Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Operating Activities
Net income per consolidated statements of income	$ 116,038	$ 123,562	$ 117,060
Adjustments to reconcile net income to net cash provided by operating activities:
Provision for loan losses, net	11,800	7,382	(7,382)
Depreciation and amortization	37,056	36,072	37,153
Net amortization of securities	7,793	7,701	6,427
Securities gains, net	0	(300)	(485)
Gains on sales of loans, net	(17,953)	(10,762)	(26,422)
Deferred income tax provision	14,800	18,700	21,163
Proceeds from sales of loans held for sale	1,264,303	924,289	1,383,967
Purchases and originations of loans held for sale	(1,279,321)	(893,569)	(1,270,460)
Originations and sales of mortgage servicing rights, net	(17,598)	(12,293)	(18,481)
Increase in bank-owned life insurance	(4,824)	(4,728)	(1,446)
Net decrease in other assets	28,794	4,886	54,885
Net increase (decrease) in other liabilities	6,608	(6,010)	(2,319)
Other operating activities, net	4,391	16,337	7,523
Net cash provided by operating activities	171,887	211,267	301,183
Investing Activities
Proceeds from calls and maturities of securities held to maturity	126,546	93,471	13,374
Proceeds from calls and maturities of securities available for sale	479,927	405,186	766,858
Proceeds from sales of securities available for sale	0	56,814	227,930
Purchases of securities held to maturity	(107,679)	(90,114)	(35,045)
Purchases of securities available for sale	(504,920)	(631,713)	(1,227,860)
Net proceeds from (purchases of) bank-owned life insurance	648	0	(100,000)
Net decrease (increase) in federal funds sold and securities purchased under reverse repurchase agreements	1,635	5,368	(207)
Net increase in member bank stock	(18,480)	0	0
Net (increase) decrease in loans	(528,050)	(437,240)	18,266
Purchases of premises and equipment	(12,757)	(12,389)	(15,989)
Proceeds from sales of premises and equipment	3,061	4,641	4,168
Proceeds from sales of other real estate	48,898	48,119	46,267
Purchases of software	(8,741)	0	0
Investments in tax credit and other partnerships	(4,578)	(5,435)	(45,766)
Distributions received for investments in tax credit and other partnerships	0	7,037	0
Net cash received in business combination	0	0	89,037
Purchase of insurance book of business	(2,787)	0	0
Net cash provided by (used in) investing activities	(527,277)	(556,255)	(258,967)
Financing Activities
Net (decrease) increase in deposits	(110,128)	(161,544)	223,131
Net (decrease) increase in federal funds purchased and securities sold under repurchase agreements	(2,501)	191,956	(37,242)
Net (decrease) increase in short-term borrowings	(7,293)	348,920	(20,858)
Proceeds from long-term FHLB advances	500,000	0	0
Payments on long-term FHLB advances	(94)	(156)	(531)
Redemption of junior subordinated debt securities	0	0	(33,000)
Common stock dividends	(62,605)	(62,474)	(62,276)
Common stock issued-net, long-term incentive plan	0	(1,307)	3,640
Excess tax expense from stock-based compensation arrangements	(211)	(195)	(808)
Net cash (used in) provided by financing activities	317,168	315,200	72,056
(Decrease) Increase in cash and cash equivalents	(38,222)	(29,788)	114,272
Cash and cash equivalents at beginning of year	315,973	345,761	231,489
Cash and cash equivalents at end of year	$ 277,751	$ 315,973	$ 345,761