Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating Activities
Net income per consolidated statements of income	$ 105,630	$ 108,411	$ 116,038
Adjustments to reconcile net income to net cash provided by operating activities:
Provision for loan losses, net	7,699	14,714	11,800
Depreciation and amortization	38,471	36,613	37,056
Net amortization of securities	10,964	9,664	7,793
Securities (gains) losses, net	(15)	310	0
Gains on sales of loans, net	(18,933)	(20,531)	(17,953)
Deferred income tax provision	26,068	18,000	14,800
Proceeds from sales of loans held for sale	1,197,821	1,404,852	1,264,303
Purchases and originations of loans held for sale	(1,179,187)	(1,392,155)	(1,279,321)
Originations of mortgage servicing rights	(15,860)	(16,745)	(17,598)
Earnings on bank-owned life insurance	(5,025)	(4,883)	(4,824)
Net change in other assets	23,451	(20,129)	28,794
Net change in other liabilities	9,093	7,284	6,608
Other operating activities, net	6,430	2,932	5,043
Net cash provided by operating activities	206,607	148,337	172,539
Investing Activities
Proceeds from maturities, prepayments and calls of securities held to maturity	174,976	277,373	126,546
Proceeds from maturities, prepayments and calls of securities available for sale	467,194	486,915	479,927
Proceeds from sales of securities available for sale	27,682	24,693	0
Purchases of securities held to maturity	(69,989)	(239,446)	(107,679)
Purchases of securities available for sale	(346,159)	(547,112)	(504,920)
Net proceeds from bank-owned life insurance	3,623	2,585	648
Net change in federal funds sold and securities purchased under reverse repurchase agreements	6,785	(250)	1,635
Net change in member bank stock	4,474	(8,386)	(18,480)
Net change in loans	(608,886)	(677,296)	(528,050)
Purchases of premises and equipment	(13,219)	(10,208)	(12,757)
Proceeds from sales of premises and equipment	8,377	6,799	3,061
Proceeds from sales of other real estate	26,849	42,809	48,898
Purchases of software	(5,498)	(8,024)	(8,741)
Investments in tax credit and other partnerships	(5,296)	(116)	(4,578)
Purchase of insurance book of business	0	0	(2,787)
Net cash used in business acquisition	(19,775)	0	0
Net cash used in investing activities	(348,862)	(649,664)	(527,277)
Financing Activities
Net change in deposits	355,342	467,782	(110,128)
Net change in federal funds purchased and securities sold under repurchase agreements	(69,990)	98,775	(2,501)
Net change in short-term borrowings	(67,451)	(150,748)	(7,293)
Payments on long-term FHLB advances	(65)	(94)	(94)
Proceeds from long-term FHLB advances	0	250,000	500,000
Redemption of junior subordinated debt securities	(3,000)	0	0
Payment of subordinated debt	0	(50,000)	0
Common stock dividends	(62,795)	(62,666)	(62,605)
Repurchase and retirement of common stock	0	(750)	0
Shares withheld to pay taxes, long-term incentive plan	(1,724)	(1,017)	(863)
Net cash provided by financing activities	150,317	551,282	316,516
Net change in cash and cash equivalents	8,062	49,955	(38,222)
Cash and cash equivalents at beginning of year	327,706	277,751	315,973
Cash and cash equivalents at end of year	$ 335,768	$ 327,706	$ 277,751