826	31,253	27,558
Earnings before income tax benefit	52,404	39,855	56,685
Income tax benefit	(6,952)	(6,862)	(5,703)
Income before undistributed earnings of subsidiaries	59,356	46,717	62,388
Undistributed earnings of subsidiaries	27,439	37,684	23,748
Net income	$ 86,795	$ 84,401	$ 86,136

Condensed Financial Informat114

Condensed Financial Information (Parent Company Only) - Condensed Statements of Cash Flows (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Cash flows from operating activities:
Net income	$ 86,795	$ 84,401	$ 86,136
Adjustments to reconcile net income to cash provided by operating activities:
Depreciation and amortization	18,313	16,855	16,245
Write-down of equipment pending disposal	806	102	616
Deferred income tax expense (benefit)	12,449	5,345	11,276
Stock-based compensation expense	3,959	3,634	2,936
Tax benefits from stock-based compensation	1,443	2,193	1,898
Excess tax benefits from stock-based compensation	(1,184)	(2,205)	(2,031)
Net cash provided by operating activities	115,400	122,008	150,225
Cash flows from investing activities:
Payments to Acquire Businesses, Net of Cash Acquired	(1,636)	35,556	0
Net cash used in investing activities	(95,339)	(195,842)	(204,937)
Cash flows from financing activities:
Redemption of preferred stock	(16,538)	(48)	(243)
Repayment of junior subordinated debentures held by subsidiary trusts	0	(20,439)	0
Proceeds from issuance of common stock, net of stock issuance costs	3,369	6,299	9,814
Excess tax benefits from stock-based compensation	1,184	2,205	2,031
Purchase and retirement of common stock	(20,647)	(9,739)	(448)
Dividends paid to common stockholders	(36,290)	(28,626)	(17,909)
Net cash used in financing activities	(38,274)	337,677	(211,793)
Net change in cash and cash equivalents	(18,213)	263,843	(266,505)
Cash and cash equivalents at beginning of year	798,670	534,827	801,332
Cash and cash equivalents at end of year	780,457	798,670	534,827
Parent Company
Cash flows from operating activities:
Net income	86,795	84,401	86,136
Adjustments to reconcile net income to cash provided by operating activities:
Undistributed earnings of subsidiaries	(27,439)	(37,684)	(23,748)
Stock-based compensation expense	3,959	3,634	2,936
Tax benefits from stock-based compensation	1,443	2,193	1,898
Excess tax benefits from stock-based compensation	(1,184)	(2,205)	(2,031)
Other, net	(11,333)	8,991	(5,804)
Net cash provided by operating activities	52,241	59,330	59,387
Cash flows from investing activities:
Payments to Acquire Businesses, Net of Cash Acquired	(7,207)	(37,891)	0
Net cash used in investing activities	(7,207)	(37,891)	0
Cash flows from financing activities:
Net (decrease) increase in advances from nonbank subsidiaries	(2,021)	(10,632)	6,992
Redemption of preferred stock	0	0	(50,000)
Repayments of Long-term Debt	(950)	0	0
Repayment of junior subordinated debentures held by subsidiary trusts	0	(20,439)	0
Proceeds from issuance of common stock, net of stock issuance costs	3,369	6,001	9,814
Excess tax benefits from stock-based compensation	1,184	2,205	2,031
Purchase and retirement of common stock	(20,647)	(9,739)	(448)
Dividends paid to common stockholders	(36,290)	(28,626)	(17,909)
Net cash used in financing activities	(55,355)	(61,230)	(49,520)
Net change in cash and cash equivalents	(10,321)	(39,791)	9,867
Cash and cash equivalents at beginning of year	65,483	105,274	95,407
Cash and cash equivalents at end of year	$ 55,162	$ 65,483	$ 105,274

