First Interstate BancSystem (FIBK) 10-Q 2 May 14 2014 Q1 Quarterly report Financial data

Document_and_Entity_Informatio

Document and Entity Information	3 Months Ended
	Mar. 31, 2014
Entity Registrant Name	'FIRST INTERSTATE BANCSYSTEM INC
Entity Central Index Key	'0000860413
Current Fiscal Year End Date	'--12-31
Entity Filer Category	'Accelerated Filer
Document Type	'10-Q
Document Period End Date	31-Mar-14
Document Fiscal Year Focus	'2014
Document Fiscal Period Focus	'Q1
Amendment Flag	'false
Class A Common Stock	'
Entity Common Stock, Shares Outstanding	20,343,161
Class B Common Stock	'
Entity Common Stock, Shares Outstanding	24,046,934

Consolidated_Balance_Sheets_Un

Consolidated Balance Sheets (Unaudited) (USD $)	Mar. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Assets	'	'
Cash and due from banks	$143,041	$141,663
Federal funds sold	562	672
Interest bearing deposits in banks	466,928	392,492
Total cash and cash equivalents	610,531	534,827
Investment securities:	'	'
Available-for-sale	1,893,652	1,947,706
Held-to-maturity (estimated fair values of $205,443 and $205,926 at March 31, 2014 and December 31, 2013, respectively)	201,436	203,837
Total investment securities	2,095,088	2,151,543
Loans held for investment	4,326,367	4,303,992
Mortgage loans held for sale	38,471	40,861
Total loans	4,364,838	4,344,853
Less allowance for loan losses	81,371	85,339
Net loans	4,283,467	4,259,514
Premises and equipment, net of accumulated depreciation	179,942	179,690
Goodwill	183,673	183,673
Company-owned life insurance	138,027	122,175
Other real estate owned (OREO)	16,594	15,504
Accrued interest receivable	27,135	26,450
Mortgage servicing rights, net of accumulated amortization and impairment reserve	13,474	13,546
Deferred tax asset, net	3,895	12,154
Core deposit intangibles, net of accumulated amortization	4,165	4,519
Other assets	61,834	61,056
Total assets	7,617,825	7,564,651
Deposits:	'	'
Non-interest bearing	1,458,460	1,491,683
Interest bearing	4,676,677	4,642,067
Total deposits	6,135,137	6,133,750
Securities sold under repurchase agreements	488,898	457,437
Accounts payable and accrued expenses	43,808	47,523
Accrued interest payable	4,953	4,963
Long-term debt	36,905	36,917
Other borrowed funds	9	3
Subordinated debentures held by subsidiary trusts	82,477	82,477
Total liabilities	6,792,187	6,763,070
Stockholders' equity:	'	'
Nonvoting noncumulative preferred stock without par value; authorized 100,000 shares; no shares issued and outstanding as of March 31, 2014 or December 31, 2013	0	0
Common stock	286,553	285,535
Retained earnings	546,444	532,087
Accumulated other comprehensive income, net	-7,359	-16,041
Total stockholders' equity	825,638	801,581
Total liabilities and stockholders' equity	$7,617,825	$7,564,651

Consolidated_Balance_Sheets_Un1

Consolidated Balance Sheets (Unaudited) (Parenthetical) (USD $)	Mar. 31, 2014	Dec. 31, 2013
In Thousands, except Share data, unless otherwise specified
Investment securities:	'	'
Held-to-maturity, fair values	$205,443	$205,926
Stockholders' equity:	'	'
Nonvoting noncumulative preferred stock, par value	$0	$0
Nonvoting noncumulative preferred stock, authorized shares	100,000	100,000
Nonvoting noncumulative preferred stock, issued shares	0	0
Nonvoting noncumulative preferred stock, outstanding shares	0	0

Consolidated_Statements_of_Inc

Consolidated Statements of Income (Unaudited) (USD $)	3 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Interest income:	'	'
Interest and fees on loans	$53,718	$55,493
Interest and dividends on investment securities:	'	'
Taxable	7,640	8,046
Exempt from federal taxes	1,097	1,226
Interest on deposits in banks	231	298
Interest on federal funds sold	1	4
Total interest income	62,687	65,067
Interest expense:	'	'
Interest on deposits	3,424	4,355
Interest on securities sold under repurchase agreements	66	100
Interest on long-term debt	473	480
Interest on preferred stock pending redemption	0	159
Interest on subordinated debentures held by subsidiary trusts	588	696
Total interest expense	4,551	5,790
Net interest income	58,136	59,277
Provision for loan losses	-5,000	500
Net interest income after provision for loan losses	63,136	58,777
Non-interest income:	'	'
Other service charges, commissions and fees	9,156	8,256
Income from the origination and sale of loans	4,660	10,675
Investment Advisory, Management and Administrative Fees	4,455	4,134
Service charges on deposit accounts	3,875	4,068
Investment securities gains, net	71	8
Other income	1,889	1,678
Total non-interest income	24,106	28,819
Non-interest expense:	'	'
Salaries and wages	22,411	23,405
Employee benefits	8,313	8,175
Occupancy, net	4,239	4,026
Furniture and equipment	3,201	3,052
Outsourced technology services	2,300	2,157
OREO expense, net of income	-19	1,896
FDIC insurance premiums	1,116	1,377
Professional fees	1,370	1,127
Mortgage servicing rights amortization	600	839
Mortgage servicing rights impairment recovery	-45	-48
Core deposit intangibles amortization	354	354
Other expenses	10,498	10,325
Total non-interest expense	54,338	56,685
Income before income tax expense	32,904	30,911
Income tax expense	11,511	10,867
Net income	$21,393	$20,044
Basic earnings per common share	$0.49	$0.46
Diluted earnings per common share	$0.48	$0.46

Consolidated_Statements_of_Com

Consolidated Statements of Comprehensive Income (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Net income	$21,393	$20,044
Other comprehensive income (loss), before tax:	'	'
Change in net unrealized gains (losses) during period	14,351	-5,717
Reclassification adjustment for net gains included in income	-71	-8
Defined benefit post-retirement benefits plans:	'	'
Change in net actuarial loss	35	35
Other comprehensive income (loss), before tax	14,315	-5,690
Deferred tax benefit (expense) related to other comprehensive income	-5,633	2,239
Other comprehensive income (loss), net of tax	8,682	-3,451
Comprehensive income, net of tax	$30,075	$16,593

Consolidated_Statements_of_Cha

Consolidated Statements of Changes in Stockholders Equity (Unaudited) (USD $)	Total	Common stock	Retained earnings	Accumulated other comprehensive income
In Thousands, unless otherwise specified
Beginning Balance at Dec. 31, 2012	$751,186	$271,335	$463,860	$15,991
Comprehensive income:	'	'	'	'
Net income	20,044	0	20,044	0
Other comprehensive income, net of tax	-3,451	0	0	-3,451
Common stock transactions:	'	'	'	'
Common shares purchased and retired 124,867 and 25,677 in 2014 and 2013 respectively	-448	-448	0	0
Non-vested common shares issued 147,876 and 108,873 in 2014 and 2013 respectively	0	0	0	0
3,782 and 1,815 non-vested common shares forfeited in 2014 and 2013 respectively	0	0	0	0
215,805 and 243,238 stock options exercised, net of 152,131 and 87,933 shares tendered in payment of option price and income tax withholding amounts in 2014 and 2013 respectively	3,145	3,145	0	0
Tax benefit of stock-based compensation	202	202	0	0
Stock-based compensation expense	695	695	0	0
Ending Balance at Mar. 31, 2013	771,373	274,929	483,904	12,540
Beginning Balance at Dec. 31, 2013	801,581	285,535	532,087	-16,041
Comprehensive income:	'	'	'	'
Net income	21,393	0	21,393	0
Other comprehensive income, net of tax	8,682	0	0	8,682
Common stock transactions:	'	'	'	'
Common shares purchased and retired 124,867 and 25,677 in 2014 and 2013 respectively	-3,159	-3,159	0	0
Non-vested common shares issued 147,876 and 108,873 in 2014 and 2013 respectively	0	0	0	0
3,782 and 1,815 non-vested common shares forfeited in 2014 and 2013 respectively	0	0	0	0
215,805 and 243,238 stock options exercised, net of 152,131 and 87,933 shares tendered in payment of option price and income tax withholding amounts in 2014 and 2013 respectively	2,476	2,476	0	0
Tax benefit of stock-based compensation	989	989	0	0
Stock-based compensation expense	712	712	0	0
Cash dividends declared:	'	'	'	'
Common ($0.16) per share in 2014	-7,036	0	-7,036	0
Ending Balance at Mar. 31, 2014	$825,638	$286,553	$546,444	($7,359)

Consolidated_Statements_of_Cha1

Consolidated Statements of Changes in Stockholders Equity (Unaudited) (Parenthetical) (USD $)	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Common stock	'	'
Common stock transactions:	'	'
Common shares purchased and retired	124,867	25,677
Common shares issued	0	0
Non-vested common shares issued	147,876	108,873
Non-vested common shares forfeited	3,782	1,815
Stock options exercised	215,805	243,238
Shares tendered in payment of option price and income tax withholding amounts	152,131	87,933
Retained earnings	'	'
Cash dividends declared:	'	'
Common (in dollars per share)	0.16	0

Consolidated_Statements_of_Cas

Consolidated Statements of Cash Flows (Unaudited) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Cash flows from operating activities:	'	'
Net income	$21,393	$20,044
Adjustments to reconcile net income to net cash provided by operating activities:	'	'
Provision for loan losses	-5,000	500
Net (gain) loss on disposal of property and equipment	-13	-20
Depreciation and amortization	3,896	4,203
Net premium amortization on investment securities	3,371	4,082
Net gains on investment securities transactions	-71	-8
Net gains on sales of mortgage loans held for sale	-3,323	-7,898
Net gain on sale of OREO	-435	-820
OREO valuation adjustments	0	2,305
Net impairment (reversal of impairment) of mortgage servicing rights	-45	-48
Deferred income tax expense	2,630	1,853
Net increase in cash surrender value of company-owned life insurance policies	-852	-429
Stock-based compensation expense	712	695
Tax benefits from stock-based compensation expense	989	202
Excess tax benefits from stock-based compensation	-982	-165
Originations of loans held for sale	151,911	371,684
Proceeds from sales of loans held for sale	157,141	389,437
Changes in operating assets and liabilities:	'	'
Increase in interest receivable	-685	-506
Decrease in other assets	-1,083	-64
Decrease in accrued interest payable	-10	-69
Decrease in accounts payable and accrued expenses	-3,694	-1,861
Net cash provided by operating activities	22,028	39,749
Cash flows from investing activities:	'	'
Purchases of held-to-maturity investment securities	0	-6,347
Purchases of available-for-sale investment securities	-95,077	-227,040
Proceeds from maturities and paydowns of held-to-maturity investment securities	2,185	3,512
Proceeds from maturities and paydowns of available-for-sale investment securities	160,337	201,621
Purchases of company-owned life insurance	-15,000	0
Proceeds from sales of mortgage servicing rights	266	311
Extensions of credit to customers, net of repayments	-28,580	-22,997
Recoveries of loans charged-off	3,822	2,913
Proceeds from sales of OREO	2,760	3,957
Capital contribution to unconsolidated equity method investee	-3,142	-650
Net cash used in investing activities	27,571	-44,720
Cash flows from financing activities:	'	'
Net increase (decrease) in deposits	1,387	-212,066
Net decrease in repurchase agreements	31,461	-38,580
Net increase (decrease) in short-term borrowings	6	-24
Repayments of long-term debt	-12	-10
Redemption of preferred stock	0	-50,000
Proceeds from issuance of common stock	2,476	3,145
Excess tax benefits from stock-based compensation	982	165
Purchase and retirement of common stock	-3,159	-448
Dividends paid to common stockholders	-7,036	0
Net cash provided by (used in) financing activities	26,105	-297,818
Net increase (decrease) in cash and cash equivalents	75,704	-302,789
Cash and cash equivalents at beginning of period	534,827	801,332
Cash and cash equivalents at end of period	610,531	498,543
Supplemental disclosures of cash flow information:	'	'
Cash paid during the period for income taxes	0	3,376
Cash paid during the period for interest expense	$4,561	$5,859

Basis_of_Presentation

Basis of Presentation	3 Months Ended
	Mar. 31, 2014
Organization, Consolidation and Presentation of Financial Statements [Abstract]	'
Basis of Presentation	'
	Basis of Presentation
	In the opinion of management, the accompanying unaudited consolidated financial statements of First Interstate BancSystem, Inc. and subsidiaries (the “Company”) contain all adjustments (all of which are of a normal recurring nature) necessary to present fairly the financial position of the Company at March 31, 2014 and December 31, 2013, and the results of operations and cash flows for each of the three month periods ended March 31, 2014 and 2013 in conformity with U.S. generally accepted accounting principles. The balance sheet information at December 31, 2013 is derived from audited consolidated financial statements. Certain reclassifications, none of which were material, have been made to conform prior year financial statements to the March 31, 2014 presentation. These reclassifications did not change previously reported net income or stockholders’ equity.
	These unaudited consolidated financial statements should be read in conjunction with the audited consolidated financial statements and related notes included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2013. Operating results for the three months ended March 31, 2014 are not necessarily indicative of the results that may be expected for the year ending December 31, 2014.

Investment_Securities

Investment Securities	3 Months Ended
	Mar. 31, 2014
Investments, Debt and Equity Securities [Abstract]	'
Investment Securities	'
	Investment Securities
	The amortized cost and approximate fair values of investment securities are summarized as follows:
	March 31, 2014	Amortized		Gross			Gross			Estimated
		Cost		Unrealized			Unrealized			Fair
				Gains			Losses			Value
	Available-for-Sale:
	Obligations of U.S. government agencies	$	712,895	$	1,563		$	(7,866	)	$	706,592
	U.S. agency residential mortgage-backed securities & collateralized mortgage obligations	1,190,134		13,316			(16,779		)	1,186,671
	Private mortgage-backed securities	384		7			(2		)	389
	Total	$	1,903,413	$	14,886		$	(24,647	)	$	1,893,652
	March 31, 2014	Amortized		Gross			Gross			Estimated
		Cost		Unrealized			Unrealized			Fair
				Gains			Losses			Value
	Held-to-Maturity:
	State, county and municipal securities	$	183,472	$	5,101		$	(1,209	)	$	187,364
	Corporate securities	17,964		115			—			18,079
	Total	$	201,436	$	5,216		$	(1,209	)	$	205,443
	December 31, 2013	Amortized		Gross			Gross			Estimated
		Cost		Unrealized			Unrealized			Fair
				Gains			Losses			Value
	Available-for-Sale:
	Obligations of U.S. government agencies	$	774,055	$	1,432		$	(12,249	)	$	763,238
	U.S. agency residential mortgage-backed securities & collateralized mortgage obligations	1,197,295		11,905			(25,147		)	1,184,053
	Private mortgage-backed securities	407		9			(1		)	415
	Total	$	1,971,757	$	13,346		$	(37,397	)	$	1,947,706
	December 31, 2013	Amortized		Gross			Gross			Estimated
		Cost		Unrealized			Unrealized			Fair
				Gains			Losses			Value
	Held-to-Maturity:
	State, county and municipal securities	$	185,818	$	4,043		$	(2,049	)	$	187,812
	Corporate securities	18,019		103			(8		)	18,114
	Total	$	203,837	$	4,146		$	(2,057	)	$	205,926
	Gross realized gains and losses from the disposition of investment securities are summarized in the following table:
		Three Months Ended March 31,
		2014			2013
	Gross realized gains	$	225		$	8
	Gross realized losses	154			—
	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 March 31, 2014 and December 31, 2013
		Less than 12 Months						12 Months or More						Total
	March 31, 2014	Fair		Gross				Fair			Gross			Fair		Gross
		Value		Unrealized				Value			Unrealized			Value		Unrealized
				Losses							Losses					Losses
	Available-for-Sale:
	Obligations of U.S. government agencies	$	289,936	$	(4,862	)		$	143,933		$	(3,004	)	$	433,869	$	(7,866	)
	U.S. agency residential mortgage-backed securities & collateralized mortgage obligations	427,631		(6,268		)		304,999			(10,511		)	732,630		(16,779		)
	Private mortgage-backed securities	—		—				100			(2		)	100		(2		)
	Total	$	717,567	$	(11,130	)		$	449,032		$	(13,517	)	$	1,166,599	$	(24,647	)
		Less than 12 Months						12 Months or More						Total
	March 31, 2014	Fair		Gross				Fair			Gross			Fair		Gross
		Value		Unrealized				Value			Unrealized			Value		Unrealized
				Losses							Losses					Losses
	Held-to-Maturity:
	State, county and municipal securities	$	21,088	$	(473	)		$	21,777		$	(736	)	$	42,865	$	(1,209	)
	Total	$	21,088	$	(473	)		$	21,777		$	(736	)	$	42,865	$	(1,209	)
		Less than 12 Months						12 Months or More						Total
	December 31, 2013	Fair		Gross				Fair			Gross			Fair		Gross
		Value		Unrealized				Value			Unrealized			Value		Unrealized
				Losses							Losses					Losses
	Available-for-Sale:
	Obligations of U.S. government agencies	$	458,385	$	(10,355	)		$	59,362		$	(1,894	)	$	517,747	$	(12,249	)
	U.S. agency residential mortgage-backed securities & collateralized mortgage obligations	634,199		(17,273		)		166,930			(7,874		)	801,129		(25,147		)
	Private mortgage-backed securities	—		—				104			(1		)	104		(1		)
	Total	$	1,092,584	$	(27,628	)		$	226,396		$	(9,769	)	$	1,318,980	$	(37,397	)
	Less than 12 Months						12 Months or More						Total
December 31, 2013	Fair		Gross				Fair			Gross			Fair		Gross
	Value		Unrealized				Value			Unrealized			Value		Unrealized
			Losses							Losses					Losses
Held-to-Maturity:
State, county and municipal securities	$	37,550	$	(1,319	)		$	14,296		$	(730	)	$	51,846	$	(2,049	)
Corporate securities	7,294		(8		)		—			—			7,294		(8		)
Total	$	44,844	$	(1,327	)		$	14,296		$	(730	)	$	59,140	$	(2,057	)
The investment portfolio is evaluated quarterly for other-than-temporary declines in the market value of each individual investment security. The Company had 198 and 229 individual investment securities that were in an unrealized loss position as of March 31, 2014 and December 31, 2013, respectively. Unrealized losses as of March 31, 2014 and December 31, 2013 related primarily to fluctuations in the current interest rates. The Company does not have the intent to sell any of the available-for-sale securities in the above table and it is not likely that the Company will have to sell any such securities before a recovery in cost. No impairment losses were recorded during the three months ended March 31, 2014 and 2013.
Maturities of investment securities at March 31, 2014 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
March 31, 2014	Amortized		Estimated				Amortized			Estimated
	Cost		Fair Value				Cost			Fair Value
Within one year	$	249,676	$	249,281			$	6,992		$	7,067
After one year but within five years	1,200,266		1,195,368				59,141			59,905
After five years but within ten years	393,945		389,650				84,471			86,512
After ten years	59,526		59,353				50,832			51,959
Total	$	1,903,413	$	1,893,652			$	201,436		$	205,443
As of March 31, 2014, the Company had investment securities callable within one year with amortized costs and estimated fair values of $200,270 and $198,596, respectively, including callable structured notes with amortized costs and estimated fair values of $54,985 and $54,994, 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.

