Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Cash Flows From Operating Activities: [Abstract]
Net income	$ 500,685	$ 446,424	$ 335,685
Adjustments to reconcile net income to net cash provided by (used in) operating activities: [Abstract]
Provision for credit losses	44,000	8,000	(7,000)
Change in fair value of mortgage servicing rights due to market changes	53,517	(4,668)	(172)
Change in fair value of mortgage servicing rights due to principal payments	38,979	33,528	33,527
Net unrealized losses (gains) from derivative contracts	(25,936)	4,686	3,704
Share-based compensation	15,544	4,229	23,602
Depreciation and amortization	95,416	60,843	54,466
Net amortization of discounts and premiums	(16,984)	30,945	28,693
Net losses (gains) on financial instruments and other losses (gains), net	(583)	9,585	(2,828)
Net gain on mortgage loans held for sale	(40,402)	(35,705)	(47,159)
Mortgage loans originated for sale	(3,025,930)	(2,587,297)	(3,286,873)
Proceeds from sale of mortgage loans held for sale	3,035,600	2,691,144	3,405,890
Capitalized mortgage servicing rights	(35,128)	(35,247)	(39,149)
Change in trading and fair value option securities	(483,007)	(1,023,097)	(804,204)
Change in receivables	(740,868)	(38,346)	321,880
Change in other assets	18,955	27,507	(5,506)
Change in accrued interest, taxes and expense	34,894	(5,191)	18,191
Change in other liabilities	57,569	(139,346)	182,184
Net cash provided by (used in) operating activities	(473,679)	(552,006)	214,931
Cash Flows From Investing Activities: [Abstract]
Proceeds from maturities or redemptions of investment securities	60,128	124,864	112,022
Proceeds from maturities or redemptions of available for sale securities	1,841,069	1,122,680	1,841,217
Purchases of investment securities	0	(4,468)	(32,972)
Purchases of available for sale securities	(5,245,256)	(1,955,172)	(2,845,557)
Proceeds from sales of available for sale securities	1,211,718	745,643	1,309,215
Change in amount receivable on unsettled available for sale securities transactions	25,410	38,347	(68,792)
Loans originated, net of principal collected	(44,414)	(1,553,033)	(78,232)
Net payments on derivative asset contracts	33,566	(114,417)	479,409
Acquisitions, net of cash acquired	0	(175,755)	0
Proceeds from disposition of assets	178,681	308,762	274,029
Purchases of assets	(384,639)	(345,082)	(250,783)
Net cash provided by (used in) investing activities	(2,323,737)	(1,807,631)	739,556
Cash Flows From Financing Activities: [Abstract]
Net change in demand deposits, transaction deposits and savings accounts	2,252,936	(13,870)	(563,406)
Net change in time deposits	104,288	(73,089)	(123,384)
Net change in other borrowed funds	1,110,970	1,295,484	(10,909)
Change in amount due on unsettled security purchases	(41,651)	(41,319)	144,690
Issuance of common and treasury stock, net	(7)	(88)	4,368
Net change in derivative margin accounts	(207,122)	85,466	(17,726)
Net payments or proceeds on derivative liability contracts	(33,622)	114,076	(485,119)
Repurchase of common stock	(129,483)	(53,465)	(7,403)
Dividends paid	(143,496)	(127,188)	(116,041)
Net cash provided by (used in) financing activities	2,912,813	1,186,007	(1,174,930)
Net increase (decrease) in cash and cash equivalents	115,397	(1,173,630)	(220,443)
Cash and cash equivalents at beginning of period	1,143,424	2,317,054	2,537,497
Cash and cash equivalents at end of period	1,258,821	1,143,424	2,317,054
Supplemental Cash Flow Information: [Abstract]
Cash paid for interest	417,070	243,121	127,513
Cash paid for taxes	87,361	92,291	121,697
Net loans and bank premises transferred to repossessed real estate and other assets	10,665	9,880	7,367
Increase in U.S. government guaranteed loans eligible for repurchase	91,634	100,238	148,107
Increase in receivables from conveyance of GNMA OREO	28,669	38,216	40,528
Right-of-use assets obtained in exchange for operating lease liabilities	$ 62,755	$ 0	$ 0