Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Operating Activities
Net income	$ 112,755	$ 95,644	$ 75,516
Adjustments to reconcile net income to net cash provided by operating activities:
Provision for loan losses	1,912	6,887	21,525
Net amortization of investment securities premiums and discounts	27,491	64,066	71,992
Loans held for sale originated or acquired	(669,144)	(918,451)	(1,188,632)
Proceeds from sales of loans held for sale	705,178	1,084,799	1,204,431
Gain on sale of loans	(19,797)	(28,517)	(32,227)
Loss on sale of investments	188	299	0
Bargain purchase gain	(680)	0	0
Stock-based compensation expense, net of tax benefits	859	1,011	254
Excess tax (benefits) deficiencies from stock-based compensation	(138)	223	8
Depreciation of premises and equipment	12,108	10,485	10,615
(Gain) loss on sale of other real estate owned and write-downs, net	(937)	1,450	13,311
Core deposit intangible amortization	2,811	2,401	2,110
Deferred tax benefit	5,931	4,633	837
Net decrease (increase) in accrued interest receivable	2,648	(265)	(2,809)
Net (increase) decrease in other assets	(5,702)	19,881	(3,291)
Net decrease (increase) in accrued interest payable	567	(1,354)	(1,150)
Net increase (decrease) in other liabilities	6,684	(9,097)	11,303
Net cash provided by operating activities	182,734	334,095	183,793
Investing Activities
Sales of available-for-sale securities	169,372	181,971	0
Maturities, prepayments and calls of available-for-sale securities	628,238	1,682,363	2,041,416
Purchases of available-for-sale securities	(281,332)	(1,426,262)	(2,638,054)
Maturities, prepayments and calls of held-to-maturity securities	8,930	0	0
Purchases of held-to-maturity securities	(49,691)	0	0
Principal collected on loans	1,418,517	1,224,222	1,034,374
Loans originated or acquired	(1,735,155)	(1,559,353)	(1,049,344)
Net addition of premises and equipment and other real estate owned	(14,389)	(8,977)	(10,730)
Proceeds from sale of other real estate owned	15,714	28,535	41,804
Net sale of non-marketable equity securities	801	583	888
Net cash (paid) received in acquisitions	(2,112)	26,155	0
Net cash provided by (used in) investing activities	158,893	149,237	(579,646)
Financing Activities
Net increase (decrease) in deposits	455,604	(334,672)	543,248
Net increase in securities sold under agreements to repurchase	83,713	23,886	30,865
Net decrease in Federal Home Loan Bank advances	(543,238)	(162,298)	(72,033)
Net decrease (increase) in other borrowed funds	(933)	(1,502)	180
Cash dividends paid	(50,944)	(44,232)	(47,472)
Excess tax benefits (deficiencies) from stock-based compensation	138	(223)	(8)
Stock-based compensation activity	785	4,326	81
Net cash (used in) provided by financing activities	(54,875)	(514,715)	454,861
Net increase (decrease) in cash and cash equivalents	286,752	(31,383)	59,008
Cash and cash equivalents at beginning of period	155,657	187,040	128,032
Cash and cash equivalents at end of period	442,409	155,657	187,040
Supplemental Disclosure of Cash Flow Information
Cash paid during the period for interest	26,398	30,111	36,865
Cash paid during the period for income taxes	33,343	23,576	21,257
Supplemental Disclosure of Non-Cash Investing Activities
Transfer of investment securities from available-for-sale to held-to-maturity	484,583	0	0
Sale and refinancing of other real estate owned	1,361	4,819	5,659
Transfer of loans to other real estate owned	11,493	15,266	27,536
Fair value of common stock shares issued	15,127	45,033	0
Cash consideration for outstanding shares	16,690	24,858	0
Fair value of assets acquired	349,167	630,569	0
Liabilities assumed	$ 316,670	$ 560,678	$ 0