Loans

Loans	3 Months Ended
	Mar. 31, 2014
Receivables [Abstract]	'
Loans	'
	Loans
	The following table presents loans by class as of the dates indicated:
		March 31,			December 31,
		2014			2013
	Real estate loans:
	Commercial	$	1,452,967		$	1,449,174
	Construction:
	Land acquisition & development	197,582			205,911
	Residential	81,411			76,488
	Commercial	75,356			69,236
	Total construction loans	354,349			351,635
	Residential	868,836			867,912
	Agricultural	160,570			173,534
	Total real estate loans	2,836,722			2,842,255
	Consumer:
	Indirect consumer	481,482			476,012
	Other consumer	130,614			133,039
	Credit card	58,310			62,536
	Total consumer loans	670,406			671,587
	Commercial	707,237			676,544
	Agricultural	108,376			111,872
	Other, including overdrafts	3,626			1,734
	Loans held for investment	4,326,367			4,303,992
	Mortgage loans held for sale	38,471			40,861
	Total loans	$	4,364,838		$	4,344,853
	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 dates indicated:
										Total Loans
		30 - 59		60 - 89			> 90			30 or More
		Days		Days			Days			Days		Current		Non-accrual		Total
	As of March 31, 2014	Past Due		Past Due			Past Due			Past Due		Loans		Loans		Loans
	Real estate
	Commercial	$	12,692	$	142		$	231		$	13,065	$	1,395,474	$	44,428	$	1,452,967
	Construction:
	Land acquisition & development	249		—			38			287		184,664		12,631		197,582
	Residential	403		—			—			403		79,932		1,076		81,411
	Commercial	8,389		—			—			8,389		66,747		220		75,356
	Total construction loans	9,041		—			38			9,079		331,343		13,927		354,349
	Residential	2,722		449			628			3,799		858,698		6,339		868,836
	Agricultural	2,221		4,903			—			7,124		144,692		8,754		160,570
	Total real estate loans	26,676		5,494			897			33,067		2,730,207		73,448		2,836,722
	Consumer:
	Indirect consumer	2,193		302			10			2,505		478,631		346		481,482
	Other consumer	758		73			25			856		129,182		576		130,614
	Credit card	183		244			363			790		57,502		18		58,310
	Total consumer loans	3,134		619			398			4,151		665,315		940		670,406
	Commercial	3,544		679			303			4,526		689,319		13,392		707,237
	Agricultural	770		118			103			991		107,051		334		108,376
	Other, including overdrafts	—		—			—			—		3,626		—		3,626
	Loans held for investment	34,124		6,910			1,701			42,735		4,195,518		88,114		4,326,367
	Mortgage loans originated for sale	—		—			—			—		38,471		—		38,471
	Total loans	$	34,124	$	6,910		$	1,701		$	42,735	$	4,233,989	$	88,114	$	4,364,838
										Total Loans
		30 - 59		60 - 89			> 90			30 or More
		Days		Days			Days			Days		Current		Non-accrual		Total
	As of December 31, 2013	Past Due		Past Due			Past Due			Past Due		Loans		Loans		Loans
	Real estate
	Commercial	$	5,924	$	2,472		$	22		$	8,418	$	1,391,823	$	48,933	$	1,449,174
	Construction:
	Land acquisition & development	1,062		468			38			1,568		188,074		16,269		205,911
	Residential	933		250			—			1,183		73,933		1,372		76,488
	Commercial	584		—			—			584		68,427		225		69,236
	Total construction loans	2,579		718			38			3,335		330,434		17,866		351,635
	Residential	3,630		206			1,162			4,998		856,800		6,114		867,912
Agricultural	328		646			—			974		163,986		8,574		173,534
Total real estate loans	12,461		4,042			1,222			17,725		2,743,043		81,487		2,842,255
Consumer:
Indirect consumer	3,303		430			9			3,742		471,906		364		476,012
Other consumer	925		130			1			1,056		131,508		475		133,039
Credit card	364		187			515			1,066		61,451		19		62,536
Total consumer loans	4,592		747			525			5,864		664,865		858		671,587
Commercial	2,791		1,186			563			4,540		660,035		11,969		676,544
Agricultural	453		672			—			1,125		110,622		125		111,872
Other, including overdrafts	—		—			—			—		1,734		—		1,734
Loans held for investment	20,297		6,647			2,310			29,254		4,180,299		94,439		4,303,992
Mortgage loans originated for sale	—		—			—			—		40,861		—		40,861
Total loans	$	20,297	$	6,647		$	2,310		$	29,254	$	4,221,160	$	94,439	$	4,344,853
If interest on non-accrual loans had been accrued, such income would have been approximately $1,121 and $1,352 for the three months ended March 31, 2014 and 2013.
The Company considers impaired loans to include all loans risk rated doubtful, loans placed on non-accrual status and loans renegotiated in troubled debt restructurings with the exception of consumer loans. The following tables present information on the Company’s recorded investment in impaired loans as of dates indicated:
As of March 31, 2014	Unpaid		Recorded			Recorded			Total		Related
	Total		Investment			Investment			Recorded		Allowance
	Principal		With No			With			Investment
	Balance		Allowance			Allowance
Real estate:
Commercial	$	58,383	$	29,901		$	26,701		$	56,602	$	4,617
Construction:
Land acquisition & development	17,776		8,679			4,642			13,321		597
Residential	1,519		1,076			—			1,076		—
Commercial	390		274			83			357		83
Total construction loans	19,685		10,029			4,725			14,754		680
Residential	9,894		5,536			901			6,437		380
Agricultural	9,075		6,663			2,316			8,979		275
Total real estate loans	97,037		52,129			34,643			86,772		5,952
Commercial	16,178		11,579			2,885			14,464		1,458
Agricultural	745		609			84			693		84
Total	$	113,960	$	64,317		$	37,612		$	101,929	$	7,494
As of December 31, 2013	Unpaid		Recorded			Recorded			Total		Related
	Total		Investment			Investment			Recorded		Allowance
	Principal		With No			With			Investment
	Balance		Allowance			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:
	Three Months Ended March 31,
	2014							2013
	Average Recorded Investment			Income Recognized				Average Recorded Investment			Income Recognized
Real estate:
Commercial	$	62,312		$	216			$	73,936		$	338
Construction:
Land acquisition & development	15,553			11				22,641			441
Residential	1,320			—				2,259			—
Commercial	360			2				7,898			—
Total construction loans	17,233			13				32,798			441
Residential	6,128			2				10,519			4
Agricultural	9,233			4				4,948			4
Total real estate loans	94,906			235				122,201			787
Commercial	14,268			14				12,746			18
Agricultural	288			6				632			4
Total	$	109,462		$	255			$	135,579		$	809
The amount of interest income recognized by the Company within the period that the loans were impaired was primarily related to loans modified in a troubled debt restructuring 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 would have been approximately $1,111 and $1,335 for the three months ended March 31, 2014 and 2013, respectively.
Collateralized impaired loans are generally recorded at the fair value of the underlying collateral 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 concessions, 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 are typically 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.
The Company had loans renegotiated in troubled debt restructurings of $58,320 as of March 31, 2014, of which $38,633 were included in non-accrual loans and $19,687 were on accrual status. The Company had loans renegotiated in troubled debt restructurings of $59,792 as of December 31, 2013, of which $38,011 were included in non-accrual loans and $21,781 were on accrual status.
The following tables present information on the Company's troubled debt restructurings that occurred during the three months ended March 31, 2014:
		Number of Notes	Type of Concession										Principal Balance at Restructure Date
Three Months Ended March 31, 2014			Interest only period			Extension of terms or maturity			Interest rate adjustment		Other (1)
Real estate:
Commercial		4	$	2,473		$	—		$	—	$	243	$	2,716
Total real estate loans		4	2,473			—			—		243		2,716
Commercial		2	226			—			—		30		256
Total loans restructured during period		6	$	2,699		$	—		$	—	$	273	$	2,972
(1) Other includes concessions that reduce or defer payments for a specified period of time and/or do not fit into other designated categories.
For troubled debt restructurings that were on non-accrual status or otherwise deemed impaired before the modification, a specific reserve may already be recorded. In periods subsequent to modification, the Company continues to evaluate all troubled debt restructurings for possible impairment and recognizes impairment through the allowance. Additionally these loans continue to work their way through the credit cycle through charge-off, pay-off or foreclosure. Financial effects of modifications of troubled debt restructurings may include principal loan forgiveness or other charge-offs directly related to the restructuring. The Company had no charge-offs directly related to modifying troubled debt restructurings during the three months ended March 31, 2014 or 2013.
The Company considers a payment default to occur on troubled debt restructurings when the loan is 90 days or more past due or was placed on non-accrual status after the modification. The Company had no troubled debt restructurings during the previous 12 months for which there was a payment default during the three months ended March 31, 2014.
At March 31, 2014, 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 loan 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 March 31, 2014	Other Assets		Substandard			Doubtful			Total
	Especially								Criticized
	Mentioned								Loans
Real estate:
Commercial	$	85,017	$	83,404		$	18,834		$	187,255
Construction:
Land acquisition & development	12,249		19,994			2,966			35,209
Residential	2,386		1,594			—			3,980
Commercial	272		461			82			815
Total construction loans	14,907		22,049			3,048			40,004
Residential	10,586		10,498			1,137			22,221
Agricultural	13,717		10,865			2,316			26,898
Total real estate loans	124,227		126,816			25,335			276,378
Consumer:
Indirect consumer	949		1,654			112			2,715
Other consumer	504		804			377			1,685
Credit card			239			1,671			1,910
Total consumer loans	1,453		2,697			2,160			6,310
Commercial	37,291		29,513			3,853			70,657
Agricultural	11,863		2,077			324			14,264
Total	$	174,834	$	161,103		$	31,672		$	367,609
As of December 31, 2013	Other Assets		Substandard			Doubtful			Total
	Especially								Criticized
	Mentioned								Loans
Real estate:
Commercial	$	79,747	$	86,426		$	24,840		$	191,013
Construction:
Land acquisition & development	13,211		19,677			7,329			40,217
Residential	1,859		1,649			277			3,785
Commercial	—		409			84			493
Total construction loans	15,070		21,735			7,690			44,495
Residential	7,500		7,188			4,184			18,872
Agricultural	13,597		10,245			2,370			26,212
Total real estate loans	115,914		125,594			39,084			280,592
Consumer:
Indirect consumer	875		1,524			115			2,514
Other consumer	573		969			268			1,810
Credit card	—		392			2,010			2,402
Total consumer loans	1,448		2,885			2,393			6,726
Commercial	33,318		23,833			3,745			60,896
Agricultural	8,401		1,788			86			10,275
Total	$	159,081	$	154,100		$	45,308		$	358,489
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	3 Months Ended
	Mar. 31, 2014
Receivables [Abstract]	'
Allowance For Loan Losses	'
	Allowance For Loan Losses
	The following tables present a summary of changes in the allowance for loan losses by portfolio segment for the periods indicated.
	Three Months Ended March 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 to operating expense	(3,375		)	(578		)	(1,072		)	25			—		(5,000		)
	Less loans charged-off	(1,085		)	(846		)	(796		)	(64		)	—		(2,791		)
	Add back recoveries of loans previously	367			608			2,822			26			—		3,823
	charged-off
	Ending balance	$	59,830		$	5,377		$	15,701		$	463		$	—	$	81,371
	Loans individually evaluated for impairment	$	5,952		$	—		$	1,458		$	84		$	—	$	7,494
	Loans collectively evaluated for impairment	53,878			5,377			14,243			379			—		73,877
	Allowance for loan losses	$	59,830		$	5,377		$	15,701		$	463		$	—	$	81,371
	Total loans:
	Individually evaluated for impairment	$	86,772		$	—		$	14,464		$	693		$	—	$	101,929
	Collectively evaluated for impairment	2,788,421			670,406			692,773			107,683			3,626		4,262,909
	Total loans	$	2,875,193		$	670,406		$	707,237		$	108,376		$	3,626	$	4,364,838
	Three Months Ended March 31, 2013	Real Estate			Consumer			Commercial			Agriculture			Other		Total
	Allowance for loan losses:
	Beginning balance	$	75,782		$	7,140		$	17,085		$	504		$	—	$	100,511
	Provision charged to operating expense	(1,035		)	537			1,021			(23		)	—		500
	Less loans charged-off	(4,143		)	(1,062		)	(811		)	(4		)	—		(6,020		)
	Add back recoveries of loans previously	1,062			473			1,375			3			—		2,913
	charged-off
	Ending balance	$	71,666		$	7,088		$	18,670		$	480		$	—	$	97,904
	Allowance for loan losses:
	Loans individually evaluated for impairment	$	8,367		$	—		$	3,725		$	25		$	—	$	12,117
	Loans collectively evaluated for impairment	63,299			7,088			14,945			455			—		85,787
	Allowance for loan losses	$	71,666		$	7,088		$	18,670		$	480		$	—	$	97,904
	Total loans:
	Individually evaluated for impairment	$	114,690		$	—		$	15,832		$	152		$	—	$	130,674
	Collectively evaluated for impairment	2,671,943			636,364			673,012			111,259			1,307		4,093,885
	Total loans	$	2,786,633		$	636,364		$	688,844		$	111,411		$	1,307	$	4,224,559
	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 economic 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 conditions and the estimated impact of these factors on historical loss rates.

OREO

OREO	3 Months Ended
	Mar. 31, 2014
Repossessed Assets [Abstract]	'
Other Real Estate Owned	'
	Other Real Estate Owned
	Information with respect to the Company's other real estate owned follows:
		Three Months Ended March 31,
		2014			2013
	Beginning balance	$	15,504		$	32,571
	Additions	3,415			5,331
	Capitalized improvements	—			10
	Valuation adjustments	—			(2,305		)
	Dispositions	(2,325		)	(3,137		)
	Ending balance	$	16,594		$	32,470

Capital_Stock

Capital Stock	3 Months Ended
	Mar. 31, 2014
Equity [Abstract]	'
Common Stock	'
	Capital Stock
	The Company had 20,343,161 shares of Class A common stock and 24,046,934 shares of Class B common stock outstanding as of March 31, 2014. The Company had 19,868,018 shares of Class A common stock and 24,287,045 shares of Class B common stock outstanding as of December 31, 2013.
	During February 2014, the Company repurchased and retired 100,355 of its shares of Class A common stock in a privately negotiated transaction at an aggregate purchase price of $2,538. The repurchase was made pursuant to a stock repurchase program approved by the Company's Board of Directors in November 2013. Under the terms of the stock repurchase program, the Company may repurchase up to an additional 1,899,645 shares of its Class A common stock prior to expiration of the plan on November 25, 2014. All other stock repurchases during the three months ended March 31, 2014 and 2013 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 January 24, 2014, the Company filed a Registration Statement on Form S-8 to register an additional 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.

