Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
CASH FLOWS FROM OPERATING ACTIVITIES
Net income	$ 53,816	$ 49,438	$ 145,441	$ 145,510
Adjustments to reconcile net income to net cash provided by operating activities:
Provision for credit losses	21,000	8,000	55,000	17,500
Depreciation and amortization			34,121	35,788
Addition to (recovery of) valuation allowance on mortgage servicing rights, net			2,486	(306)
Amortization of mortgage servicing rights			9,142	8,902
Amortization of other intangible assets	525	885	1,568	2,574
Amortization and accretion on earning assets, funding, and other, net			34,077	29,039
Tax benefit of stock based compensation			802	2,093
Gain on sales of investment securities, net			(6,201)	(4,038)
(Gain) loss on sales of assets and impairment write-downs, net	1,034	(244)	853	(2,931)
Gain on mortgage banking activities, net			(21,741)	(15,504)
Mortgage loans originated and acquired for sale			(983,930)	(911,133)
Proceeds from sales of mortgage loans held for sale			1,147,278	941,575
(Increase) decrease in interest receivable			(5,809)	(3,404)
Increase (decrease) in interest payable			(5,994)	(2,642)
Net change in other assets and other liabilities			576	(19,018)
Net cash provided by operating activities			407,669	224,005
CASH FLOWS FROM INVESTING ACTIVITIES
Net increase in loans			(1,461,884)	(935,208)
Purchases of:
Available for sale securities			(849,466)	(2,075,062)
Held to maturity securities			(151,556)	(207,139)
Federal Home Loan Bank and Federal Reserve Bank stocks			(72,975)	(14,279)
Premises, equipment, and software, net of disposals			(90,691)	(36,778)
Other assets			(4,628)	(9,903)
Proceeds from:
Sales of available for sale securities			359,591	1,066,957
Sales of Federal Home Loan Bank stock			80,000	42,514
Prepayments, calls, and maturities of available for sale investment securities			651,403	869,635
Prepayments, calls, and maturities of held to maturity investment securities			55,579	7,190
Sales, prepayments, calls, and maturities of other assets			19,351	17,793
Net cash (paid) received in acquisition			(685)	1,132
Net cash used in investing activities			(1,465,961)	(1,273,148)
CASH FLOWS FROM FINANCING ACTIVITIES
Net increase in deposits			740,047	1,794,891
Net increase (decrease) in short-term funding			405,677	(45,953)
Repayment of long-term funding			(1,180,027)	(1,500,026)
Proceeds from issuance of long-term funding			1,265,000	250,000
Proceeds from issuance of common stock for stock-based compensation plans			7,749	15,373
Proceeds from issuance of preferred stock			97,066	62,966
Redemption of preferred stock			(58,903)	0
Purchase of preferred stock			(1,248)	(1,335)
Purchase of common stock returned to authorized but unissued			(20,007)	(93,000)
Purchase of treasury stock			(4,243)	(5,070)
Cash dividends on common stock			(49,642)	(45,599)
Cash dividends on preferred stock			(6,555)	(4,957)
Net cash provided by financing activities			1,194,914	427,290
Total other comprehensive income (loss)	14,707	(12,782)	(31,362)	(20,226)
Net increase (decrease) in cash and cash equivalents			136,622	(621,853)
Cash and cash equivalents at beginning of period			473,685	1,032,067	$ 1,032,067
Cash and cash equivalents at end of period	610,307	410,214	610,307	410,214	$ 473,685
Supplemental disclosures of cash flow information:
Cash paid for interest			68,371	59,751
Cash paid for income and franchise taxes			53,126	58,975
Loans and bank premises transferred to other real estate owned			8,834	5,782
Capitalized mortgage servicing rights			8,701	9,853
Loans transferred into held for sale from portfolio, net			256,188	0
Unsettled trades to sell securities	0	139,286	0	139,286
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