Schedule of Financial Assets an

Schedule of Financial Assets and Financial Liabilities Measured at Fair Value on a Recurring and Non-Recurring Basis (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Write-down due to change in management estimates	$ 101	$ 131	$ 2,429
Related Allowance	11,575	5,792	$ 8,929
Fair Value Measured on a Non-recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impairment of Long-Lived Assets to be Disposed of	857	702
Long-Lived Assets to be Disposed of, Fair Value	1,506	1,083
Long-Lived Assets to be Disposed of, Carrying Value	2,363	1,785
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value Measured on a Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities available-for-sale	0
Deferred Compensation Plan Assets	0	0
Deferred Compensation Liability, Current and Noncurrent	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value Measured on a Non-recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans	0	0
Other real estate owned	0	0
Long-lived assets to be disposed, fair value disclosure	0	0
Significant Other Observable Inputs (Level 2) | Fair Value Measured on a Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset	953	61
Derivative Liability	829	59
Deferred Compensation Plan Assets	10,149	10,312
Deferred Compensation Liability, Current and Noncurrent	10,149	10,312
Significant Other Observable Inputs (Level 2) | Fair Value Measured on a Non-recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans	0	0
Other real estate owned	0	0
Long-lived assets to be disposed, fair value disclosure	0	0
Significant Unobservable Inputs (Level 3) | Fair Value Measured on a Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities available-for-sale	0
Deferred Compensation Plan Assets	0	0
Deferred Compensation Liability, Current and Noncurrent	0	0
Significant Unobservable Inputs (Level 3) | Fair Value Measured on a Non-recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans	20,875	30,494
Other real estate owned	1,789	4,554
Long-lived assets to be disposed, fair value disclosure	1,506	1,083
Related Allowance	11,575	5,792
Impaired Financing Receivable, Related Allowance, Partial Loan Charge-Offs	10,229	8,760
US Treasury Notes Securities | Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value Measured on a Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities available-for-sale	0
US Treasury Notes Securities | Significant Other Observable Inputs (Level 2) | Fair Value Measured on a Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities available-for-sale	3,911
US Treasury Notes Securities | Significant Unobservable Inputs (Level 3) | Fair Value Measured on a Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities available-for-sale	0
Obligations of U.S. government agencies | Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value Measured on a Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities available-for-sale	0	0
Obligations of U.S. government agencies | Significant Other Observable Inputs (Level 2) | Fair Value Measured on a Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities available-for-sale	520,181	720,933
Obligations of U.S. government agencies | Significant Unobservable Inputs (Level 3) | Fair Value Measured on a Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities available-for-sale	0	0
U.S. agency residential mortgage-backed securities & collateralized mortgage obligations | Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value Measured on a Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities available-for-sale	0	0
U.S. agency residential mortgage-backed securities & collateralized mortgage obligations | Significant Other Observable Inputs (Level 2) | Fair Value Measured on a Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities available-for-sale	929,046	990,666
U.S. agency residential mortgage-backed securities & collateralized mortgage obligations | Significant Unobservable Inputs (Level 3) | Fair Value Measured on a Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities available-for-sale	0	0
Private mortgage-backed securities | Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value Measured on a Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities available-for-sale	0	0
Private mortgage-backed securities | Significant Other Observable Inputs (Level 2) | Fair Value Measured on a Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities available-for-sale	156	325
Private mortgage-backed securities | Significant Unobservable Inputs (Level 3) | Fair Value Measured on a Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities available-for-sale	0	0
Other Investments | Significant Other Observable Inputs (Level 2) | Fair Value Measured on a Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities available-for-sale	3,546
Estimated Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities available-for-sale	1,456,840	1,711,924
Derivative Asset	953	61
Derivative Liability	829	59
Deferred Compensation Plan Assets	10,149	10,312
Deferred Compensation Liability, Current and Noncurrent	10,149	10,312
Estimated Fair Value | Fair Value Measured on a Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Deferred Compensation Plan Assets	10,149	10,312
Deferred Compensation Liability, Current and Noncurrent	10,149	10,312
Estimated Fair Value | Fair Value Measured on a Non-recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans	20,875	30,494
Other real estate owned	1,789	4,554
Long-lived assets to be disposed, fair value disclosure	1,506	1,083
Estimated Fair Value | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities available-for-sale	0	0
Derivative Asset	0	0
Derivative Liability	0	0
Deferred Compensation Plan Assets	0	0
Deferred Compensation Liability, Current and Noncurrent	0	0
Estimated Fair Value | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities available-for-sale	1,456,840	1,711,924
Derivative Asset	953	61
Derivative Liability	829	59
Deferred Compensation Plan Assets	10,149	10,312
Deferred Compensation Liability, Current and Noncurrent	10,149	10,312
Estimated Fair Value | Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities available-for-sale	0	0
Derivative Asset	0	0
Derivative Liability	0	0
Deferred Compensation Plan Assets	0	0
Deferred Compensation Liability, Current and Noncurrent	0	0
Estimated Fair Value | Significant Unobservable Inputs (Level 3) | Fair Value Measured on a Non-recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans	20,875	30,494
Estimated Fair Value | US Treasury Notes Securities | Fair Value Measured on a Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities available-for-sale	3,911
Estimated Fair Value | Obligations of U.S. government agencies | Fair Value Measured on a Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities available-for-sale	520,181	720,933
Estimated Fair Value | U.S. agency residential mortgage-backed securities & collateralized mortgage obligations | Fair Value Measured on a Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities available-for-sale	929,046	990,666
Estimated Fair Value | Private mortgage-backed securities | Fair Value Measured on a Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities available-for-sale	156	325
Estimated Fair Value | Other Investments | Fair Value Measured on a Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities available-for-sale	3,546
Estimate of Fair Value, Fair Value Disclosure, Gain (Loss) [Member] | Fair Value Measured on a Non-recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans	(21,804)	(14,552)
Other real estate owned	(382)	(12,665)
Long-lived assets to be disposed, fair value disclosure	(857)	(702)
Carrying Amount
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities available-for-sale	1,456,840	1,711,924
Derivative Asset	953	61
Derivative Liability	829	829
Deferred Compensation Plan Assets	10,149	10,312
Deferred Compensation Liability, Current and Noncurrent	10,149	10,149
Carrying Amount | Significant Unobservable Inputs (Level 3) | Fair Value Measured on a Non-recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans	42,679	45,046
Interest Rate Swap [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value Measured on a Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset	0	0
Derivative Liability	0	0
Interest Rate Swap [Member] | Significant Unobservable Inputs (Level 3) | Fair Value Measured on a Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset	0	0
Derivative Liability	0	0
Interest Rate Swap [Member] | Estimated Fair Value | Fair Value Measured on a Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset	953	61
Derivative Liability	$ 829	$ 59