Earnings_per_Common_Share

Earnings per Common Share	3 Months Ended
	Mar. 31, 2014
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 share for the three month periods ended March 31, 2014 and 2013.
		Three Months Ended March 31,
		2014		2013
	Net income	$	21,393	$	20,044
	Weighted average common shares outstanding for basic earnings per share computation	43,997,815		43,140,409
	Dilutive effects of stock-based compensation	622,961		287,973
	Weighted average common shares outstanding for diluted earnings per common share computation	44,620,776		43,428,382
	Basic earnings per common share	$	0.49	$	0.46
	Diluted earnings per common share	$	0.48	$	0.46
	The Company had 111,417 and 61,760 shares of unvested restricted stock as of March 31, 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. In addition, the Company had 1,025,419 stock options outstanding as of March 31, 2013, that were not included in the computation of diluted earnings per common share because their effect would be anti-dilutive.

Regulatory_Capital

Regulatory Capital	3 Months Ended
	Mar. 31, 2014
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. 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. 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 March 31, 2014 and December 31, 2013, the Company exceeded all capital adequacy requirements to which it is subject.
	Actual capital amounts and ratios and selected minimum regulatory thresholds for the Company and its bank subsidiary, First Interstate Bank (“FIB”), as of March 31, 2014 and December 31, 2013 are presented in the following tables:
		Actual				Adequately Capitalized				Well Capitalized
		Amount		Ratio		Amount		Ratio		Amount		Ratio
	March 31, 2014
	Total risk-based capital:
	Consolidated	$	836,502	16.8	%	$	397,506	8	%	NA		NA
	FIB	728,681		14.7		395,309		8		$	494,136	10	%
	Tier 1 risk-based capital:
	Consolidated	753,154		15.2		198,753		4		NA		NA
	FIB	657,672		13.3		197,654		4		$	296,482	6
	Leverage capital ratio:
	Consolidated	753,154		10.3		293,212		4		NA		NA
	FIB	657,672		9		291,961		4		$	364,952	5
		Actual				Adequately Capitalized				Well Capitalized
		Amount		Ratio		Amount		Ratio		Amount		Ratio
	December 31, 2013
	Total risk-based capital:
	Consolidated	$	829,443	16.8	%	$	396,210	8	%	NA		NA
	FIB	723,955		14.7		394,038		8		$	492,548	10	%
	Tier 1 risk-based capital:
	Consolidated	739,246		14.9		198,105		4		NA		NA
	FIB	650,093		13.2		197,019		4		$	295,529	6
	Leverage capital ratio:
	Consolidated	739,246		10.1		293,414		4		NA		NA
	FIB	650,093		8.9		292,199		4		$	365,248	5

Commitments_and_Contingencies

Commitments and Contingencies	3 Months Ended
	Mar. 31, 2014
Commitments and Contingencies Disclosure [Abstract]	'
Commitments and Contingencies	'
	Commitments and Contingencies
	In the normal course of business, the Company is involved in various 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 agreements of $1,050 as of March 31, 2014.

Financial_Instruments_with_Off

Financial Instruments with Off-Balance Sheet Risk	3 Months Ended
	Mar. 31, 2014
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. 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. Since many of the commitments are expected to expire without being drawn upon, the total commitment amounts do not necessarily represent future cash requirements. At March 31, 2014, commitments to extend credit to existing and new borrowers approximated $1,259,320 which included $413,564 on unused credit card lines and $306,519 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. At March 31, 2014, the Company had outstanding standby letters of credit of $59,909. The estimated fair value of the obligation undertaken by the Company in issuing the standby letters of credit is included in other liabilities in the Company’s consolidated balance sheet.

Supplemental_Disclosures_to_Co

Supplemental Disclosures to Consolidated Statement of Cash Flows	3 Months Ended
	Mar. 31, 2014
Supplemental Cash Flow Information [Abstract]	'
Supplemental Disclosures to Consolidated Statement of Cash Flows	'
	Supplemental Disclosures to Consolidated Statement of Cash Flows
	The Company transferred loans of $3,415 and $5,331 to OREO during the three months ended March 31, 2014 and 2013, respectively.
	The Company transferred internally originated mortgage servicing rights of $483 and $1,144 from loans to mortgage servicing assets during the three months ended March 31, 2014 and 2013, respectively.
	The Company reclassified tax credit investments with a carrying value of $429 from held-to-maturity investment securities to other assets during the three months ended March 31, 2013.

Other_Comprehensive_Income

Other Comprehensive Income	3 Months Ended
	Mar. 31, 2014
Equity [Abstract]	'
Other Comprehensive Income	'
	Other Comprehensive Income/Loss
	The gross amounts of each component of other comprehensive income (loss) and the related tax effects are as follows:
		Pre-tax						Tax Expense (Benefit)						Net of Tax
	Three Months Ended March 31,	2014			2013			2014			2013			2014			2013
	Investment securities available-for sale:
	Change in net unrealized gains/losses	$	14,351		$	(5,717	)	$	5,647		$	(2,250	)	$	8,704		$	(3,467	)
	during period
	Reclassification adjustment for net gains	(71		)	(8		)	(28		)	(3		)	(43		)	(5		)
	included in net income
	Defined benefits post-retirement benefit plan:
	Change in net actuarial loss	35			35			14			14			21			21
	Total other comprehensive income (loss)	$	14,315		$	(5,690	)	$	5,633		$	(2,239	)	$	8,682		$	(3,451	)
	The components of accumulated other comprehensive loss, net of income tax benefits, are as follows:
		March 31,			December 31,
		2014			2013
	Net unrealized loss on investment securities available-for-sale	$	(5,917	)	$	(14,578	)
	Net actuarial loss on defined benefit post-retirement benefit plans	(1,442		)	(1,463		)
	Net accumulated other comprehensive loss	$	(7,359	)	$	(16,041	)

Fair_Value_Measurements

Fair Value Measurements	3 Months Ended
	Mar. 31, 2014
Fair Value Disclosures [Abstract]	'
Fair Value Measurements	'
	Fair Value Measurements
	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 March 31, 2014	Balance		Quoted Prices in		Significant Other		Significant
				Active Markets for		Observable		Unobservable
				Identical Assets		Inputs		Inputs
				(Level 1)		(Level 2)		(Level 3)
	Investment securities available-for-sale:
	Obligations of U.S. government agencies	$	706,592	$	—	$	706,592	$	—
	U.S. agencies mortgage-backed securities & collateralized mortgage obligations	1,186,671		—		1,186,671		—
	Private mortgage-backed securities	389		—		389		—
	Mortgage servicing rights	26,215		—		26,215		—
				Fair Value Measurements at Reporting Date Using
	As of December 31, 2013	Balance		Quoted Prices in		Significant Other		Significant
				Active Markets for		Observable		Unobservable
				Identical Assets		Inputs		Inputs
				(Level 1)		(Level 2)		(Level 3)
	Investment securities available-for-sale:
	Obligations of U.S. government agencies	$	763,238	$	—	$	763,238	$	—
	U.S. agencies mortgage-backed securities & collateralized mortgage obligations	1,184,053		—		1,184,053		—
	Private mortgage-backed securities	415		—		415		—
	Mortgage servicing rights	25,698		—		25,698		—
	There were no changes in valuation methodologies or transfers between levels of the fair value hierarchy during the three months ended March 31, 2014 or 2013.
	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. The Company obtains fair value measurements for investment securities from an independent pricing service and evaluates mortgage servicing rights for impairment using an independent valuation service. The 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. 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 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.
	Mortgage Servicing Rights. Mortgage servicing rights are initially recorded at fair value based on comparable market quotes and are amortized in proportion to and over the period of estimated net servicing income. Mortgage servicing rights are evaluated quarterly for impairment using an independent valuation service. The valuation service utilizes discounted cash flow modeling techniques, which consider observable data that includes market consensus prepayment speeds and the predominant risk characteristics of the underlying loans including loan type, note rate and loan term. Management believes the significant inputs utilized in the valuation model are observable in the market.
	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 March 31, 2014	Balance		Quoted Prices in		Significant Other		Significant
				Active Markets for		Observable		Unobservable
				Identical Assets		Inputs		Inputs
				(Level 1)		(Level 2)		(Level 3)
	Impaired loans	$	48,347	$	—	$	—	$	48,347
	Other real estate owned	7,748		—		—		7,748
	Long-lived assets to be disposed of by sale	1,186		—		—		1,186
				Fair Value Measurements at Reporting Date Using
	As of December 31, 2013	Balance		Quoted Prices in		Significant Other		Significant
				Active Markets for		Observable		Unobservable
				Identical Assets		Inputs		Inputs
				(Level 1)		(Level 2)		(Level 3)
	Impaired loans	$	57,302	$	—	$	—	$	57,302
	Other real estate owned	8,502		—		—		8,502
	Long-lived assets to be disposed of by sale	1,186		—		—		1,186
	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 March 31, 2014, certain impaired loans with a carrying value of $67,872 were reduced by specific valuation allowance allocations of $7,493 and partial loan charge-offs of $12,032 resulting in a reported fair value of $48,347. As of December 31, 2013, certain impaired loans with a carrying value of $80,526 were reduced by specific valuation allowance allocations of $8,929 and partial loan charge-offs of $14,295 resulting in a reported fair value of $57,302.
	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. Write-downs of $2,305 during the three months ended March 31, 2013, were based on management's estimate of the current fair value of properties. No write-downs were recorded during the three months ended March 31, 2014.
	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 March 31, 2014 and December 31, 2013, the Company had long-lived assets to be disposed of by sale with a carrying value of $1,785 that was reduced by write-downs of $599 resulting in a fair value of $1,186 .
	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 March 31, 2014 and December 31, 2013, all mortgage loans held for sale were recorded at cost.
	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 held-to-maturity 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 fixed and floating rate subordinated debentures, floating rate subordinated term loan, notes payable to the FHLB, fixed rate subordinated term debt, and capital lease obligation are estimated by discounting future cash flows using current rates for advances with similar characteristics.
	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.
	The estimated fair values of financial instruments that are reported in the Company's consolidated balance sheets, segregated by the level of the valuation inputs within the fair value hierarchy utilized to measure fair value, are as follows:
						Fair Value Measurements at Reporting Date Using
	As of March 31, 2014	Carrying Amount		Estimated		Quoted Prices in		Significant Other		Significant
				Fair Value		Active Markets for		Observable		Unobservable
						Identical Assets		Inputs		Inputs
						(Level 1)		(Level 2)		(Level 3)
	Financial assets:
	Cash and cash equivalents	$	610,531	$	610,531	$	—	$	610,531	$	—
	Investment securities available-for-sale	1,893,652		1,893,652		—		1,893,652		—
	Investment securities held-to-maturity	201,436		205,443		—		205,443		—
	Accrued interest receivable	27,135		27,135		—		27,135		—
Mortgage servicing rights, net	13,474		26,215		—		26,215		—
Net loans	4,283,467		4,272,639		—		4,224,292		48,347
Total financial assets	$	7,029,695	$	7,035,615	$	—	$	6,987,268	$	48,347
Financial liabilities:
Total deposits, excluding time deposits	$	4,975,781	$	4,975,781	$	—	$	4,975,781	$	—
Time deposits	1,159,356		1,166,103		—		1,166,103		—
Securities sold under repurchase agreements	488,898		488,898		—		488,898		—
Other borrowed funds	9		9		—		9		—
Accrued interest payable	4,953		4,953		—		4,953		—
Long-term debt	36,905		35,200		—		35,200		—
Subordinated debentures held by subsidiary	82,477		73,607		—		73,607		—
trusts
Total financial liabilities	$	6,748,379	$	6,744,551	$	—	$	6,744,551	$	—
					Fair Value Measurements at Reporting Date Using
As of December 31, 2013	Carrying Amount		Estimated		Quoted Prices in		Significant Other		Significant
			Fair Value		Active Markets for		Observable		Unobservable
					Identical Assets		Inputs		Inputs
					(Level 1)		(Level 2)		(Level 3)
Financial assets:
Cash and cash equivalents	$	534,827	$	534,827	$	—	$	534,827	$	—
Investment securities available-for-sale	1,947,706		1,947,706		—		1,947,706		—
Investment securities held-to-maturity	203,837		205,926		—		205,926		—
Accrued interest receivable	26,450		26,450		—		26,450		—
Mortgage servicing rights, net	13,546		25,698		—		25,698		—
Net loans	4,259,514		4,246,539		—		4,189,237		57,302
Total financial assets	$	6,985,880	$	6,987,146	$	—	$	6,929,844	$	57,302
Financial liabilities:
Total deposits, excluding time deposits	$	4,943,033	$	4,943,033	$	—	$	4,943,033	$	—
Time deposits	1,190,717		1,196,250		—		1,196,250		—
Securities sold under repurchase agreements	457,437		457,437		—		457,437		—
Other borrowed funds	3		3		—		3		—
Accrued interest payable	4,963		4,963		—		4,963		—
Long-term debt	36,917		34,508		—		34,508		—
Subordinated debentures held by subsidiary	82,477		72,045		—		72,045		—
trusts
Total financial liabilities	$	6,715,547	$	6,708,239	$	—	$	6,708,239	$	—

Acquisitions

Acquisitions	3 Months Ended
	Mar. 31, 2014
Business Combinations [Abstract]	'
Acquisitions	'
	Acquisitions
	On February 10, 2014, the Company entered into an agreement and plan of merger to acquire all of the outstanding stock of Mountain West Financial Corp ("Mountain West"), a Montana-based bank holding company that operates one wholly-owned subsidiary bank, Mountain West Bank, NA, with branches located in five of the Company's current market areas in Montana. As of December 31, 2013, Mountain West had loans of approximately $405,409 and deposits of approximately $539,920.
	Under the terms of the agreement and plan of merger, each outstanding share of Mountain West common stock will be canceled and converted into the right to receive 0.2552 shares of the Company's Class A common stock plus $7.125 in cash, or, if a Mountain West stockholder properly elects and subject to the limitations contained within the agreement and plan of merger, an amount in all cash or all stock intended to be substantially equal in value to the above described combination of stock and cash merger consideration. The value received by Mountain West stockholders in the aggregate and on a per share of Mountain West common stock basis will fluctuate prior to the completion of the merger based on the prevailing market price of the Company's Class A common stock at the time the transaction is consummated. Based on the closing price of the Company's Class A common stock on the NASDAQ Global Select Market on March 31, 2014 of $28.22 per share, and on the number of shares and options to purchase shares of Mountain West common stock issued and outstanding on March 31, 2014, the aggregate value of the consideration expected to be paid would be $78,814, of which $39,920 would be paid in cash and $38,894 would be represented by 1,378,230 shares of the Company's Class A common stock.
	The merger is expected to close in mid-2014, subject to several conditions, including, among other things, receipt of applicable regulatory approval and approval by the stockholders of Mountain West. The Company anticipates that within six months following the consummation of the merger, Mountain West Bank, NA will be merged with and into FIB.

Recent_Authoritative_Accountin

Recent Authoritative Accounting Guidance	3 Months Ended
	Mar. 31, 2014
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]	'
Recent Authoritative Accounting Guidance	'
	Recent Authoritative Accounting Guidance
	ASU 2014-01 “Investments-Equity Method and Joint Ventures (Topic 323): Accounting for Investments in Qualified Affordable Housing Projects.” The amendments in ASU 2014-01 permit reporting entities to make an accounting policy election to account for their investments in qualified affordable housing projects using the proportional amortization method if certain conditions are met. The evaluation of whether conditions have been met to apply the proportional amortization method is conducted at the time of initial investment and subsequently reevaluated if there is a change in the nature of the investment or a change in the relationship with the limited liability entity that could result in the conditions no longer being met. The decision to apply the proportional amortization method of accounting should be applied consistently to all qualifying affordable housing project investments rather than on an individual investment basis. Under the proportional amortization method, an entity amortizes the initial cost of the investment in proportion to the tax credits and other tax benefits received and recognizes the net investment performance in the income statement as a component of income tax expense or benefit. The amendments in ASU 2014-01 are effective for the Company for annual reporting periods and interim reporting periods within those annual periods, beginning after December 15, 2014, with early adoption permitted.
	The Company adopted the amendments in ASU 2014-01 effective January 1, 2014. As of March 31, 2014, the Company had two investments in qualified affordable housing projects with an aggregate carrying value of $3,062 included in other assets on the Company's balance sheet. The Company elected to account for these investments using the proportional amortization method. During the three months ended March 31, 2014, income tax benefits associated with these projects of $7 were recognized as a component of income tax expense. The Company has commitments to invest additional amounts in these projects of $1,434 in 2014, $4,101 in 2015, $25 annually in 2016 through 2021, and $15 annually in 2022 and 2023.
	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 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 foreclosures 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 amendments in ASU 2014-04 are effective for the Company for annual periods, and interim periods within those annual periods, beginning after December 15, 2014 using either a modified retrospective transition method or a prospective transition method. The Company does not expect the amendments in ASU 2014-04 to have a material impact on the Company’s consolidated financial statements, results of operations or liquidity.

