Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Cash Flows From Operating Activities: [Abstract]
Net income	$ 435,071	$ 500,685	$ 446,424
Adjustments to reconcile net income to net cash provided by (used in) operating activities: [Abstract]
Provision for credit losses	222,592	44,000	8,000
Change in fair value of mortgage servicing rights due to market changes	79,524	53,517	(4,668)
Change in fair value of mortgage servicing rights due to principal payments	41,598	38,979	33,528
Net unrealized losses (gains) from derivative contracts	(59,253)	(25,936)	4,686
Share-based compensation	16,392	15,544	4,229
Depreciation and amortization	99,013	95,416	60,843
Net amortization of discounts and premiums	5,357	(16,984)	30,945
Net losses (gains) on financial instruments and other losses (gains), net	(15,949)	(583)	9,585
Net gain on mortgage loans held for sale	(114,545)	(40,402)	(35,705)
Mortgage loans originated for sale	(3,764,112)	(3,025,930)	(2,587,297)
Proceeds from sale of mortgage loans held for sale	3,817,475	3,035,600	2,691,144
Capitalized mortgage servicing rights	(31,209)	(35,128)	(35,247)
Change in trading and fair value option securities	(2,103,931)	(483,007)	(1,023,097)
Change in receivables	945,087	(740,868)	(38,346)
Change in other assets	1,739	18,955	27,507
Change in other liabilities	8,895	92,463	(144,537)
Net cash provided by (used in) operating activities	(416,256)	(473,679)	(552,006)
Cash Flows From Investing Activities: [Abstract]
Proceeds from maturities or redemptions of investment securities	46,992	60,128	124,864
Proceeds from maturities or redemptions of available for sale securities	2,695,067	1,841,069	1,122,680
Purchases of investment securities	0	0	(4,468)
Purchases of available for sale securities	(4,575,324)	(5,245,256)	(1,955,172)
Proceeds from sales of available for sale securities	384,507	1,211,718	745,643
Change in amount receivable on unsettled available for sale securities transactions	(6,357)	25,410	38,347
Loans originated, net of principal collected	(1,103,752)	(44,414)	(1,553,033)
Net payments on derivative asset contracts	(121,130)	33,566	(114,417)
Acquisitions, net of cash acquired	0	0	(175,755)
Net change in restricted equity securities	289,161	116,105	18,997
Proceeds from disposition of assets	73,135	62,576	289,765
Purchases of assets	(141,134)	(384,639)	(345,082)
Net cash provided by (used in) investing activities	(2,458,835)	(2,323,737)	(1,807,631)
Cash Flows From Financing Activities: [Abstract]
Net change in demand deposits, transaction deposits and savings accounts	8,773,433	2,252,936	(13,870)
Net change in time deposits	(250,721)	104,288	(73,089)
Net change in other borrowed funds	(5,091,026)	1,110,970	1,295,484
Change in amount due on unsettled security purchases	63,521	(41,651)	(41,319)
Issuance of common and treasury stock, net	(4,933)	(7)	(88)
Net change in derivative margin accounts	(600,218)	(207,122)	85,466
Net payments or proceeds on derivative liability contracts	127,054	(33,622)	114,076
Repurchase of common stock	(75,830)	(129,483)	(53,465)
Dividends paid	(144,437)	(143,496)	(127,188)
Net cash provided by (used in) financing activities	2,796,843	2,912,813	1,186,007
Net increase (decrease) in cash and cash equivalents	(78,248)	115,397	(1,173,630)
Cash and cash equivalents at beginning of period	1,258,821	1,143,424	2,317,054
Cash and cash equivalents at end of period	1,180,573	1,258,821	1,143,424
Supplemental Cash Flow Information: [Abstract]
Cash paid for interest	160,288	417,070	243,121
Cash paid for taxes	136,181	87,361	92,291
Net loans and bank premises transferred to repossessed real estate and other assets	85,323	10,665	9,880
Increase in U.S. government guaranteed loans eligible for repurchase	290,977	91,634	100,238
Increase in receivables from conveyance of GNMA OREO	11,322	28,669	38,216
Right-of-use assets obtained in exchange for operating lease liabilities	$ 16,177	$ 62,755	$ 0