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	$ 123,562	$ 117,060	$ 117,283
Adjustments to reconcile net income to net cash provided by operating activities:
Provision for loan losses, net	7,382	(7,382)	12,294
Depreciation and amortization	36,072	37,153	29,275
Net amortization of securities	7,701	6,427	7,008
Securities gains, net	(300)	(485)	(1,059)
Gains on sales of loans, net	(10,762)	(26,422)	(33,918)
Bargain purchase gain on acquisitions	0	0	(3,635)
Deferred income tax provision (benefit)	18,700	21,163	(8,452)
Proceeds from sales of loans held for sale	924,289	1,383,967	1,849,712
Purchases and originations of loans held for sale	(893,569)	(1,270,460)	(1,856,293)
Originations and sales of mortgage servicing rights, net	(12,293)	(18,481)	(23,253)
Increase in bank-owned life insurance	(4,728)	(1,446)	(423)
Net decrease (increase) in other assets	4,886	54,885	(15,241)
Net (decrease) increase in other liabilities	(6,010)	(2,319)	16,482
Other operating activities, net	16,337	7,523	22,497
Net cash provided by operating activities	211,267	301,183	112,277
Investing Activities
Proceeds from calls and maturities of securities held to maturity	93,471	13,374	15,534
Proceeds from calls and maturities of securities available for sale	405,186	766,858	917,316
Proceeds from sales of securities available for sale	56,814	227,930	34,826
Purchases of securities held to maturity	(90,114)	(35,045)	0
Purchases of securities available for sale	(631,713)	(1,227,860)	(1,122,480)
Purchase of bank owned life insurance	0	(100,000)	0
Net decrease (increase) in federal funds sold and securities purchased under reverse repurchase agreements	5,368	(207)	2,212
Net (increase) decrease in loans	(437,240)	18,266	250,508
Purchases of premises and equipment	(12,389)	(15,989)	(17,172)
Proceeds from sales of premises and equipment	4,641	4,168	4
Proceeds from sales of other real estate	48,119	46,267	34,992
Investments in tax credit and other partnerships	(5,435)	(45,766)	(20,152)
Distributions received for investments in tax credit and other partnerships	7,037	0	0
Net cash received in business combination	0	89,037	78,151
Net cash (used in) provided by investing activities	(556,255)	(258,967)	173,739
Financing Activities
Net (decrease) increase in deposits	(161,544)	223,131	121,358
Net increase (decrease) in federal funds purchased and securities sold under repurchase agreements	191,956	(37,242)	(315,671)
Net increase (decrease) in short-term borrowings	348,920	(20,858)	(1,641)
Payments on long-term FHLB advances	(156)	(531)	0
Redemption of junior subordinated debt securities	0	(33,000)	0
Common stock dividends	(62,474)	(62,276)	(59,961)
Common stock issued-net, long-term incentive plan	(1,307)	3,640	(1,318)
Excess tax (expense) benefit from stock-based compensation arrangements	(195)	(808)	81
Net cash provided by (used in) financing activities	315,200	72,056	(257,152)
(Decrease) Increase in cash and cash equivalents	(29,788)	114,272	28,864
Cash and cash equivalents at beginning of year	345,761	231,489	202,625
Cash and cash equivalents at end of year	$ 315,973	$ 345,761	$ 231,489