Subsequent_Events

Subsequent Events	3 Months Ended
	Mar. 31, 2014
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 April 28, 2014, the Company declared a quarterly dividend to common shareholders of $0.16 per share, to be paid on May 19, 2014 to shareholders of record as of May 8, 2014. No other events requiring recognition or disclosure were identified.

Investment_Securities_Tables

Investment Securities (Tables)	3 Months Ended
	Mar. 31, 2014
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:
	March 31, 2014	Amortized		Gross			Gross			Estimated
		Cost		Unrealized			Unrealized			Fair
				Gains			Losses			Value
	Available-for-Sale:
	Obligations of U.S. government agencies	$	712,895	$	1,563		$	(7,866	)	$	706,592
	U.S. agency residential mortgage-backed securities & collateralized mortgage obligations	1,190,134		13,316			(16,779		)	1,186,671
	Private mortgage-backed securities	384		7			(2		)	389
	Total	$	1,903,413	$	14,886		$	(24,647	)	$	1,893,652
	March 31, 2014	Amortized		Gross			Gross			Estimated
		Cost		Unrealized			Unrealized			Fair
				Gains			Losses			Value
	Held-to-Maturity:
	State, county and municipal securities	$	183,472	$	5,101		$	(1,209	)	$	187,364
	Corporate securities	17,964		115			—			18,079
	Total	$	201,436	$	5,216		$	(1,209	)	$	205,443
	December 31, 2013	Amortized		Gross			Gross			Estimated
		Cost		Unrealized			Unrealized			Fair
				Gains			Losses			Value
	Available-for-Sale:
	Obligations of U.S. government agencies	$	774,055	$	1,432		$	(12,249	)	$	763,238
	U.S. agency residential mortgage-backed securities & collateralized mortgage obligations	1,197,295		11,905			(25,147		)	1,184,053
	Private mortgage-backed securities	407		9			(1		)	415
	Total	$	1,971,757	$	13,346		$	(37,397	)	$	1,947,706
	December 31, 2013	Amortized		Gross			Gross			Estimated
		Cost		Unrealized			Unrealized			Fair
				Gains			Losses			Value
	Held-to-Maturity:
	State, county and municipal securities	$	185,818	$	4,043		$	(2,049	)	$	187,812
	Corporate securities	18,019		103			(8		)	18,114
	Total	$	203,837	$	4,146		$	(2,057	)	$	205,926
Realized Gains (Losses) on Investments	'
	Gross realized gains and losses from the disposition of investment securities are summarized in the following table:
		Three Months Ended March 31,
		2014			2013
	Gross realized gains	$	225		$	8
	Gross realized losses	154			—
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 March 31, 2014 and December 31, 2013
		Less than 12 Months						12 Months or More						Total
	March 31, 2014	Fair		Gross				Fair			Gross			Fair		Gross
		Value		Unrealized				Value			Unrealized			Value		Unrealized
				Losses							Losses					Losses
	Available-for-Sale:
	Obligations of U.S. government agencies	$	289,936	$	(4,862	)		$	143,933		$	(3,004	)	$	433,869	$	(7,866	)
	U.S. agency residential mortgage-backed securities & collateralized mortgage obligations	427,631		(6,268		)		304,999			(10,511		)	732,630		(16,779		)
	Private mortgage-backed securities	—		—				100			(2		)	100		(2		)
	Total	$	717,567	$	(11,130	)		$	449,032		$	(13,517	)	$	1,166,599	$	(24,647	)
		Less than 12 Months						12 Months or More						Total
	March 31, 2014	Fair		Gross				Fair			Gross			Fair		Gross
		Value		Unrealized				Value			Unrealized			Value		Unrealized
				Losses							Losses					Losses
	Held-to-Maturity:
	State, county and municipal securities	$	21,088	$	(473	)		$	21,777		$	(736	)	$	42,865	$	(1,209	)
	Total	$	21,088	$	(473	)		$	21,777		$	(736	)	$	42,865	$	(1,209	)
		Less than 12 Months						12 Months or More						Total
	December 31, 2013	Fair		Gross				Fair			Gross			Fair		Gross
		Value		Unrealized				Value			Unrealized			Value		Unrealized
				Losses							Losses					Losses
	Available-for-Sale:
	Obligations of U.S. government agencies	$	458,385	$	(10,355	)		$	59,362		$	(1,894	)	$	517,747	$	(12,249	)
	U.S. agency residential mortgage-backed securities & collateralized mortgage obligations	634,199		(17,273		)		166,930			(7,874		)	801,129		(25,147		)
	Private mortgage-backed securities	—		—				104			(1		)	104		(1		)
	Total	$	1,092,584	$	(27,628	)		$	226,396		$	(9,769	)	$	1,318,980	$	(37,397	)
		Less than 12 Months						12 Months or More						Total
	December 31, 2013	Fair		Gross				Fair			Gross			Fair		Gross
		Value		Unrealized				Value			Unrealized			Value		Unrealized
				Losses							Losses					Losses
	Held-to-Maturity:
	State, county and municipal securities	$	37,550	$	(1,319	)		$	14,296		$	(730	)	$	51,846	$	(2,049	)
	Corporate securities	7,294		(8		)		—			—			7,294		(8		)
	Total	$	44,844	$	(1,327	)		$	14,296		$	(730	)	$	59,140	$	(2,057	)
Maturities of Investment Securities	'
	Maturities of investment securities at March 31, 2014 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
	March 31, 2014	Amortized		Estimated				Amortized			Estimated
		Cost		Fair Value				Cost			Fair Value
	Within one year	$	249,676	$	249,281			$	6,992		$	7,067
	After one year but within five years	1,200,266		1,195,368				59,141			59,905
	After five years but within ten years	393,945		389,650				84,471			86,512
	After ten years	59,526		59,353				50,832			51,959
	Total	$	1,903,413	$	1,893,652			$	201,436		$	205,443

Loans_Tables

Loans (Tables)	3 Months Ended
	Mar. 31, 2014
Receivables [Abstract]	'
Schedule of Loans by Class	'
	The following table presents loans by class as of the dates indicated:
		March 31,			December 31,
		2014			2013
	Real estate loans:
	Commercial	$	1,452,967		$	1,449,174
	Construction:
	Land acquisition & development	197,582			205,911
	Residential	81,411			76,488
	Commercial	75,356			69,236
	Total construction loans	354,349			351,635
	Residential	868,836			867,912
	Agricultural	160,570			173,534
	Total real estate loans	2,836,722			2,842,255
	Consumer:
	Indirect consumer	481,482			476,012
	Other consumer	130,614			133,039
	Credit card	58,310			62,536
	Total consumer loans	670,406			671,587
	Commercial	707,237			676,544
	Agricultural	108,376			111,872
	Other, including overdrafts	3,626			1,734
	Loans held for investment	4,326,367			4,303,992
	Mortgage loans held for sale	38,471			40,861
	Total loans	$	4,364,838		$	4,344,853
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 dates indicated:
										Total Loans
		30 - 59		60 - 89			> 90			30 or More
		Days		Days			Days			Days		Current		Non-accrual		Total
	As of March 31, 2014	Past Due		Past Due			Past Due			Past Due		Loans		Loans		Loans
	Real estate
	Commercial	$	12,692	$	142		$	231		$	13,065	$	1,395,474	$	44,428	$	1,452,967
	Construction:
	Land acquisition & development	249		—			38			287		184,664		12,631		197,582
	Residential	403		—			—			403		79,932		1,076		81,411
	Commercial	8,389		—			—			8,389		66,747		220		75,356
	Total construction loans	9,041		—			38			9,079		331,343		13,927		354,349
	Residential	2,722		449			628			3,799		858,698		6,339		868,836
	Agricultural	2,221		4,903			—			7,124		144,692		8,754		160,570
	Total real estate loans	26,676		5,494			897			33,067		2,730,207		73,448		2,836,722
	Consumer:
	Indirect consumer	2,193		302			10			2,505		478,631		346		481,482
	Other consumer	758		73			25			856		129,182		576		130,614
	Credit card	183		244			363			790		57,502		18		58,310
	Total consumer loans	3,134		619			398			4,151		665,315		940		670,406
	Commercial	3,544		679			303			4,526		689,319		13,392		707,237
	Agricultural	770		118			103			991		107,051		334		108,376
	Other, including overdrafts	—		—			—			—		3,626		—		3,626
	Loans held for investment	34,124		6,910			1,701			42,735		4,195,518		88,114		4,326,367
	Mortgage loans originated for sale	—		—			—			—		38,471		—		38,471
	Total loans	$	34,124	$	6,910		$	1,701		$	42,735	$	4,233,989	$	88,114	$	4,364,838
										Total Loans
		30 - 59		60 - 89			> 90			30 or More
		Days		Days			Days			Days		Current		Non-accrual		Total
	As of December 31, 2013	Past Due		Past Due			Past Due			Past Due		Loans		Loans		Loans
	Real estate
	Commercial	$	5,924	$	2,472		$	22		$	8,418	$	1,391,823	$	48,933	$	1,449,174
	Construction:
	Land acquisition & development	1,062		468			38			1,568		188,074		16,269		205,911
	Residential	933		250			—			1,183		73,933		1,372		76,488
	Commercial	584		—			—			584		68,427		225		69,236
	Total construction loans	2,579		718			38			3,335		330,434		17,866		351,635
	Residential	3,630		206			1,162			4,998		856,800		6,114		867,912
	Agricultural	328		646			—			974		163,986		8,574		173,534
	Total real estate loans	12,461		4,042			1,222			17,725		2,743,043		81,487		2,842,255
	Consumer:
	Indirect consumer	3,303		430			9			3,742		471,906		364		476,012
	Other consumer	925		130			1			1,056		131,508		475		133,039
	Credit card	364		187			515			1,066		61,451		19		62,536
	Total consumer loans	4,592		747			525			5,864		664,865		858		671,587
	Commercial	2,791		1,186			563			4,540		660,035		11,969		676,544
	Agricultural	453		672			—			1,125		110,622		125		111,872
	Other, including overdrafts	—		—			—			—		1,734		—		1,734
	Loans held for investment	20,297		6,647			2,310			29,254		4,180,299		94,439		4,303,992
	Mortgage loans originated for sale	—		—			—			—		40,861		—		40,861
	Total loans	$	20,297	$	6,647		$	2,310		$	29,254	$	4,221,160	$	94,439	$	4,344,853
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:
	As of March 31, 2014	Unpaid		Recorded			Recorded			Total		Related
		Total		Investment			Investment			Recorded		Allowance
		Principal		With No			With			Investment
		Balance		Allowance			Allowance
	Real estate:
	Commercial	$	58,383	$	29,901		$	26,701		$	56,602	$	4,617
	Construction:
	Land acquisition & development	17,776		8,679			4,642			13,321		597
	Residential	1,519		1,076			—			1,076		—
	Commercial	390		274			83			357		83
	Total construction loans	19,685		10,029			4,725			14,754		680
	Residential	9,894		5,536			901			6,437		380
	Agricultural	9,075		6,663			2,316			8,979		275
	Total real estate loans	97,037		52,129			34,643			86,772		5,952
	Commercial	16,178		11,579			2,885			14,464		1,458
	Agricultural	745		609			84			693		84
	Total	$	113,960	$	64,317		$	37,612		$	101,929	$	7,494
	As of December 31, 2013	Unpaid		Recorded			Recorded			Total		Related
		Total		Investment			Investment			Recorded		Allowance
		Principal		With No			With			Investment
		Balance		Allowance			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:
		Three Months Ended March 31,
		2014							2013
		Average Recorded Investment			Income Recognized				Average Recorded Investment			Income Recognized
	Real estate:
	Commercial	$	62,312		$	216			$	73,936		$	338
	Construction:
	Land acquisition & development	15,553			11				22,641			441
	Residential	1,320			—				2,259			—
	Commercial	360			2				7,898			—
	Total construction loans	17,233			13				32,798			441
	Residential	6,128			2				10,519			4
	Agricultural	9,233			4				4,948			4
	Total real estate loans	94,906			235				122,201			787
	Commercial	14,268			14				12,746			18
	Agricultural	288			6				632			4
	Total	$	109,462		$	255			$	135,579		$	809
Schedule of Loans Renegotiated in Troubled Debt Restructurings	'
	The Company considers a payment default to occur on troubled debt restructurings when the loan is 90 days or more past due or was placed on non-accrual status after the modification. The Company had no troubled debt restructurings during the previous 12 months for which there was a payment default during the three months ended March 31, 2014.
	The following tables present information on the Company's troubled debt restructurings that occurred during the three months ended March 31, 2014:
			Number of Notes	Type of Concession										Principal Balance at Restructure Date
	Three Months Ended March 31, 2014			Interest only period			Extension of terms or maturity			Interest rate adjustment		Other (1)
	Real estate:
	Commercial		4	$	2,473		$	—		$	—	$	243	$	2,716
	Total real estate loans		4	2,473			—			—		243		2,716
	Commercial		2	226			—			—		30		256
	Total loans restructured during period		6	$	2,699		$	—		$	—	$	273	$	2,972
	(1) Other includes concessions that reduce or defer payments for a specified period of time and/or do not fit into other designated categories.
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 March 31, 2014	Other Assets		Substandard			Doubtful			Total
		Especially								Criticized
		Mentioned								Loans
	Real estate:
	Commercial	$	85,017	$	83,404		$	18,834		$	187,255
	Construction:
	Land acquisition & development	12,249		19,994			2,966			35,209
	Residential	2,386		1,594			—			3,980
	Commercial	272		461			82			815
	Total construction loans	14,907		22,049			3,048			40,004
	Residential	10,586		10,498			1,137			22,221
	Agricultural	13,717		10,865			2,316			26,898
	Total real estate loans	124,227		126,816			25,335			276,378
	Consumer:
	Indirect consumer	949		1,654			112			2,715
	Other consumer	504		804			377			1,685
	Credit card			239			1,671			1,910
	Total consumer loans	1,453		2,697			2,160			6,310
	Commercial	37,291		29,513			3,853			70,657
	Agricultural	11,863		2,077			324			14,264
	Total	$	174,834	$	161,103		$	31,672		$	367,609
	As of December 31, 2013	Other Assets		Substandard			Doubtful			Total
		Especially								Criticized
		Mentioned								Loans
	Real estate:
	Commercial	$	79,747	$	86,426		$	24,840		$	191,013
	Construction:
	Land acquisition & development	13,211		19,677			7,329			40,217
	Residential	1,859		1,649			277			3,785
	Commercial	—		409			84			493
	Total construction loans	15,070		21,735			7,690			44,495
	Residential	7,500		7,188			4,184			18,872
	Agricultural	13,597		10,245			2,370			26,212
	Total real estate loans	115,914		125,594			39,084			280,592
	Consumer:
	Indirect consumer	875		1,524			115			2,514
	Other consumer	573		969			268			1,810
	Credit card	—		392			2,010			2,402
	Total consumer loans	1,448		2,885			2,393			6,726
	Commercial	33,318		23,833			3,745			60,896
	Agricultural	8,401		1,788			86			10,275
	Total	$	159,081	$	154,100		$	45,308		$	358,489

