Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Operating Activities
Net income per consolidated statements of income	$ 108,411	$ 116,038	$ 123,562
Adjustments to reconcile net income to net cash provided by operating activities:
Provision for loan losses, net	14,714	11,800	7,382
Depreciation and amortization	36,613	37,056	36,072
Net amortization of securities	9,664	7,793	7,701
Securities losses (gains), net	310	0	(300)
Gains on sales of loans, net	(20,531)	(17,953)	(10,762)
Deferred income tax provision	18,000	14,800	18,700
Proceeds from sales of loans held for sale	1,404,852	1,264,303	924,289
Purchases and originations of loans held for sale	(1,392,155)	(1,279,321)	(893,569)
Originations of mortgage servicing rights	(16,745)	(17,598)	(12,293)
Earnings on bank-owned life insurance	(4,883)	(4,824)	(4,728)
Net (increase) decrease in other assets	(20,129)	28,794	4,886
Net increase (decrease) in other liabilities	7,284	6,608	(6,010)
Other operating activities, net	2,022	4,391	16,337
Net cash provided by operating activities	147,427	171,887	211,267
Investing Activities
Proceeds from maturities, prepayments and calls of securities held to maturity	277,373	126,546	93,471
Proceeds from maturities, prepayments and calls of securities available for sale	486,915	479,927	405,186
Proceeds from sales of securities available for sale	24,693	0	56,814
Purchases of securities held to maturity	(239,446)	(107,679)	(90,114)
Purchases of securities available for sale	(547,112)	(504,920)	(631,713)
Net proceeds from bank-owned life insurance	2,585	648	0
Net (increase) decrease in federal funds sold and securities purchased under reverse repurchase agreements	(250)	1,635	5,368
Net increase in member bank stock	(8,386)	(18,480)	0
Net increase in loans	(677,296)	(528,050)	(437,240)
Purchases of premises and equipment	(10,208)	(12,757)	(12,389)
Proceeds from sales of premises and equipment	6,799	3,061	4,641
Proceeds from sales of other real estate	42,809	48,898	48,119
Purchases of software	(8,024)	(8,741)	0
Investments in tax credit and other partnerships	(116)	(4,578)	(5,435)
Distributions received for investments in tax credit and other partnerships	0	0	7,037
Purchase of insurance book of business	0	(2,787)	0
Net cash used in investing activities	(649,664)	(527,277)	(556,255)
Financing Activities
Net increase (decrease) in deposits	467,782	(110,128)	(161,544)
Net increase (decrease) in federal funds purchased and securities sold under repurchase agreements	98,775	(2,501)	191,956
Net (decrease) increase in short-term borrowings	(150,748)	(7,293)	348,920
Proceeds from long-term FHLB advances	250,000	500,000	0
Payments on long-term FHLB advances	(94)	(94)	(156)
Payment of subordinated debt	(50,000)	0	0
Common stock dividends	(62,666)	(62,605)	(62,474)
Common stock issued-net, long-term incentive plan	0	0	(1,307)
Repurchase and retirement of common stock	(750)	0	0
Excess tax expense from stock-based compensation arrangements	(107)	(211)	(195)
Net cash provided by financing activities	552,192	317,168	315,200
Increase (Decrease) in cash and cash equivalents	49,955	(38,222)	(29,788)
Cash and cash equivalents at beginning of year	277,751	315,973	345,761
Cash and cash equivalents at end of year	$ 327,706	$ 277,751	$ 315,973