Fair Value Measurements Fair Va

Fair Value Measurements Fair Value Inputs, Quantitative Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Loan and Leases Receivable, Impaired Loans [Member] | Minimum | Market Approach Valuation Technique
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Discount Rate	(0.00%)	(0.00%)
Loan and Leases Receivable, Impaired Loans [Member] | Maximum | Market Approach Valuation Technique
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Discount Rate	(53.00%)	(51.00%)
Loan and Leases Receivable, Impaired Loans [Member] | Weighted Average | Market Approach Valuation Technique
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Discount Rate	(38.00%)	(19.00%)
Real Estate Acquired in Satisfaction of Debt | Minimum | Market Approach Valuation Technique
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Discount Rate	(2.00%)	(0.00%)
Real Estate Acquired in Satisfaction of Debt | Maximum | Market Approach Valuation Technique
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Discount Rate	(96.00%)	(50.00%)
Real Estate Acquired in Satisfaction of Debt | Weighted Average | Market Approach Valuation Technique
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Discount Rate	(19.00%)	(15.00%)
Asses to be Disposed of by Sale | Minimum | Market Approach Valuation Technique
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Discount Rate	(0.00%)	(0.00%)
Asses to be Disposed of by Sale | Maximum | Market Approach Valuation Technique
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Discount Rate	(9.00%)	(9.00%)
Asses to be Disposed of by Sale | Weighted Average | Market Approach Valuation Technique
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Discount Rate	(6.00%)	(5.00%)
Estimated Fair Value | Fair Value Measured on a Non-recurring Basis
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Impaired loans	$ 20,875	$ 30,494
Other real estate owned	1,789	4,554
Long-lived assets to be disposed, fair value disclosure	$ 1,506	$ 1,083

