Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash Flows from Operating Activities
Net income	$ 229,264	$ 200,274	$ 188,301
Adjustments to reconcile net income to net cash provided by operating activities:
Provision for credit losses	26,000	70,000	37,500
Depreciation and amortization	46,967	45,434	47,168
Addition to (recovery of) valuation allowance on mortgage servicing rights, net	175	(200)	(425)
Amortization of mortgage servicing rights	10,084	12,327	11,601
Amortization of other intangible assets	1,959	2,093	3,094
Amortization and accretion on earning assets, funding, and other, net	37,476	46,615	39,806
Net amortization of tax credit investments	19,834	5,272	3,100
Deferred income taxes	21,402	10,656	(3,522)
Gain on sales of investment securities, net	(434)	(9,316)	(8,133)
Asset (gains) losses, net	1,244	86	(2,540)
Gain on mortgage banking activities, net	(3,516)	(27,060)	(20,258)
Mortgage loans originated and acquired for sale	(715,357)	(1,271,124)	(1,228,106)
Proceeds from sales of mortgage loans held for sale	819,950	1,542,660	1,241,012
Pension contributions	(6,242)	0	0
(Increase) decrease in interest receivable	(9,476)	(7,836)	395
Increase (decrease) in interest payable	6,535	(4,642)	3,898
Net change in other assets and other liabilities	(27,497)	26,144	(11,685)
Net cash provided by operating activities	458,368	641,383	301,206
Cash Flows from Investing Activities
Net increase in loans	(861,934)	(1,682,579)	(1,136,793)
Purchases of
Available for sale securities	(1,137,191)	(1,304,921)	(2,859,793)
Held to maturity securities	(234,379)	(195,442)	(250,767)
Federal Home Loan Bank and Federal Reserve Bank stocks	(262,986)	(92,761)	(35,647)
Premises, equipment, and software, net of disposals	(47,369)	(103,881)	(54,636)
Proceeds from
Sales of available for sale securities	18,467	549,555	1,601,947
Sale of Federal Home Loan Bank and Federal Reserve Bank stocks	237,656	100,000	77,514
Prepayments, calls, and maturities of available for sale securities	713,486	997,701	1,099,625
Prepayments, calls, and maturities of held to maturity securities	210,753	75,796	17,013
Prepayments, calls and maturities of other assets	20,070	27,692	21,236
Net change in tax credit investments	(53,770)	(23,498)	(14,649)
Net cash (paid) received in acquisition	339	(685)	1,132
Net cash used in investing activities	(1,396,858)	(1,653,023)	(1,533,818)
Cash Flows from Financing Activities
Net increase in deposits	897,514	880,783	2,244,161
Net increase (decrease) in short-term funding	(415,753)	257,619	(233,872)
Repayment of long-term funding	(115,020)	(1,180,038)	(1,500,035)
Proceeds from issuance of long-term funding	750,000	1,265,000	250,000
Proceeds from issuance of common stock for stock-based compensation plans	27,619	21,748	20,054
Proceeds from issuance of preferred stock	0	97,066	62,966
Redemption of preferred stock	0	(58,903)	0
Purchase of preferred stock	0	(1,248)	(1,335)
Purchase of common stock returned to authorized but unissued	(37,031)	(20,007)	(93,000)
Purchase of treasury stock for tax withholding	(9,290)	(5,074)	(5,154)
Cash dividends on common stock	(76,417)	(67,855)	(62,400)
Cash dividends on preferred stock	(9,347)	(8,903)	(7,155)
Net cash provided by financing activities	1,012,275	1,180,188	674,230
Net increase (decrease) in cash and cash equivalents	73,785	168,548	(558,382)
Cash and cash equivalents at beginning of period	642,233	473,685	1,032,067
Cash and cash equivalents at end of period	716,018	642,233	473,685
Supplemental disclosures of cash flow information
Cash paid for interest	138,174	88,269	73,054
Cash paid for income and franchise taxes	81,450	75,558	84,407
Loans and bank premises transferred to other real estate owned	11,505	9,752	10,988
Capitalized mortgage servicing rights	7,167	12,262	12,372
Loans transferred into held for sale from portfolio, net	71,954	256,194	0
Supplemental Cash Flow - Acquisition Information
Fair value of assets acquired, including cash and cash equivalents	647	522	4,590
Fair value ascribed to goodwill and intangible assets	6,450	4,119	51,791
Fair value of liabilities assumed	54	1,423	12,851
Common stock issued in acquisition	$ 7,151	$ 0	$ 43,530