Allowance_for_Loan_Losses_Tabl

Allowance for Loan Losses (Tables)	3 Months Ended
	Mar. 31, 2014
Receivables [Abstract]	'
Schedule of Allowance for Loan Losses by Portfolio Segment	'
	The following tables present a summary of changes in the allowance for loan losses by portfolio segment for the periods indicated.
	Three Months Ended March 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 to operating expense	(3,375		)	(578		)	(1,072		)	25			—		(5,000		)
	Less loans charged-off	(1,085		)	(846		)	(796		)	(64		)	—		(2,791		)
	Add back recoveries of loans previously	367			608			2,822			26			—		3,823
	charged-off
	Ending balance	$	59,830		$	5,377		$	15,701		$	463		$	—	$	81,371
	Loans individually evaluated for impairment	$	5,952		$	—		$	1,458		$	84		$	—	$	7,494
	Loans collectively evaluated for impairment	53,878			5,377			14,243			379			—		73,877
	Allowance for loan losses	$	59,830		$	5,377		$	15,701		$	463		$	—	$	81,371
	Total loans:
	Individually evaluated for impairment	$	86,772		$	—		$	14,464		$	693		$	—	$	101,929
	Collectively evaluated for impairment	2,788,421			670,406			692,773			107,683			3,626		4,262,909
	Total loans	$	2,875,193		$	670,406		$	707,237		$	108,376		$	3,626	$	4,364,838
	Three Months Ended March 31, 2013	Real Estate			Consumer			Commercial			Agriculture			Other		Total
	Allowance for loan losses:
	Beginning balance	$	75,782		$	7,140		$	17,085		$	504		$	—	$	100,511
	Provision charged to operating expense	(1,035		)	537			1,021			(23		)	—		500
	Less loans charged-off	(4,143		)	(1,062		)	(811		)	(4		)	—		(6,020		)
	Add back recoveries of loans previously	1,062			473			1,375			3			—		2,913
	charged-off
	Ending balance	$	71,666		$	7,088		$	18,670		$	480		$	—	$	97,904
	Allowance for loan losses:
	Loans individually evaluated for impairment	$	8,367		$	—		$	3,725		$	25		$	—	$	12,117
	Loans collectively evaluated for impairment	63,299			7,088			14,945			455			—		85,787
	Allowance for loan losses	$	71,666		$	7,088		$	18,670		$	480		$	—	$	97,904
	Total loans:
	Individually evaluated for impairment	$	114,690		$	—		$	15,832		$	152		$	—	$	130,674
	Collectively evaluated for impairment	2,671,943			636,364			673,012			111,259			1,307		4,093,885
	Total loans	$	2,786,633		$	636,364		$	688,844		$	111,411		$	1,307	$	4,224,559

OREO_Tables

OREO (Tables)	3 Months Ended
	Mar. 31, 2014
Repossessed Assets [Abstract]	'
Other Real Estate Owned Roll Forward	'
	Information with respect to the Company's other real estate owned follows:
		Three Months Ended March 31,
		2014			2013
	Beginning balance	$	15,504		$	32,571
	Additions	3,415			5,331
	Capitalized improvements	—			10
	Valuation adjustments	—			(2,305		)
	Dispositions	(2,325		)	(3,137		)
	Ending balance	$	16,594		$	32,470

Earnings_per_Share_Tables

Earnings per Share (Tables)	3 Months Ended
	Mar. 31, 2014
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 share for the three month periods ended March 31, 2014 and 2013.
		Three Months Ended March 31,
		2014		2013
	Net income	$	21,393	$	20,044
	Weighted average common shares outstanding for basic earnings per share computation	43,997,815		43,140,409
	Dilutive effects of stock-based compensation	622,961		287,973
	Weighted average common shares outstanding for diluted earnings per common share computation	44,620,776		43,428,382
	Basic earnings per common share	$	0.49	$	0.46
	Diluted earnings per common share	$	0.48	$	0.46

Regulatory_Capital_Tables

Regulatory Capital (Tables)	3 Months Ended
	Mar. 31, 2014
Banking and Thrift [Abstract]	'
Schedule of Compliance with Regulatory Capital Requirements under Banking Regulations	'
	Actual capital amounts and ratios and selected minimum regulatory thresholds for the Company and its bank subsidiary, First Interstate Bank (“FIB”), as of March 31, 2014 and December 31, 2013 are presented in the following tables:
		Actual				Adequately Capitalized				Well Capitalized
		Amount		Ratio		Amount		Ratio		Amount		Ratio
	March 31, 2014
	Total risk-based capital:
	Consolidated	$	836,502	16.8	%	$	397,506	8	%	NA		NA
	FIB	728,681		14.7		395,309		8		$	494,136	10	%
	Tier 1 risk-based capital:
	Consolidated	753,154		15.2		198,753		4		NA		NA
	FIB	657,672		13.3		197,654		4		$	296,482	6
	Leverage capital ratio:
	Consolidated	753,154		10.3		293,212		4		NA		NA
	FIB	657,672		9		291,961		4		$	364,952	5
		Actual				Adequately Capitalized				Well Capitalized
		Amount		Ratio		Amount		Ratio		Amount		Ratio
	December 31, 2013
	Total risk-based capital:
	Consolidated	$	829,443	16.8	%	$	396,210	8	%	NA		NA
	FIB	723,955		14.7		394,038		8		$	492,548	10	%
	Tier 1 risk-based capital:
	Consolidated	739,246		14.9		198,105		4		NA		NA
	FIB	650,093		13.2		197,019		4		$	295,529	6
	Leverage capital ratio:
	Consolidated	739,246		10.1		293,414		4		NA		NA
	FIB	650,093		8.9		292,199		4		$	365,248	5

Other_Comprehensive_Income_Tab

Other Comprehensive Income (Tables)	3 Months Ended
	Mar. 31, 2014
Equity [Abstract]	'
Schedule of Comprehensive Income (Loss)	'
	Other Comprehensive Income/Loss
	The gross amounts of each component of other comprehensive income (loss) and the related tax effects are as follows:
		Pre-tax						Tax Expense (Benefit)						Net of Tax
	Three Months Ended March 31,	2014			2013			2014			2013			2014			2013
	Investment securities available-for sale:
	Change in net unrealized gains/losses	$	14,351		$	(5,717	)	$	5,647		$	(2,250	)	$	8,704		$	(3,467	)
	during period
	Reclassification adjustment for net gains	(71		)	(8		)	(28		)	(3		)	(43		)	(5		)
	included in net income
	Defined benefits post-retirement benefit plan:
	Change in net actuarial loss	35			35			14			14			21			21
	Total other comprehensive income (loss)	$	14,315		$	(5,690	)	$	5,633		$	(2,239	)	$	8,682		$	(3,451	)
Schedule of Accumulated Other Comprehensive Income (Loss)	'
	The components of accumulated other comprehensive loss, net of income tax benefits, are as follows:
		March 31,			December 31,
		2014			2013
	Net unrealized loss on investment securities available-for-sale	$	(5,917	)	$	(14,578	)
	Net actuarial loss on defined benefit post-retirement benefit plans	(1,442		)	(1,463		)
	Net accumulated other comprehensive loss	$	(7,359	)	$	(16,041	)

Fair_Value_Measurements_Tables

Fair Value Measurements (Tables)	3 Months Ended
	Mar. 31, 2014
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 March 31, 2014	Balance		Quoted Prices in		Significant Other		Significant
				Active Markets for		Observable		Unobservable
				Identical Assets		Inputs		Inputs
				(Level 1)		(Level 2)		(Level 3)
	Investment securities available-for-sale:
	Obligations of U.S. government agencies	$	706,592	$	—	$	706,592	$	—
	U.S. agencies mortgage-backed securities & collateralized mortgage obligations	1,186,671		—		1,186,671		—
	Private mortgage-backed securities	389		—		389		—
	Mortgage servicing rights	26,215		—		26,215		—
				Fair Value Measurements at Reporting Date Using
	As of December 31, 2013	Balance		Quoted Prices in		Significant Other		Significant
				Active Markets for		Observable		Unobservable
				Identical Assets		Inputs		Inputs
				(Level 1)		(Level 2)		(Level 3)
	Investment securities available-for-sale:
	Obligations of U.S. government agencies	$	763,238	$	—	$	763,238	$	—
	U.S. agencies mortgage-backed securities & collateralized mortgage obligations	1,184,053		—		1,184,053		—
	Private mortgage-backed securities	415		—		415		—
	Mortgage servicing rights	25,698		—		25,698		—
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 March 31, 2014	Balance		Quoted Prices in		Significant Other		Significant
				Active Markets for		Observable		Unobservable
				Identical Assets		Inputs		Inputs
				(Level 1)		(Level 2)		(Level 3)
	Impaired loans	$	48,347	$	—	$	—	$	48,347
	Other real estate owned	7,748		—		—		7,748
	Long-lived assets to be disposed of by sale	1,186		—		—		1,186
				Fair Value Measurements at Reporting Date Using
	As of December 31, 2013	Balance		Quoted Prices in		Significant Other		Significant
				Active Markets for		Observable		Unobservable
				Identical Assets		Inputs		Inputs
				(Level 1)		(Level 2)		(Level 3)
	Impaired loans	$	57,302	$	—	$	—	$	57,302
	Other real estate owned	8,502		—		—		8,502
	Long-lived assets to be disposed of by sale	1,186		—		—		1,186
Schedule of Estimated Fair Values of Financial Instruments by Level of Valuation Inputs	'
	The estimated fair values of financial instruments that are reported in the Company's consolidated balance sheets, segregated by the level of the valuation inputs within the fair value hierarchy utilized to measure fair value, are as follows:
						Fair Value Measurements at Reporting Date Using
	As of March 31, 2014	Carrying Amount		Estimated		Quoted Prices in		Significant Other		Significant
				Fair Value		Active Markets for		Observable		Unobservable
						Identical Assets		Inputs		Inputs
						(Level 1)		(Level 2)		(Level 3)
	Financial assets:
	Cash and cash equivalents	$	610,531	$	610,531	$	—	$	610,531	$	—
	Investment securities available-for-sale	1,893,652		1,893,652		—		1,893,652		—
	Investment securities held-to-maturity	201,436		205,443		—		205,443		—
	Accrued interest receivable	27,135		27,135		—		27,135		—
	Mortgage servicing rights, net	13,474		26,215		—		26,215		—
	Net loans	4,283,467		4,272,639		—		4,224,292		48,347
	Total financial assets	$	7,029,695	$	7,035,615	$	—	$	6,987,268	$	48,347
	Financial liabilities:
	Total deposits, excluding time deposits	$	4,975,781	$	4,975,781	$	—	$	4,975,781	$	—
	Time deposits	1,159,356		1,166,103		—		1,166,103		—
	Securities sold under repurchase agreements	488,898		488,898		—		488,898		—
	Other borrowed funds	9		9		—		9		—
	Accrued interest payable	4,953		4,953		—		4,953		—
	Long-term debt	36,905		35,200		—		35,200		—
	Subordinated debentures held by subsidiary	82,477		73,607		—		73,607		—
	trusts
	Total financial liabilities	$	6,748,379	$	6,744,551	$	—	$	6,744,551	$	—
						Fair Value Measurements at Reporting Date Using
	As of December 31, 2013	Carrying Amount		Estimated		Quoted Prices in		Significant Other		Significant
				Fair Value		Active Markets for		Observable		Unobservable
						Identical Assets		Inputs		Inputs
						(Level 1)		(Level 2)		(Level 3)
	Financial assets:
	Cash and cash equivalents	$	534,827	$	534,827	$	—	$	534,827	$	—
	Investment securities available-for-sale	1,947,706		1,947,706		—		1,947,706		—
	Investment securities held-to-maturity	203,837		205,926		—		205,926		—
	Accrued interest receivable	26,450		26,450		—		26,450		—
	Mortgage servicing rights, net	13,546		25,698		—		25,698		—
	Net loans	4,259,514		4,246,539		—		4,189,237		57,302
	Total financial assets	$	6,985,880	$	6,987,146	$	—	$	6,929,844	$	57,302
	Financial liabilities:
	Total deposits, excluding time deposits	$	4,943,033	$	4,943,033	$	—	$	4,943,033	$	—
	Time deposits	1,190,717		1,196,250		—		1,196,250		—
	Securities sold under repurchase agreements	457,437		457,437		—		457,437		—
	Other borrowed funds	3		3		—		3		—
	Accrued interest payable	4,963		4,963		—		4,963		—
	Long-term debt	36,917		34,508		—		34,508		—
	Subordinated debentures held by subsidiary	82,477		72,045		—		72,045		—
	trusts
	Total financial liabilities	$	6,715,547	$	6,708,239	$	—	$	6,708,239	$	—

Amortized_Cost_and_Approximate

Amortized Cost and Approximate Fair Values of Investment Securities (Details) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013
Schedule of Available for Sale and Held-to-Maturity Securities [Line Items]	'	'	'
Available-for-Sale Securities, Gross Realized Gains	$225	$8	'
Available-for-sale Securities, Gross Realized Losses	154	0	'
Available-for-Sale:	'	'	'
Available-for-Sale, Amortized Cost	1,903,413	'	1,971,757
Available-for-sale Securities, Gross Unrealized Gain1	14,886	'	13,346
Available-for-sale Securities, Gross Unrealized Loss1	-24,647	'	-37,397
Available-for-Sale, Estimated Fair Value	1,893,652	'	1,947,706
Held-to-Maturity:	'	'	'
Held-to-Maturity, Amortized Cost	201,436	'	203,837
Held-to-maturity Securities, Gross Unrealized Gain1	5,216	'	4,146
Held-to-maturity Securities, Gross Unrealized Loss1	-1,209	'	-2,057
Held-to-Maturity, Estimated Fair Value	205,443	'	205,926
Obligations of U.S. government agencies	'	'	'
Available-for-Sale:	'	'	'
Available-for-Sale, Amortized Cost	712,895	'	774,055
Available-for-sale Securities, Gross Unrealized Gain1	1,563	'	1,432
Available-for-sale Securities, Gross Unrealized Loss1	-7,866	'	-12,249
Available-for-Sale, Estimated Fair Value	706,592	'	763,238
U.S. agency residential mortgage-backed securities & collateralized mortgage obligations	'	'	'
Available-for-Sale:	'	'	'
Available-for-Sale, Amortized Cost	1,190,134	'	1,197,295
Available-for-sale Securities, Gross Unrealized Gain1	13,316	'	11,905
Available-for-sale Securities, Gross Unrealized Loss1	-16,779	'	-25,147
Available-for-Sale, Estimated Fair Value	1,186,671	'	1,184,053
Private mortgage-backed securities	'	'	'
Available-for-Sale:	'	'	'
Available-for-Sale, Amortized Cost	384	'	407
Available-for-sale Securities, Gross Unrealized Gain1	7	'	9
Available-for-sale Securities, Gross Unrealized Loss1	-2	'	-1
Available-for-Sale, Estimated Fair Value	389	'	415
State, county and municipal securities	'	'	'
Held-to-Maturity:	'	'	'
Held-to-Maturity, Amortized Cost	183,472	'	185,818
Held-to-maturity Securities, Gross Unrealized Gain1	5,101	'	4,043
Held-to-maturity Securities, Gross Unrealized Loss1	-1,209	'	-2,049
Held-to-Maturity, Estimated Fair Value	187,364	'	187,812
Corporate securities	'	'	'
Held-to-Maturity:	'	'	'
Held-to-Maturity, Amortized Cost	17,964	'	18,019
Held-to-maturity Securities, Gross Unrealized Gain1	115	'	103
Held-to-maturity Securities, Gross Unrealized Loss1	0	'	-8
Held-to-Maturity, Estimated Fair Value	$18,079	'	$18,114

Investment_Securities_Realized

Investment Securities Realized Gains (Losses) on Investments (Details) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Investments, Debt and Equity Securities [Abstract]	'	'
Gross realized gains	$225	$8
Gross realized losses	$154	$0

Investment_Securities_Gross_Un

Investment Securities Gross Unrealized Losses and Fair Values of Investment Securities (Details) (USD $)	Mar. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified	securities	securities
Available-for-Sale:	'	'
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	$717,567	$1,092,584
Available-for-sale Securities, Continuous Unrealized Loss Position, Less Than 12 months, Aggregate Loss1	-11,130	-27,628
Available-for-Sale, 12 Months or More Fair Value	449,032	226,396
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 months or Longer, Aggregate Loss1	-13,517	-9,769
Available-for-Sale, Total Fair Value	1,166,599	1,318,980
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss1	-24,647	-37,397
Held-to-Maturity:	'	'
Held-to-Maturity, Less than 12 Months Fair Value	21,088	44,844
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less Than 12 months, Aggregate Loss1	-473	-1,327
Held-to-Maturity, 12 Months or More Fair Value	21,777	14,296
Held-to-Maturity, 12 Months or More Gross Unrealized Losses	-736	-730
Held-to-Maturity, Total Fair Value	42,865	59,140
Held-to-maturity Securities, Continuous Unrealized Loss Position, Aggregate Loss1	-1,209	-2,057
Available-for-Sale and Held-to-Maturity:	'	'
Investment Securities in an Unrealized Loss Position (Number of Securities)	198	229
Obligations of U.S. government agencies	'	'
Available-for-Sale:	'	'
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	289,936	458,385
Available-for-sale Securities, Continuous Unrealized Loss Position, Less Than 12 months, Aggregate Loss1	-4,862	-10,355
Available-for-Sale, 12 Months or More Fair Value	143,933	59,362
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 months or Longer, Aggregate Loss1	-3,004	-1,894
Available-for-Sale, Total Fair Value	433,869	517,747
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss1	-7,866	-12,249
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	427,631	634,199
Available-for-sale Securities, Continuous Unrealized Loss Position, Less Than 12 months, Aggregate Loss1	-6,268	-17,273
Available-for-Sale, 12 Months or More Fair Value	304,999	166,930
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 months or Longer, Aggregate Loss1	-10,511	-7,874
Available-for-Sale, Total Fair Value	732,630	801,129
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss1	-16,779	-25,147
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, Aggregate Loss1	0	0
Available-for-Sale, 12 Months or More Fair Value	100	104
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 months or Longer, Aggregate Loss1	-2	-1
Available-for-Sale, Total Fair Value	100	104
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss1	-2	-1
State, county and municipal securities	'	'
Held-to-Maturity:	'	'
Held-to-Maturity, Less than 12 Months Fair Value	21,088	37,550
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less Than 12 months, Aggregate Loss1	-473	-1,319
Held-to-Maturity, 12 Months or More Fair Value	21,777	14,296
Held-to-Maturity, 12 Months or More Gross Unrealized Losses	-736	-730
Held-to-Maturity, Total Fair Value	42,865	51,846
Held-to-maturity Securities, Continuous Unrealized Loss Position, Aggregate Loss1	-1,209	-2,049
Corporate Debt Securities [Member]	'	'
Held-to-Maturity:	'	'
Held-to-Maturity, Less than 12 Months Fair Value	'	7,294
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less Than 12 months, Aggregate Loss1	'	-8
Held-to-Maturity, 12 Months or More Fair Value	'	0
Held-to-Maturity, 12 Months or More Gross Unrealized Losses	'	0
Held-to-Maturity, Total Fair Value	'	7,294
Held-to-maturity Securities, Continuous Unrealized Loss Position, Aggregate Loss1	'	($8)