Schedule of Estimated Fair Valu

Schedule of Estimated Fair Values of Financial Instruments by Level of Valuation Inputs (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Financial assets:
Investment securities held-to-maturity	$ 607,550	$ 584,533
Carrying Amount
Financial assets:
Cash and cash equivalents	780,457	798,670
Investment securities available-for-sale	1,456,840	1,711,924
Investment securities held-to-maturity	600,665	575,186
Accrued interest receivable	27,729	27,063
Mortgage servicing rights	15,621	14,038
Net loans	5,169,379	4,823,243
Derivative Asset	953	61
Deferred Compensation Plan Assets	10,149	10,312
Total financial assets	8,061,793	7,960,497
Financial liabilities:
Total deposits, excluding time deposits	5,957,345	5,767,992
Time deposits	1,131,592	1,238,220
Securities sold under repurchase agreements	510,635	502,250
Other borrowed funds	2	9
Accrued interest payable	4,960	5,833
Long-term debt	27,885	38,067
Subordinated debentures held by subsidiary trusts	82,477	82,477
Derivative Liability	829	829
Deferred Compensation Liability, Current and Noncurrent	10,149	10,149
Total financial liabilities	7,725,874	7,645,826
Estimated Fair Value
Financial assets:
Cash and cash equivalents	780,457	798,670
Investment securities available-for-sale	1,456,840	1,711,924
Investment securities held-to-maturity	607,550	584,533
Accrued interest receivable	27,729	27,063
Mortgage servicing rights	31,011	21,434
Net loans	5,128,705	4,800,725
Derivative Asset	953	61
Deferred Compensation Plan Assets	10,149	10,312
Total financial assets	8,043,394	7,954,722
Financial liabilities:
Total deposits, excluding time deposits	5,975,345	5,767,992
Time deposits	1,137,289	1,244,324
Securities sold under repurchase agreements	510,635	502,250
Other borrowed funds	2	9
Accrued interest payable	4,960	5,833
Long-term debt	27,622	37,781
Subordinated debentures held by subsidiary trusts	74,969	75,734
Derivative Liability	829	59
Deferred Compensation Liability, Current and Noncurrent	10,149	10,312
Total financial liabilities	7,741,800	7,644,294
Quoted Prices in Active Markets for Identical Assets (Level 1) | Estimated Fair Value
Financial assets:
Cash and cash equivalents	780,457	798,670
Investment securities available-for-sale	0	0
Investment securities held-to-maturity	0	0
Accrued interest receivable	0	0
Mortgage servicing rights	0	0
Net loans	0	0
Derivative Asset	0	0
Deferred Compensation Plan Assets	0	0
Total financial assets	780,457	798,670
Financial liabilities:
Total deposits, excluding time deposits	5,975,345	5,767,992
Time deposits	0	0
Securities sold under repurchase agreements	0	0
Other borrowed funds	0	0
Accrued interest payable	0	0
Long-term debt	0	0
Subordinated debentures held by subsidiary trusts	0	0
Derivative Liability	0	0
Deferred Compensation Liability, Current and Noncurrent	0	0
Total financial liabilities	5,975,345	5,767,992
Significant Other Observable Inputs (Level 2) | Estimated Fair Value
Financial assets:
Cash and cash equivalents	0	0
Investment securities available-for-sale	1,456,840	1,711,924
Investment securities held-to-maturity	607,550	584,533
Accrued interest receivable	27,729	27,063
Mortgage servicing rights	31,011	21,434
Net loans	5,107,830	4,770,231
Derivative Asset	953	61
Deferred Compensation Plan Assets	10,149	10,312
Total financial assets	7,242,062	7,125,558
Financial liabilities:
Total deposits, excluding time deposits	0	0
Time deposits	1,137,289	1,244,324
Securities sold under repurchase agreements	510,635	502,250
Other borrowed funds	2	9
Accrued interest payable	4,960	5,833
Long-term debt	27,622	37,781
Subordinated debentures held by subsidiary trusts	74,969	75,734
Derivative Liability	829	59
Deferred Compensation Liability, Current and Noncurrent	10,149	10,312
Total financial liabilities	1,766,455	1,876,302
Significant Unobservable Inputs (Level 3) | Estimated Fair Value
Financial assets:
Cash and cash equivalents	0	0
Investment securities available-for-sale	0	0
Investment securities held-to-maturity	0	0
Accrued interest receivable	0	0
Mortgage servicing rights	0	0
Net loans	20,875	30,494
Derivative Asset	0	0
Deferred Compensation Plan Assets	0	0
Total financial assets	20,875	30,494
Financial liabilities:
Total deposits, excluding time deposits	0	0
Time deposits	0	0
Securities sold under repurchase agreements	0	0
Other borrowed funds	0	0
Accrued interest payable	0	0
Long-term debt	0	0
Subordinated debentures held by subsidiary trusts	0	0
Derivative Liability	0	0
Deferred Compensation Liability, Current and Noncurrent	0	0
Total financial liabilities	$ 0	$ 0

