Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Cash Flows From Operating Activities: [Abstract]
Net income	$ 232,281	$ 292,259	$ 295,479
Adjustments to reconcile net income to net cash provided by (used in) operating activities: [Abstract]
Provision for credit losses	65,000	34,000	0
Change in fair value of mortgage servicing rights due to market changes	2,193	4,853	16,445
Change in fair value of mortgage servicing rights due to loan runoff	40,744	28,064	19,325
Unrealized losses (gains) from derivative contracts	11,234	964	(6,495)
Depreciation and amortization	47,016	37,918	36,707
Tax effect from equity compensation, net	(1,505)	(925)	(8,258)
Share-based compensation	10,471	12,083	9,680
Net amortization of securities discounts and premiums	41,643	55,145	57,202
Net realized gains on financial instruments and other assets	(13,011)	(15,212)	(1,362)
Net gain on mortgage loans held for sale	(63,636)	(75,780)	(62,053)
Mortgage loans originated for sale	(6,117,417)	(6,372,956)	(4,484,394)
Proceeds from sale of mortgage loans held for sale	6,193,587	6,446,659	4,441,819
Capitalized mortgage servicing rights	(71,405)	(79,546)	(54,413)
Change in trading and fair value option securities	149,921	(69,298)	(243,265)
Change in receivables	(603,861)	(6,943)	(7,103)
Change in other assets	(49,565)	(29,548)	68,821
Change in accrued interest, taxes and expense	44,269	17,517	(115,772)
Change in other liabilities	(11,413)	15,756	1,007
Net cash provided by (used in) operating activities	(93,454)	295,010	(36,630)
Cash Flows From Investing Activities: [Abstract]
Proceeds from sales of available for sale securities	899,381	1,600,380	2,664,740
Proceeds from maturities or redemptions of investment securities	86,847	72,664	63,258
Proceeds from maturities or redemptions of available for sale securities	1,740,226	1,542,517	1,635,533
Purchases of investment securities	(41,590)	(25,132)	(44,723)
Purchases of available for sale securities	(2,333,740)	(3,300,601)	(3,045,077)
Change in amount receivable on unsettled securities sales	33,005	34,066	(57,085)
Loans originated, net of principal collected	(621,605)	(1,681,035)	(1,346,995)
Net payments on derivative asset contracts	(103,668)	(156,419)	(247,726)
Proceeds from disposition of assets	198,922	195,760	273,271
Acquisitions, net of cash acquired	56,017	(18,098)	(21,898)
Purchases of assets	(199,802)	(265,406)	(307,318)
Net cash used in investing activities	(286,007)	(2,001,304)	(434,020)
Cash Flows From Financing Activities: [Abstract]
Net change in demand deposits, transaction deposits and savings accounts	1,277,285	149,951	958,809
Net change in time deposits	(216,084)	(202,652)	(87,277)
Net change in other borrowed funds	(606,476)	2,547,688	511,776
Repayment of subordinated debentures	226,550	121,810	0
Issuance of subordinated debentures, net of issuance costs	144,615	0	0
Change in amount due on unsettled security purchases	(10,389)	(273,643)	244,800
Issuance of common and treasury stock, net	12,455	6,711	4,472
Net change in derivative margin accounts	(28,806)	(43,226)	84,365
Net payments or proceeds on derivative liability contracts	106,051	149,428	257,439
Tax effect from equity compensation, net	1,505	925	8,258
Sale of non-controlling interests	0	5,500	0
Repurchase of common stock	(66,792)	(229,540)	(12,337)
Dividends paid	(113,455)	(115,281)	(111,026)
Net cash provided by financing activities	273,359	1,874,051	1,859,279
Net increase (decrease) in cash and cash equivalents	(106,102)	167,757	1,388,629
Cash and cash equivalents at beginning of period	2,643,599	2,475,842	1,087,213
Cash and cash equivalents at end of period	2,537,497	2,643,599	2,475,842
Supplemental Cash Flow Information: [Abstract]
Cash paid for interest	82,876	66,091	65,721
Cash paid for taxes	79,883	101,991	67,199
Net loans and bank premises transferred to repossessed real estate and other assets	36,391	12,592	79,464
Residential mortgage loans guaranteed by U.S. government agencies that became eligible for repurchase during the period	120,406	123,383	144,630
Conveyance of other real estate owned guaranteed by U.S. government agencies	68,873	110,505	44,963
Issuance of shares in settlement of accrued executive compensation	$ 0	$ 0	$ 8,352