Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
CASH FLOWS FROM OPERATING ACTIVITIES
Net income	$ 49,091	$ 49,400	$ 91,625	$ 96,072
Adjustments to reconcile net income to net cash provided by operating activities:
Provision for credit losses	14,000	5,000	34,000	9,500
Depreciation and amortization			22,914	24,232
(Recovery of) addition to valuation allowance on mortgage servicing rights, net			2,120	(465)
Amortization of mortgage servicing rights			5,896	6,147
Amortization of other intangible assets	539	888	1,043	1,689
Amortization and accretion on earning assets, funding, and other, net			22,045	19,457
Tax impact of stock based compensation			395	1,784
Gain on sales of investment securities, net			(6,214)	(1,242)
Gain on sales of assets and impairment write-downs, net	343	(1,854)	(181)	(2,687)
Gain on mortgage banking activities, net			(7,058)	(8,000)
Mortgage loans originated and acquired for sale			(517,838)	(619,202)
Proceeds from sales of mortgage loans held for sale			491,980	599,262
(Increase) decrease in interest receivable			(4,875)	808
Increase (decrease) in interest payable			(4,739)	5,596
Net change in other assets and other liabilities			(25,836)	(33,825)
Net cash provided by operating activities			105,277	99,126
CASH FLOWS FROM INVESTING ACTIVITIES
Net increase in loans			(1,281,291)	(703,636)
Purchases of:
Available for sale securities			(495,453)	(1,702,678)
Held to maturity securities			(112,226)	(133,976)
Federal Home Loan Bank and Federal Reserve Bank stocks			(67,261)	(14,172)
Premises, equipment, and software, net of disposals			(81,461)	(26,232)
Other assets			(3,073)	(8,183)
Proceeds from:
Sales of available for sale securities			359,484	1,065,328
Sales of Federal Home Loan Bank stock			20,000	42,514
Prepayments, calls, and maturities of available for sale investment securities			371,440	620,320
Prepayments, calls, and maturities of held to maturity investment securities			37,172	6,290
Sales, prepayments, calls, and maturities of other assets			13,362	10,465
Net cash (paid) received in acquisition			(685)	1,132
Net cash used in investing activities			(1,239,992)	(842,828)
CASH FLOWS FROM FINANCING ACTIVITIES
Net increase (decrease) in deposits			(714,815)	506,059
Net increase in short-term funding			1,077,141	527,248
Repayment of long-term funding			(430,018)	(1,000,017)
Proceeds from issuance of long-term funding			1,265,000	250,000
Proceeds from issuance of common stock for stock-based compensation plans			4,276	13,704
Proceeds from issuance of preferred stock			0	62,966
Purchase of preferred stock			(1,248)	(752)
Purchase of common stock returned to authorized but unissued			(20,007)	(93,000)
Purchase of treasury stock			(4,018)	(4,500)
Cash dividends on common stock			(33,034)	(30,508)
Cash dividends on preferred stock			(4,367)	(2,773)
Net cash provided by financing activities			1,138,910	228,427
Net increase (decrease) in cash and cash equivalents			4,195	(515,275)
Cash and cash equivalents at beginning of period			473,685	1,032,067	$ 1,032,067
Cash and cash equivalents at end of period	477,880	516,792	477,880	516,792	$ 473,685
Supplemental disclosures of cash flow information:
Cash paid for interest			46,316	32,123
Cash paid for income taxes			27,852	40,473
Loans and bank premises transferred to other real estate owned			4,704	3,117
Capitalized mortgage servicing rights			4,149	6,729
Loans transferred into held for sale from portfolio, net			130,694	0
Fair value of assets acquired, including cash and cash equivalents	522	4,590	522	4,590
Fair value ascribed to goodwill and intangible assets	4,119	51,791	4,119	51,791
Fair value of liabilities assumed	$ 1,423	$ 12,851	1,423	12,851
Common stock issued in acquisition			$ 0	$ 43,530