Related Party Transactions (Det

Related Party Transactions (Details) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2015USD ($)director$ / sharesshares	Dec. 31, 2014USD ($)	Dec. 31, 2013USD ($)
Shareholder
Related Party Transaction
Ownership percentage threshhold for related party	5.00%
Executive Officers, Directors, Shareholders Greater than Five Percent, and Related Entities and Individuals to Such Persons [Member]
Loans and Leases Receivable, Related Parties Disclosure [Abstract]
Loans and leases receivable, related parties	$ 33,008	$ 33,002
Loans and leases receivable, related parties, additions	7,400
Loans and leases receivable, related parties, collections	7,283
Loans and Leases Receivable, Related Parties, Period Increase (Decrease)	111
Director, Controlling Ownership Interest in Entity | Insurance Premiums
Loans and Leases Receivable, Related Parties Disclosure [Abstract]
Related party transaction, selling, general and administrative expenses from transactions with related party			$ 764
Board of Directors Chairman, Wholly-Owned Entity | Aircraft Usage and Related Activities
Loans and Leases Receivable, Related Parties Disclosure [Abstract]
Related party transaction, expenses from transactions with related party	332	306	309
Related party transactions, other revenues	$ 64	77	61
Entity Majority Owned by Shareholders and Directors
Loans and Leases Receivable, Related Parties Disclosure [Abstract]
Related party relationship, number of directors | director	6
Entity Majority Owned by Shareholders and Directors | Education, Communication, Strategic Enterprise Planning and Corporate Governance Consultation
Loans and Leases Receivable, Related Parties Disclosure [Abstract]
Related party transaction, expenses from transactions with related party	$ 210	255	224
Director, Wholly-Owned Entity | Construction Management and Adivsory Services
Loans and Leases Receivable, Related Parties Disclosure [Abstract]
Related party transaction, expenses from transactions with related party		$ 60	$ 60
Related party transaction, contractual agreement, amount	$ 180
Related party transaction, contractual agreement, percentage of contract price	4.00%
Related party transaction, contractual agreement, initial payment	$ 60
Class A Common Stock
Loans and Leases Receivable, Related Parties Disclosure [Abstract]
Stock Repurchased and Retired During Period, Shares | shares	765,875
Stock Repurchased and Retired During Period, Weighted Average Price | $ / shares	$ 26.01
Class A Common Stock | Director
Loans and Leases Receivable, Related Parties Disclosure [Abstract]
Stock Repurchased and Retired During Period, Shares | shares	37,615
Stock Repurchased and Retired During Period, Weighted Average Price | $ / shares	$ 24.96

Subsequent Events Subsequent Ev

Subsequent Events Subsequent Events (Details)	Jan. 21, 2016$ / shares
Subsequent Event [Member] | Common Class A Stoc
Subsequent Event [Line Items]
Dividends Payable, Amount Per Share	$ 0.22