Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
CASH FLOWS FROM OPERATING ACTIVITIES
Net income	$ 57,983	$ 49,091	$ 114,253	$ 91,625
Adjustments to reconcile net income to net cash provided by operating activities:
Provision for credit losses	12,000	14,000	21,000	34,000
Depreciation and amortization			23,241	22,914
Addition to valuation allowance on mortgage servicing rights, net			275	2,120
Amortization of mortgage servicing rights			5,084	5,896
Amortization of other intangible assets	496	539	1,009	1,043
Amortization and accretion on earning assets, funding, and other, net			17,889	22,045
Tax impact of stock based compensation			4,035	395
Gain on sales of investment securities, net			(356)	(6,214)
Asset (gains) losses, net	466	343	700	(181)
(Gain) loss on mortgage banking activities, net			4,287	(7,058)
Mortgage loans originated and acquired for sale			(220,284)	(517,838)
Proceeds from sales of mortgage loans held for sale			364,128	491,980
Increase in interest receivable			(757)	(4,875)
Increase (decrease) in interest payable			2,653	(4,739)
Commercial loans held for sale
Other, net			(38,650)	(25,836)
Net cash provided by operating activities			298,507	105,277
CASH FLOWS FROM INVESTING ACTIVITIES
Net increase in loans			(819,198)	(1,281,291)
Purchases of:
Available for sale securities			(417,397)	(495,453)
Held to maturity securities			(70,969)	(112,226)
Federal Home Loan Bank and Federal Reserve Bank stocks			(166,869)	(67,261)
Premises, equipment, and software, net of disposals			(19,289)	(81,461)
Other assets			(6,498)	(3,073)
Proceeds from:
Sales of available for sale securities			0	359,484
Sales of held to maturity securities			16,059	0
Proceeds from Sale of Federal Home Loan Bank Stock			125,690	20,000
Prepayments, calls, and maturities of available for sale investment securities			389,251	371,440
Prepayments, calls, and maturities of held to maturity investment securities			80,976	37,172
Sales, prepayments, calls, and maturities of other assets			6,353	13,362
Net cash paid in acquisition			(217)	(685)
Net cash used in investing activities			(882,108)	(1,239,992)
CASH FLOWS FROM FINANCING ACTIVITIES
Net decrease in deposits			(270,268)	(714,815)
Proceeds from (Repayments of) Short-term Debt			310,447	1,077,141
Proceeds from (Repayments of) Long-term Debt and Capital Securities			(12)	(430,018)
Proceeds from issuance of long-term funding			500,000	1,265,000
Proceeds from issuance of common stock for stock-based compensation plans			20,945	4,276
Purchase of preferred stock			0	(1,248)
Purchase of common stock returned to authorized but unissued			0	(20,007)
Purchase of treasury stock for tax withholding			(8,445)	(4,018)
Cash dividends on common stock			(36,804)	(33,034)
Cash dividends on preferred stock			(4,669)	(4,367)
Net cash provided by financing activities			511,194	1,138,910
Net increase (decrease) in cash and cash equivalents			(72,407)	4,195
Cash and cash equivalents at beginning of period			642,233	473,685	$ 473,685
Cash and cash equivalents at end of period	569,826	477,880	569,826	477,880	$ 642,233
Supplemental disclosures of cash flow information:
Cash paid for interest			57,306	46,316
Cash paid for income taxes			27,461	27,852
Loans and bank premises transferred to other real estate owned			3,267	4,704
Capitalized mortgage servicing rights			3,278	4,149
Loans transferred into held for sale from portfolio, net			62,264	130,694
Fair value of assets acquired, including cash and cash equivalents	0	522	0	522
Fair value ascribed to goodwill and intangible assets	217	4,119	217	4,119
Fair value of liabilities assumed	$ 0	$ 1,423	$ 0	$ 1,423