Maturities_of_Investment_Secur

Maturities of Investment Securities (Details) (USD $)	Mar. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Rolling Maturity	'	'
Available-for-Sale Amortized Cost, Within One Year	$249,676	'
Available-for-Sale Amortized Cost, After One Year but Within Five Years	1,200,266	'
Available-for-Sale Amortized Cost, After Five Years but Within Ten Years	393,945	'
Available-for-Sale Amortized Cost, After Ten Years	59,526	'
Available-for-Sale Amortized Cost, Total	1,903,413	'
Available-for-sale Securities, Debt Maturities, Fair Value, Rolling Maturity	'	'
Available-for-Sale Estimated Fair Value, Within One Year	249,281	'
Available-for-Sale Estimated Fair Value, After One Year but Within Five Years	1,195,368	'
Available-for-Sale Estimated Fair Value, After Ten Years	389,650	'
Available-for-Sale Estimated Fair Value, After Five Years but Within Ten Years	59,353	'
Available-for-Sale, Estimated Fair Value	1,893,652	1,947,706
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount	'	'
Held-to-Maturity Amortized Cost, Within One Year	6,992	'
Held-to-Maturity Amortized Cost, After One Year but Within Five Years	59,141	'
Held-to-Maturity Amortized Cost, After Five Years but Within Ten Years	84,471	'
Held-to-Maturity Amortized Cost, After Ten Years	50,832	'
Held-to-Maturity Amortized Cost, Total	201,436	203,837
Held-to-maturity Securities, Debt Maturities, Fair Value, Rolling Maturity	'	'
Held-to-Maturity Estimated Fair Value, Within One Year	7,067	'
Held-to-Maturity Estimated Fair Value, After One Year but Within Five Years	59,905	'
Held-to-Maturity Estimated Fair Value, After Five Years but Within Ten Years	86,512	'
Held-to-Maturity Estimated Fair Value, After Ten Years	51,959	'
Held-to-Maturity, Estimated Fair Value	205,443	205,926
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	200,270	'
Investment Securities Primarily Classified as Available-for-Sale, Fair Value, After One Year but Within Five Years	198,596	'
Callable Structured Notes	'	'
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	54,985	'
Investment Securities Primarily Classified as Available-for-Sale, Fair Value, After One Year but Within Five Years	$54,994	'

Schedule_of_Loans_by_Class_Det

Schedule of Loans by Class (Details) (USD $)	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2013
In Thousands, unless otherwise specified
Loans and Leases Receivable [Line Items]	'	'	'
Loans held for investment	$4,326,367	$4,303,992	'
Mortgage loans held for sale	38,471	40,861	'
Total loans	4,364,838	4,344,853	4,224,559
Commercial real estate	'	'	'
Loans and Leases Receivable [Line Items]	'	'	'
Loans held for investment	1,452,967	1,449,174	'
Land acquisition & development construction real estate	'	'	'
Loans and Leases Receivable [Line Items]	'	'	'
Loans held for investment	197,582	205,911	'
Residential construction real estate	'	'	'
Loans and Leases Receivable [Line Items]	'	'	'
Loans held for investment	81,411	76,488	'
Commercial construction real estate	'	'	'
Loans and Leases Receivable [Line Items]	'	'	'
Loans held for investment	75,356	69,236	'
Total construction loans	'	'	'
Loans and Leases Receivable [Line Items]	'	'	'
Loans held for investment	354,349	351,635	'
Residential real estate	'	'	'
Loans and Leases Receivable [Line Items]	'	'	'
Loans held for investment	868,836	867,912	'
Agricultural real estate	'	'	'
Loans and Leases Receivable [Line Items]	'	'	'
Loans held for investment	160,570	173,534	'
Total real estate loans	'	'	'
Loans and Leases Receivable [Line Items]	'	'	'
Loans held for investment	2,836,722	2,842,255	'
Indirect consumer	'	'	'
Loans and Leases Receivable [Line Items]	'	'	'
Loans held for investment	481,482	476,012	'
Other consumer	'	'	'
Loans and Leases Receivable [Line Items]	'	'	'
Loans held for investment	130,614	133,039	'
Credit card consumer	'	'	'
Loans and Leases Receivable [Line Items]	'	'	'
Loans held for investment	58,310	62,536	'
Total consumer loans	'	'	'
Loans and Leases Receivable [Line Items]	'	'	'
Loans held for investment	670,406	671,587	'
Commercial	'	'	'
Loans and Leases Receivable [Line Items]	'	'	'
Loans held for investment	707,237	676,544	'
Agricultural	'	'	'
Loans and Leases Receivable [Line Items]	'	'	'
Loans held for investment	108,376	111,872	'
Other, including overdrafts	'	'	'
Loans and Leases Receivable [Line Items]	'	'	'
Loans held for investment	$3,626	$1,734	'

Schedule_of_Recorded_Investmen

Schedule of Recorded Investment in Past Due Loans by Class (Details) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]	'	'	'
Loans held for investment	$4,326,367	'	$4,303,992
Mortgage loans held for sale	38,471	'	40,861
Total loans	4,364,838	4,224,559	4,344,853
Interest Income on Non-Accrual Loans if Accrued	1,121	1,352	'
Commercial real estate	'	'	'
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]	'	'	'
30 to 59 Days Past Due	12,692	'	5,924
60 to 89 Days Past Due	142	'	2,472
Greater than 90 Days Past Due	231	'	22
Total Loans 30 or More Days Past Due	13,065	'	8,418
Current Loans	1,395,474	'	1,391,823
Non-accrual Loans	44,428	'	48,933
Loans held for investment	1,452,967	'	1,449,174
Land acquisition & development construction real estate	'	'	'
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]	'	'	'
30 to 59 Days Past Due	249	'	1,062
60 to 89 Days Past Due	0	'	468
Greater than 90 Days Past Due	38	'	38
Total Loans 30 or More Days Past Due	287	'	1,568
Current Loans	184,664	'	188,074
Non-accrual Loans	12,631	'	16,269
Loans held for investment	197,582	'	205,911
Residential construction real estate	'	'	'
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]	'	'	'
30 to 59 Days Past Due	403	'	933
60 to 89 Days Past Due	0	'	250
Greater than 90 Days Past Due	0	'	0
Total Loans 30 or More Days Past Due	403	'	1,183
Current Loans	79,932	'	73,933
Non-accrual Loans	1,076	'	1,372
Loans held for investment	81,411	'	76,488
Commercial construction real estate	'	'	'
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]	'	'	'
30 to 59 Days Past Due	8,389	'	584
60 to 89 Days Past Due	0	'	0
Greater than 90 Days Past Due	0	'	0
Total Loans 30 or More Days Past Due	8,389	'	584
Current Loans	66,747	'	68,427
Non-accrual Loans	220	'	225
Loans held for investment	75,356	'	69,236
Total construction loans	'	'	'
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]	'	'	'
30 to 59 Days Past Due	9,041	'	2,579
60 to 89 Days Past Due	0	'	718
Greater than 90 Days Past Due	38	'	38
Total Loans 30 or More Days Past Due	9,079	'	3,335
Current Loans	331,343	'	330,434
Non-accrual Loans	13,927	'	17,866
Loans held for investment	354,349	'	351,635
Residential real estate	'	'	'
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]	'	'	'
30 to 59 Days Past Due	2,722	'	3,630
60 to 89 Days Past Due	449	'	206
Greater than 90 Days Past Due	628	'	1,162
Total Loans 30 or More Days Past Due	3,799	'	4,998
Current Loans	858,698	'	856,800
Non-accrual Loans	6,339	'	6,114
Loans held for investment	868,836	'	867,912
Agricultural real estate	'	'	'
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]	'	'	'
30 to 59 Days Past Due	2,221	'	328
60 to 89 Days Past Due	4,903	'	646
Greater than 90 Days Past Due	0	'	0
Total Loans 30 or More Days Past Due	7,124	'	974
Current Loans	144,692	'	163,986
Non-accrual Loans	8,754	'	8,574
Loans held for investment	160,570	'	173,534
Total real estate loans	'	'	'
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]	'	'	'
30 to 59 Days Past Due	26,676	'	12,461
60 to 89 Days Past Due	5,494	'	4,042
Greater than 90 Days Past Due	897	'	1,222
Total Loans 30 or More Days Past Due	33,067	'	17,725
Current Loans	2,730,207	'	2,743,043
Non-accrual Loans	73,448	'	81,487
Loans held for investment	2,836,722	'	2,842,255
Indirect consumer	'	'	'
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]	'	'	'
30 to 59 Days Past Due	2,193	'	3,303
60 to 89 Days Past Due	302	'	430
Greater than 90 Days Past Due	10	'	9
Total Loans 30 or More Days Past Due	2,505	'	3,742
Current Loans	478,631	'	471,906
Non-accrual Loans	346	'	364
Loans held for investment	481,482	'	476,012
Other consumer	'	'	'
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]	'	'	'
30 to 59 Days Past Due	758	'	925
60 to 89 Days Past Due	73	'	130
Greater than 90 Days Past Due	25	'	1
Total Loans 30 or More Days Past Due	856	'	1,056
Current Loans	129,182	'	131,508
Non-accrual Loans	576	'	475
Loans held for investment	130,614	'	133,039
Credit card consumer	'	'	'
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]	'	'	'
30 to 59 Days Past Due	183	'	364
60 to 89 Days Past Due	244	'	187
Greater than 90 Days Past Due	363	'	515
Total Loans 30 or More Days Past Due	790	'	1,066
Current Loans	57,502	'	61,451
Non-accrual Loans	18	'	19
Loans held for investment	58,310	'	62,536
Total consumer loans	'	'	'
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]	'	'	'
30 to 59 Days Past Due	3,134	'	4,592
60 to 89 Days Past Due	619	'	747
Greater than 90 Days Past Due	398	'	525
Total Loans 30 or More Days Past Due	4,151	'	5,864
Current Loans	665,315	'	664,865
Non-accrual Loans	940	'	858
Loans held for investment	670,406	'	671,587
Commercial	'	'	'
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]	'	'	'
30 to 59 Days Past Due	3,544	'	2,791
60 to 89 Days Past Due	679	'	1,186
Greater than 90 Days Past Due	303	'	563
Total Loans 30 or More Days Past Due	4,526	'	4,540
Current Loans	689,319	'	660,035
Non-accrual Loans	13,392	'	11,969
Loans held for investment	707,237	'	676,544
Agricultural	'	'	'
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]	'	'	'
30 to 59 Days Past Due	770	'	453
60 to 89 Days Past Due	118	'	672
Greater than 90 Days Past Due	103	'	0
Total Loans 30 or More Days Past Due	991	'	1,125
Current Loans	107,051	'	110,622
Non-accrual Loans	334	'	125
Loans held for investment	108,376	'	111,872
Other, including overdrafts	'	'	'
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]	'	'	'
30 to 59 Days Past Due	0	'	0
60 to 89 Days Past Due	0	'	0
Greater than 90 Days Past Due	0	'	0
Total Loans 30 or More Days Past Due	0	'	0
Current Loans	3,626	'	1,734
Non-accrual Loans	0	'	0
Loans held for investment	3,626	'	1,734
Loans held for investment	'	'	'
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]	'	'	'
30 to 59 Days Past Due	34,124	'	20,297
60 to 89 Days Past Due	6,910	'	6,647
Greater than 90 Days Past Due	1,701	'	2,310
Total Loans 30 or More Days Past Due	42,735	'	29,254
Current Loans	4,195,518	'	4,180,299
Non-accrual Loans	88,114	'	94,439
Loans held for investment	4,326,367	'	4,303,992
Mortgage loans originated for sale	'	'	'
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]	'	'	'
30 to 59 Days Past Due	0	'	0
60 to 89 Days Past Due	0	'	0
Greater than 90 Days Past Due	0	'	0
Total Loans 30 or More Days Past Due	0	'	0
Current Loans	38,471	'	40,861
Non-accrual Loans	0	'	0
Total loans	'	'	'
Loans and Leases Receivable Recorded Investment, Past Due [Line Items]	'	'	'
30 to 59 Days Past Due	34,124	'	20,297
60 to 89 Days Past Due	6,910	'	6,647
Greater than 90 Days Past Due	1,701	'	2,310
Total Loans 30 or More Days Past Due	42,735	'	29,254
Current Loans	4,233,989	'	4,221,160
Non-accrual Loans	88,114	'	94,439
Total loans	$4,364,838	'	$4,344,853

Loans_Schedule_of_Recorded_Inv

Loans Schedule of Recorded Investment in Impaired Loans (Details) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013
Impaired Financing Receivable, Unpaid Principal Balance	'	'	'
Unpaid Total Principal Balance	$113,960	'	$124,867
Recorded Investment With No Allowance	64,317	'	62,724
Recorded Investment With Allowance	37,612	'	47,848
Total Recorded Investment	101,929	'	110,572
Related Allowance	7,494	'	8,929
Impaired Financing Receivable, Average Recorded Investment and Cash Basis Method Interest Income	'	'	'
Average Recorded Investment	109,462	135,579	'
Income Recognized	255	809	'
Interest Income on Impaired Loans If Interest Had Been Accrued	1,111	1,335	'
Commercial real estate	'	'	'
Impaired Financing Receivable, Unpaid Principal Balance	'	'	'
Unpaid Total Principal Balance	58,383	'	64,780
Recorded Investment With No Allowance	29,901	'	29,216
Recorded Investment With Allowance	26,701	'	33,937
Total Recorded Investment	56,602	'	63,153
Related Allowance	4,617	'	5,210
Impaired Financing Receivable, Average Recorded Investment and Cash Basis Method Interest Income	'	'	'
Average Recorded Investment	62,312	73,936	'
Income Recognized	216	338	'
Land acquisition & development construction real estate	'	'	'
Impaired Financing Receivable, Unpaid Principal Balance	'	'	'
Unpaid Total Principal Balance	17,776	'	23,906
Recorded Investment With No Allowance	8,679	'	9,901
Recorded Investment With Allowance	4,642	'	7,226
Total Recorded Investment	13,321	'	17,127
Related Allowance	597	'	1,434
Impaired Financing Receivable, Average Recorded Investment and Cash Basis Method Interest Income	'	'	'
Average Recorded Investment	15,553	22,641	'
Income Recognized	11	441	'
Residential construction real estate	'	'	'
Impaired Financing Receivable, Unpaid Principal Balance	'	'	'
Unpaid Total Principal Balance	1,519	'	1,816
Recorded Investment With No Allowance	1,076	'	1,095
Recorded Investment With Allowance	0	'	277
Total Recorded Investment	1,076	'	1,372
Related Allowance	0	'	26
Impaired Financing Receivable, Average Recorded Investment and Cash Basis Method Interest Income	'	'	'
Average Recorded Investment	1,320	2,259	'
Income Recognized	0	0	'
Commercial construction real estate	'	'	'
Impaired Financing Receivable, Unpaid Principal Balance	'	'	'
Unpaid Total Principal Balance	390	'	397
Recorded Investment With No Allowance	274	'	279
Recorded Investment With Allowance	83	'	84
Total Recorded Investment	357	'	363
Related Allowance	83	'	85
Impaired Financing Receivable, Average Recorded Investment and Cash Basis Method Interest Income	'	'	'
Average Recorded Investment	360	7,898	'
Income Recognized	2	0	'
Total construction loans	'	'	'
Impaired Financing Receivable, Unpaid Principal Balance	'	'	'
Unpaid Total Principal Balance	19,685	'	26,119
Recorded Investment With No Allowance	10,029	'	11,275
Recorded Investment With Allowance	4,725	'	7,587
Total Recorded Investment	14,754	'	18,862
Related Allowance	680	'	1,545
Impaired Financing Receivable, Average Recorded Investment and Cash Basis Method Interest Income	'	'	'
Average Recorded Investment	17,233	32,798	'
Income Recognized	13	441	'
Residential real estate	'	'	'
Impaired Financing Receivable, Unpaid Principal Balance	'	'	'
Unpaid Total Principal Balance	9,894	'	9,448
Recorded Investment With No Allowance	5,536	'	5,081
Recorded Investment With Allowance	901	'	967
Total Recorded Investment	6,437	'	6,048
Related Allowance	380	'	249
Impaired Financing Receivable, Average Recorded Investment and Cash Basis Method Interest Income	'	'	'
Average Recorded Investment	6,128	10,519	'
Income Recognized	2	4	'
Agricultural real estate	'	'	'
Impaired Financing Receivable, Unpaid Principal Balance	'	'	'
Unpaid Total Principal Balance	9,075	'	8,895
Recorded Investment With No Allowance	6,663	'	6,429
Recorded Investment With Allowance	2,316	'	2,370
Total Recorded Investment	8,979	'	8,799
Related Allowance	275	'	335
Impaired Financing Receivable, Average Recorded Investment and Cash Basis Method Interest Income	'	'	'
Average Recorded Investment	9,233	4,948	'
Income Recognized	4	4	'
Total real estate loans	'	'	'
Impaired Financing Receivable, Unpaid Principal Balance	'	'	'
Unpaid Total Principal Balance	97,037	'	109,242
Recorded Investment With No Allowance	52,129	'	52,001
Recorded Investment With Allowance	34,643	'	44,861
Total Recorded Investment	86,772	'	96,862
Related Allowance	5,952	'	7,339
Impaired Financing Receivable, Average Recorded Investment and Cash Basis Method Interest Income	'	'	'
Average Recorded Investment	94,906	122,201	'
Income Recognized	235	787	'
Commercial	'	'	'
Impaired Financing Receivable, Unpaid Principal Balance	'	'	'
Unpaid Total Principal Balance	16,178	'	15,448
Recorded Investment With No Allowance	11,579	'	10,684
Recorded Investment With Allowance	2,885	'	2,901
Total Recorded Investment	14,464	'	13,585
Related Allowance	1,458	'	1,504
Impaired Financing Receivable, Average Recorded Investment and Cash Basis Method Interest Income	'	'	'
Average Recorded Investment	14,268	12,746	'
Income Recognized	14	18	'
Agricultural	'	'	'
Impaired Financing Receivable, Unpaid Principal Balance	'	'	'
Unpaid Total Principal Balance	745	'	177
Recorded Investment With No Allowance	609	'	39
Recorded Investment With Allowance	84	'	86
Total Recorded Investment	693	'	125
Related Allowance	84	'	86
Impaired Financing Receivable, Average Recorded Investment and Cash Basis Method Interest Income	'	'	'
Average Recorded Investment	288	632	'
Income Recognized	$6	$4	'

Schedule_of_Loans_Renegotiated

Schedule of Loans Renegotiated in Troubled Debt Restructurings (Details) (USD $)	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013
	notes
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]	'	'	'
Financing Receivable, Modifications, Subsequent Default, Number of Contracts	0	'	'
Financing Receivables, Impaired, Troubled Debt Restructuring, Write-down	$0	$0	'
Loans Renegotiated in Troubled Debt Restructurings	58,320,000	'	59,792,000
Loans Renegotiated in Troubled Debt Restructurings, Non-Accrual Loans	38,633,000	'	38,011,000
Loans Renegotiated in Troubled Debt Restructurings, Accrual Loans	19,687,000	'	21,781,000
Number of Notes	6	'	'
Principle Balance at Restructure Date	2,972,000	'	'
Financing Receivable, Modifications, Subsequent Default, Recorded Investment	0	'	'
Loans and Leases Receivable, Impaired, Commitment to Lend	0	'	'
Interest only period	'	'	'
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]	'	'	'
Principle Balance at Restructure Date	2,699,000	'	'
Extension of terms or maturity	'	'	'
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]	'	'	'
Principle Balance at Restructure Date	0	'	'
Interest rate adjustment	'	'	'
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]	'	'	'
Principle Balance at Restructure Date	0	'	'
Other	'	'	'
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]	'	'	'
Principle Balance at Restructure Date	273,000	'	'
Commercial real estate	'	'	'
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]	'	'	'
Number of Notes	4	'	'
Principle Balance at Restructure Date	2,716,000	'	'
Commercial real estate | Interest only period	'	'	'
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]	'	'	'
Principle Balance at Restructure Date	2,473,000	'	'
Commercial real estate | Extension of terms or maturity	'	'	'
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]	'	'	'
Principle Balance at Restructure Date	0	'	'
Commercial real estate | Interest rate adjustment	'	'	'
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]	'	'	'
Principle Balance at Restructure Date	0	'	'
Commercial real estate | Other	'	'	'
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]	'	'	'
Principle Balance at Restructure Date	243,000	'	'
Total real estate loans	'	'	'
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]	'	'	'
Number of Notes	4	'	'
Principle Balance at Restructure Date	2,716,000	'	'
Total real estate loans | Interest only period	'	'	'
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]	'	'	'
Principle Balance at Restructure Date	2,473,000	'	'
Total real estate loans | Extension of terms or maturity	'	'	'
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]	'	'	'
Principle Balance at Restructure Date	0	'	'
Total real estate loans | Interest rate adjustment	'	'	'
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]	'	'	'
Principle Balance at Restructure Date	0	'	'
Total real estate loans | Other	'	'	'
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]	'	'	'
Principle Balance at Restructure Date	243,000	'	'
Commercial	'	'	'
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]	'	'	'
Number of Notes	0	'	'
Principle Balance at Restructure Date	256,000	'	'
Commercial | Interest only period	'	'	'
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]	'	'	'
Principle Balance at Restructure Date	226,000	'	'
Commercial | Extension of terms or maturity	'	'	'
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]	'	'	'
Principle Balance at Restructure Date	0	'	'
Commercial | Interest rate adjustment	'	'	'
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]	'	'	'
Principle Balance at Restructure Date	0	'	'
Commercial | Other	'	'	'
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]	'	'	'
Principle Balance at Restructure Date	$30,000	'	'

Schedule_of_Recorded_Investmen1

Schedule of Recorded Investment in Criticized Loans by Class and Credit Quality Indicator (Details) (USD $)	Mar. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]	'	'
Loans held for investment	$4,326,367	$4,303,992
Commercial real estate	'	'
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]	'	'
Loans held for investment	1,452,967	1,449,174
Land acquisition & development construction real estate	'	'
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]	'	'
Loans held for investment	197,582	205,911
Residential construction real estate	'	'
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]	'	'
Loans held for investment	81,411	76,488
Commercial construction real estate	'	'
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]	'	'
Loans held for investment	75,356	69,236
Total construction loans	'	'
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]	'	'
Loans held for investment	354,349	351,635
Residential real estate	'	'
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]	'	'
Loans held for investment	868,836	867,912
Agricultural real estate	'	'
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]	'	'
Loans held for investment	160,570	173,534
Total real estate loans	'	'
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]	'	'
Loans held for investment	2,836,722	2,842,255
Indirect consumer	'	'
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]	'	'
Loans held for investment	481,482	476,012
Other consumer	'	'
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]	'	'
Loans held for investment	130,614	133,039
Credit card consumer	'	'
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]	'	'
Loans held for investment	58,310	62,536
Total consumer loans	'	'
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]	'	'
Loans held for investment	670,406	671,587
Commercial	'	'
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]	'	'
Loans held for investment	707,237	676,544
Agricultural	'	'
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]	'	'
Loans held for investment	108,376	111,872
Other Assets Especially Mentioned	'	'
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]	'	'
Loans held for investment	174,834	159,081
Other Assets Especially Mentioned | Commercial real estate	'	'
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]	'	'
Loans held for investment	85,017	79,747
Other Assets Especially Mentioned | Land acquisition & development construction real estate	'	'
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]	'	'
Loans held for investment	12,249	13,211
Other Assets Especially Mentioned | Residential construction real estate	'	'
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]	'	'
Loans held for investment	2,386	1,859
Other Assets Especially Mentioned | Commercial construction real estate	'	'
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]	'	'
Loans held for investment	272	0
Other Assets Especially Mentioned | Total construction loans	'	'
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]	'	'
Loans held for investment	14,907	15,070
Other Assets Especially Mentioned | Residential real estate	'	'
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]	'	'
Loans held for investment	10,586	7,500
Other Assets Especially Mentioned | Agricultural real estate	'	'
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]	'	'
Loans held for investment	13,717	13,597
Other Assets Especially Mentioned | Total real estate loans	'	'
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]	'	'
Loans held for investment	124,227	115,914
Other Assets Especially Mentioned | Indirect consumer	'	'
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]	'	'
Loans held for investment	949	875
Other Assets Especially Mentioned | Other consumer	'	'
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]	'	'
Loans held for investment	504	573
Other Assets Especially Mentioned | Credit card consumer	'	'
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]	'	'
Loans held for investment	'	0
Other Assets Especially Mentioned | Total consumer loans	'	'
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]	'	'
Loans held for investment	1,453	1,448
Other Assets Especially Mentioned | Commercial	'	'
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]	'	'
Loans held for investment	37,291	33,318
Other Assets Especially Mentioned | Agricultural	'	'
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]	'	'
Loans held for investment	11,863	8,401
Substandard	'	'
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]	'	'
Loans held for investment	161,103	154,100
Substandard | Commercial real estate	'	'
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]	'	'
Loans held for investment	83,404	86,426
Substandard | Land acquisition & development construction real estate	'	'
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]	'	'
Loans held for investment	19,994	19,677
Substandard | Residential construction real estate	'	'
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]	'	'
Loans held for investment	1,594	1,649
Substandard | Commercial construction real estate	'	'
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]	'	'
Loans held for investment	461	409
Substandard | Total construction loans	'	'
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]	'	'
Loans held for investment	22,049	21,735
Substandard | Residential real estate	'	'
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]	'	'
Loans held for investment	10,498	7,188
Substandard | Agricultural real estate	'	'
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]	'	'
Loans held for investment	10,865	10,245
Substandard | Total real estate loans	'	'
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]	'	'
Loans held for investment	126,816	125,594
Substandard | Indirect consumer	'	'
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]	'	'
Loans held for investment	1,654	1,524
Substandard | Other consumer	'	'
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]	'	'
Loans held for investment	804	969
Substandard | Credit card consumer	'	'
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]	'	'
Loans held for investment	239	392
Substandard | Total consumer loans	'	'
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]	'	'
Loans held for investment	2,697	2,885
Substandard | Commercial	'	'
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]	'	'
Loans held for investment	29,513	23,833
Substandard | Agricultural	'	'
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]	'	'
Loans held for investment	2,077	1,788
Doubtful	'	'
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]	'	'
Loans held for investment	31,672	45,308
Doubtful | Commercial real estate	'	'
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]	'	'
Loans held for investment	18,834	24,840
Doubtful | Land acquisition & development construction real estate	'	'
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]	'	'
Loans held for investment	2,966	7,329
Doubtful | Residential construction real estate	'	'
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]	'	'
Loans held for investment	0	277
Doubtful | Commercial construction real estate	'	'
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]	'	'
Loans held for investment	82	84
Doubtful | Total construction loans	'	'
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]	'	'
Loans held for investment	3,048	7,690
Doubtful | Residential real estate	'	'
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]	'	'
Loans held for investment	1,137	4,184
Doubtful | Agricultural real estate	'	'
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]	'	'
Loans held for investment	2,316	2,370
Doubtful | Total real estate loans	'	'
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]	'	'
Loans held for investment	25,335	39,084
Doubtful | Indirect consumer	'	'
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]	'	'
Loans held for investment	112	115
Doubtful | Other consumer	'	'
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]	'	'
Loans held for investment	377	268
Doubtful | Credit card consumer	'	'
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]	'	'
Loans held for investment	1,671	2,010
Doubtful | Total consumer loans	'	'
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]	'	'
Loans held for investment	2,160	2,393
Doubtful | Commercial	'	'
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]	'	'
Loans held for investment	3,853	3,745
Doubtful | Agricultural	'	'
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]	'	'
Loans held for investment	324	86
Total Criticized Loans	'	'
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]	'	'
Loans held for investment	367,609	358,489
Total Criticized Loans | Commercial real estate	'	'
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]	'	'
Loans held for investment	187,255	191,013
Total Criticized Loans | Land acquisition & development construction real estate	'	'
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]	'	'
Loans held for investment	35,209	40,217
Total Criticized Loans | Residential construction real estate	'	'
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]	'	'
Loans held for investment	3,980	3,785
Total Criticized Loans | Commercial construction real estate	'	'
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]	'	'
Loans held for investment	815	493
Total Criticized Loans | Total construction loans	'	'
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]	'	'
Loans held for investment	40,004	44,495
Total Criticized Loans | Residential real estate	'	'
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]	'	'
Loans held for investment	22,221	18,872
Total Criticized Loans | Agricultural real estate	'	'
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]	'	'
Loans held for investment	26,898	26,212
Total Criticized Loans | Total real estate loans	'	'
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]	'	'
Loans held for investment	276,378	280,592
Total Criticized Loans | Indirect consumer	'	'
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]	'	'
Loans held for investment	2,715	2,514
Total Criticized Loans | Other consumer	'	'
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]	'	'
Loans held for investment	1,685	1,810
Total Criticized Loans | Credit card consumer	'	'
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]	'	'
Loans held for investment	1,910	2,402
Total Criticized Loans | Total consumer loans	'	'
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]	'	'
Loans held for investment	6,310	6,726
Total Criticized Loans | Commercial	'	'
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]	'	'
Loans held for investment	70,657	60,896
Total Criticized Loans | Agricultural	'	'
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]	'	'
Loans held for investment	$14,264	$10,275

Schedule_of_Allowance_for_Loan

Schedule of Allowance for Loan Losses by Portfolio Segment (Details) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013
Allowance for Loan and Lease Losses [Roll Forward]	'	'	'
Beginning balance	$85,339	$100,511	'
Provision charged to operating expense	-5,000	500	'
Less loans charged-off	-2,791	-6,020	'
Add back recoveries of loans previously charged-off	3,823	2,913	'
Ending balance	81,371	97,904	'
Allowance for loan losses:	'	'	'
Loans individually evaluated for impairment	7,494	12,117	'
Loans collectively evaluated for impairment	73,877	85,787	'
Ending balance	81,371	97,904	'
Total loans:	'	'	'
Individually evaluated for impairment	101,929	130,674	'
Individually evaluated for impairment	4,262,909	4,093,885	'
Total loans	4,364,838	4,224,559	4,344,853
Real Estate	'	'	'
Allowance for Loan and Lease Losses [Roll Forward]	'	'	'
Beginning balance	63,923	75,782	'
Provision charged to operating expense	-3,375	-1,035	'
Less loans charged-off	-1,085	-4,143	'
Add back recoveries of loans previously charged-off	367	1,062	'
Ending balance	59,830	71,666	'
Allowance for loan losses:	'	'	'
Loans individually evaluated for impairment	5,952	8,367	'
Loans collectively evaluated for impairment	53,878	63,299	'
Ending balance	59,830	71,666	'
Total loans:	'	'	'
Individually evaluated for impairment	86,772	114,690	'
Individually evaluated for impairment	2,788,421	2,671,943	'
Total loans	2,875,193	2,786,633	'
Consumer	'	'	'
Allowance for Loan and Lease Losses [Roll Forward]	'	'	'
Beginning balance	6,193	7,140	'
Provision charged to operating expense	-578	537	'
Less loans charged-off	-846	-1,062	'
Add back recoveries of loans previously charged-off	608	473	'
Ending balance	5,377	7,088	'
Allowance for loan losses:	'	'	'
Loans individually evaluated for impairment	0	0	'
Loans collectively evaluated for impairment	5,377	7,088	'
Ending balance	5,377	7,088	'
Total loans:	'	'	'
Individually evaluated for impairment	0	0	'
Individually evaluated for impairment	670,406	636,364	'
Total loans	670,406	636,364	'
Commercial	'	'	'
Allowance for Loan and Lease Losses [Roll Forward]	'	'	'
Beginning balance	14,747	17,085	'
Provision charged to operating expense	-1,072	1,021	'
Less loans charged-off	-796	-811	'
Add back recoveries of loans previously charged-off	2,822	1,375	'
Ending balance	15,701	18,670	'
Allowance for loan losses:	'	'	'
Loans individually evaluated for impairment	1,458	3,725	'
Loans collectively evaluated for impairment	14,243	14,945	'
Ending balance	15,701	18,670	'
Total loans:	'	'	'
Individually evaluated for impairment	14,464	15,832	'
Individually evaluated for impairment	692,773	673,012	'
Total loans	707,237	688,844	'
Agriculture	'	'	'
Allowance for Loan and Lease Losses [Roll Forward]	'	'	'
Beginning balance	476	504	'
Provision charged to operating expense	25	-23	'
Less loans charged-off	-64	-4	'
Add back recoveries of loans previously charged-off	26	3	'
Ending balance	463	480	'
Allowance for loan losses:	'	'	'
Loans individually evaluated for impairment	84	25	'
Loans collectively evaluated for impairment	379	455	'
Ending balance	463	480	'
Total loans:	'	'	'
Individually evaluated for impairment	693	152	'
Individually evaluated for impairment	107,683	111,259	'
Total loans	108,376	111,411	'
Other	'	'	'
Allowance for Loan and Lease Losses [Roll Forward]	'	'	'
Beginning balance	0	0	'
Provision charged to operating expense	0	0	'
Less loans charged-off	0	0	'
Add back recoveries of loans previously charged-off	0	0	'
Ending balance	0	0	'
Allowance for loan losses:	'	'	'
Loans individually evaluated for impairment	0	0	'
Loans collectively evaluated for impairment	0	0	'
Ending balance	0	0	'
Total loans:	'	'	'
Individually evaluated for impairment	0	0	'
Individually evaluated for impairment	3,626	1,307	'
Total loans	$3,626	$1,307	'

OREO_Details

OREO (Details) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Real Estate Acquired Through Foreclosure [Roll Forward]	'	'
Beginning balance	$15,504	$32,571
Additions	3,415	5,331
Capitalized improvements	0	10
Valuation adjustments	0	-2,305
Dispositions	-2,325	-3,137
Ending balance	$16,594	$32,470

Capital_Stock_Details

Capital Stock (Details) (USD $)	3 Months Ended		1 Months Ended			0 Months Ended
In Thousands, except Share data, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013	Feb. 28, 2014	Mar. 31, 2014	Dec. 31, 2013	Jan. 24, 2014	Mar. 31, 2014	Mar. 31, 2014	Dec. 31, 2013
			Class A Common Stock	Class A Common Stock	Class A Common Stock	Class A Common Stock	Class A Common Stock	Class B Common Stock	Class B Common Stock
						2006 Equity Compensation Plan [Member]	Share Repurchase Program [Domain]
Class of Stock [Line Items]	'	'	'	'	'	'	'	'	'
Common Stock, Shares, Outstanding	'	'	'	20,343,161	19,868,018	'	'	24,046,934	24,287,045
Stock Repurchased and Retired During Period, Shares	'	'	100,355	'	'	'	'	'	'
Payments for Repurchase of Common Stock	$3,159	$448	$2,538	'	'	'	'	'	'
Stock Repurchase Program, Remaining Authorized Repurchase Amount	'	'	'	'	'	'	1,899,645	'	'
Share-based Compensation Arrangement by Share-based Payment Award, Number of Additional Shares Authorized	'	'	'	'	'	1,500,000	'	'	'

Computation_of_Basic_and_Dilut

Computation of Basic and Diluted Earnings per Share (Details) (USD $)	3 Months Ended
In Thousands, except Share data, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Net Income (Loss) Available to Common Stockholders, Basic	'	'
Net income	$21,393	$20,044
Weighted Average Number of Shares Outstanding, Basic and Diluted	'	'
Weighted average common shares outstanding for basic earnings per share computation	43,997,815	43,140,409
Dilutive effect of stock-based compensation	622,961	287,973
Weighted average common shares outstanding for diluted earnings per common share computation	44,620,776	43,428,382
Earnings Per Share, Basic and Diluted	'	'
Basic earnings per common share	$0.49	$0.46
Diluted earnings per common share	$0.48	$0.46
Stock Options	'	'
Earnings Per Share, Basic and Diluted [Line Items]	'	'
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	'	1,025,419
Unvested Restricted Stock	'	'
Earnings Per Share, Basic and Diluted [Line Items]	'	'
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	111,417	61,760

Schedule_of_Actual_Capital_Amo

Schedule of Actual Capital Amounts and Ratios and Selected Minimum Regulatory Thresholds (Details) (USD $)	Mar. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Total risk-based capital:	'	'
Actual Amount	$836,502	$829,443
Actual Ratio	16.80%	16.80%
Adequately Capitalized Amount	397,506	396,210
Adequately Capitalized Ratio	8.00%	8.00%
Tier 1 risk-based capital:	'	'
Actual Amount	753,154	739,246
Actual Ratio	15.20%	14.90%
Adequately Capitalized Amount	198,753	198,105
Adequately Capitalized Ratio	4.00%	4.00%
Leverage capital ratio:	'	'
Actual Ratio	10.30%	10.10%
Adequately Capitalized Amount	293,212	293,414
Adequately Capitalized Ratio	4.00%	4.00%
FIB	'	'
Total risk-based capital:	'	'
Actual Amount	728,681	723,955
Actual Ratio	14.70%	14.70%
Adequately Capitalized Amount	395,309	394,038
Adequately Capitalized Ratio	8.00%	8.00%
Well Capitalized Amount	494,136	492,548
Well Capitalized Ratio	10.00%	10.00%
Tier 1 risk-based capital:	'	'
Actual Amount	657,672	650,093
Actual Ratio	13.30%	13.20%
Adequately Capitalized Amount	197,654	197,019
Adequately Capitalized Ratio	4.00%	4.00%
Well Capitalized Amount	296,482	295,529
Well Capitalized Ratio	6.00%	6.00%
Leverage capital ratio:	'	'
Actual Ratio	9.00%	8.90%
Adequately Capitalized Amount	291,961	292,199
Adequately Capitalized Ratio	4.00%	4.00%
Well Capitalized Amount	$364,952	$365,248
Well Capitalized Ratio	5.00%	5.00%

Commitments_and_Contingencies_

Commitments and Contingencies (Details) (Construction Contracts, USD $)	Mar. 31, 2014
In Thousands, unless otherwise specified
Construction Contracts	'
Unrecorded Unconditional Purchase Obligation [Line Items]	'
Commitments to Purchase	$1,050

Financial_Instruments_with_Off1

Financial Instruments with Off-Balance Sheet Risk (Details) (USD $)	Mar. 31, 2014
In Thousands, unless otherwise specified
Entity Information [Line Items]	'
Credit Extension Commitments	$1,259,320
Credit Extension Commitments, Beyond One Year	306,519
Standby Letters of Credit	'
Entity Information [Line Items]	'
Credit Extension Commitments	59,909
Unused Credit Card Lines	'
Entity Information [Line Items]	'
Credit Extension Commitments	$413,564

Supplemental_Cash_Flow_Informa

Supplemental Cash Flow Information (Details) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Supplemental Cash Flow Information [Abstract]	'	'
Transferred Loans to OREO	$3,415	$5,331
Transferred Loans to Mortgage Servicing Assets	483	1,144
Transfer from Investments	'	$429

Schedule_of_Comprehensive_Inco

Schedule of Comprehensive Income (Loss) (Details) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Change in net unrealized Gain during period:	'	'
Change in net unrealized gain during period, before tax amount	$14,351	($5,717)
Change in net unrealized gain during period, tax expense (benefit)	5,647	-2,250
Change in net unrealized gain during period, net of tax amount	8,704	-3,467
Reclassification adjustment for gains included in net income:	'	'
Reclassification adjustment for gains included in net income, before tax amount	-71	-8
Reclassification adjustment for gains included in net income, tax expense (benefit)	-28	-3
Reclassification adjustment for gains included in net income, net of tax amount	-43	-5
Change in net actuarial loss:	'	'
Change in net actuarial loss, before tax amount	35	35
Change in net actuarial loss, tax expense (benefit)	14	14
Change in net actuarial loss, net of tax amount	21	21
Other comprehensive income (loss):	'	'
Other comprehensive income (loss), before tax	14,315	-5,690
Total other comprehensive income, tax expense (benefit)	5,633	-2,239
Total other comprehensive income, net of tax amount	$8,682	($3,451)

Schedule_of_Accumulated_Other_

Schedule of Accumulated Other Comprehensive Income (Loss) (Details) (USD $)	Mar. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Net accumulated other comprehensive income:	'	'
Net unrealized gain on investment securities available-for-sale	($5,917)	($14,578)
Net actuarial loss on defined benefit post-retirement benefit plans	-1,442	-1,463
Net accumulated other comprehensive income	($7,359)	($16,041)

Schedule_of_Financial_Assets_a

Schedule of Financial Assets and Financial Liabilities Measured at Fair Value on a Recurring and Non-Recurring Basis (Details) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'	'
Real Estate Acquired Through Foreclosure, Valuation Adjustments	$0	$2,305	'
Related Allowance	7,494	'	8,929
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]	'	'	'
Mortgage servicing rights	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 of by sale	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]	'	'	'
Mortgage servicing rights	26,215	'	25,698
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 of by sale	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]	'	'	'
Mortgage servicing rights	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	48,347	'	57,302
Real Estate Acquired Through Foreclosure, Valuation Adjustments	0	2,305	'
Other real estate owned	7,748	'	8,502
Long-lived assets to be disposed of by sale	1,186	'	1,186
Related Allowance	7,493	'	8,929
Impaired Financing Receivable, Related Allowance, Partial Loan Charge-Offs	12,032	'	14,295
Impairment of Real Estate, Change in Management Estimates	'	2,305	'
Estimated Fair Value | Fair Value Measured on a Recurring Basis	'	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'	'
Mortgage servicing rights	26,215	'	25,698
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	48,347	'	57,302
Other real estate owned	7,748	'	8,502
Long-lived assets to be disposed of by sale	1,186	'	1,186
Change During Period | Fair Value Measured on a Non-recurring Basis	'	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'	'
Long-lived assets to be disposed of by sale	599	'	599
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	706,592	'	763,238
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
Obligations of U.S. government agencies | Estimated Fair Value | 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	706,592	'	763,238
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	1,186,671	'	1,184,053
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
U.S. agency residential mortgage-backed securities & collateralized mortgage obligations | Estimated Fair Value | 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	1,186,671	'	1,184,053
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	389	'	415
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
Private mortgage-backed securities | Estimated Fair Value | 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	389	'	415
Estimated Fair Value	'	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'	'
Investment securities available-for-sale	1,893,652	'	1,947,706
Mortgage servicing rights	26,215	'	25,698
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
Mortgage servicing rights	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	1,893,652	'	1,947,706
Mortgage servicing rights	26,215	'	25,698
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
Mortgage servicing rights	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	48,347	'	57,302
Carrying Amount	'	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'	'
Investment securities available-for-sale	1,893,652	'	1,947,706
Mortgage servicing rights	13,474	'	13,546
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	67,872	'	80,526
Long-lived assets to be disposed of by sale	$1,785	'	$1,785

Schedule_of_Estimated_Fair_Val

Schedule of Estimated Fair Values of Financial Instruments by Level of Valuation Inputs (Details) (USD $)	Mar. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Financial assets:	'	'
Investment securities held-to-maturity	$205,443	$205,926
Carrying Amount	'	'
Financial assets:	'	'
Cash and cash equivalents	610,531	534,827
Investment securities available-for-sale	1,893,652	1,947,706
Investment securities held-to-maturity	201,436	203,837
Accrued interest receivable	27,135	26,450
Mortgage servicing rights	13,474	13,546
Net loans	4,283,467	4,259,514
Total financial assets	7,029,695	6,985,880
Financial liabilities:	'	'
Total deposits, excluding time deposits	4,975,781	4,943,033
Time deposits	1,159,356	1,190,717
Securities sold under repurchase agreements	488,898	457,437
Other borrowed funds	9	3
Accrued interest payable	4,953	4,963
Long-term debt	36,905	36,917
Subordinated debentures held by subsidiary trusts	82,477	82,477
Total financial liabilities	6,748,379	6,715,547
Estimated Fair Value	'	'
Financial assets:	'	'
Cash and cash equivalents	610,531	534,827
Investment securities available-for-sale	1,893,652	1,947,706
Investment securities held-to-maturity	205,443	205,926
Accrued interest receivable	27,135	26,450
Mortgage servicing rights	26,215	25,698
Net loans	4,272,639	4,246,539
Total financial assets	7,035,615	6,987,146
Financial liabilities:	'	'
Total deposits, excluding time deposits	4,975,781	4,943,033
Time deposits	1,166,103	1,196,250
Securities sold under repurchase agreements	488,898	457,437
Other borrowed funds	9	3
Accrued interest payable	4,953	4,963
Long-term debt	35,200	34,508
Subordinated debentures held by subsidiary trusts	73,607	72,045
Total financial liabilities	6,744,551	6,708,239
Quoted Prices in Active Markets for Identical Assets (Level 1) | 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	0	0
Total financial assets	0	0
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
Total financial liabilities	0	0
Significant Other Observable Inputs (Level 2) | Estimated Fair Value	'	'
Financial assets:	'	'
Cash and cash equivalents	610,531	534,827
Investment securities available-for-sale	1,893,652	1,947,706
Investment securities held-to-maturity	205,443	205,926
Accrued interest receivable	27,135	26,450
Mortgage servicing rights	26,215	25,698
Net loans	4,224,292	4,189,237
Total financial assets	6,987,268	6,929,844
Financial liabilities:	'	'
Total deposits, excluding time deposits	4,975,781	4,943,033
Time deposits	1,166,103	1,196,250
Securities sold under repurchase agreements	488,898	457,437
Other borrowed funds	9	3
Accrued interest payable	4,953	4,963
Long-term debt	35,200	34,508
Subordinated debentures held by subsidiary trusts	73,607	72,045
Total financial liabilities	6,744,551	6,708,239
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	48,347	57,302
Total financial assets	48,347	57,302
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
Total financial liabilities	$0	$0

Acquisitions_Details

Acquisitions (Details) (USD $)	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2014	Mar. 31, 2014	Mar. 31, 2014	Feb. 10, 2014
In Thousands, except Share data, unless otherwise specified			Mountain West [Member]	Mountain West [Member]	Class A Common Stock	Class A Common Stock
						Mountain West [Member]
Significant Acquisitions and Disposals [Line Items]	'	'	'	'	'	'
Number of Subsidiary Banks	'	'	1	'	'	'
Number of Shared Markets	'	'	5	'	'	'
Loans held for investment	$4,326,367	$4,303,992	$405,409	'	'	'
Deposits	6,135,137	6,133,750	539,920	'	'	'
Business Acquisition Conversion Share Rate	'	'	'	'	'	0.2552
Business Acquisition Conversion Rate	'	'	'	'	'	$7.13
Share Price	'	'	'	'	$28.22	'
Estimate of Payments to Acquire Businesses, Total	'	'	'	78,814	'	'
Estimate of Payments to Acquire Businesses, Gross	'	'	'	39,920	'	'
Business Acquisitions Pending, Estimate of Equity Interest Issued or Issuable, Value Assigned	'	'	'	$38,894	'	'
Business Acquisition Pending, Equity Interest Issued or Issuable, Number of Shares	'	'	'	1,378,230	'	'

Recent_Authoritative_Accountin1

Recent Authoritative Accounting Guidance (Details) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2014
New Accounting Pronouncements or Change in Accounting Principle [Line Items]	'
Number of Investments in Other Assets, Noncurrent	2
Accounting Standards Update 2014-01 [Member] | Investment in Affordable Housing Projects [Member]	'
New Accounting Pronouncements or Change in Accounting Principle [Line Items]	'
Other Commitment, Due in Next Twelve Months	$1,434
Other Commitment, Due in Second Year	4,101
Other Commitment, Due in Third Year	25
Other Commitment, Due in Fourth Year	25
Other Commitment, Due in Fifth Year	25
Other Commitment, Due Sixth Year	25
Other Commitment, Due Seventh Year	25
Other Commitment, Due Eighth Year	25
Other Commitment, Due Ninth Year	0
Other Commitment, Due Tenth Year	15
Accounting Standards Update 2014-01 [Member] | Investment in Affordable Housing Projects [Member]	'
New Accounting Pronouncements or Change in Accounting Principle [Line Items]	'
Other Assets, Noncurrent	3,062
Current Income Tax Expense (Benefit)	$7

Subsequent_Events_Details

Subsequent Events (Details) (Common Stock [Member], Subsequent Event [Member], USD $)	Apr. 28, 2014
Common Stock [Member] | Subsequent Event [Member]	'
Subsequent Event [Line Items]	'
Dividends Payable, Amount Per Share	$0.16