Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Cash Flows From Operating Activities: [Abstract]
Net income	$ 248,045	$ 220,502
Adjustments to reconcile net income to net cash used in operating activities:
Provision for credit losses	13,000	(5,000)
Change in fair value of mortgage servicing rights due to market changes	50,221	(22,929)
Change in the fair value of mortgage servicing rights due to principal payments	15,664	16,797
Net unrealized losses (gains) from derivative contracts	(17,095)	6,674
Share-based compensation	8,149	1,881
Depreciation and amortization	45,926	27,459
Net amortization of discounts and premiums	(10,913)	12,855
Net losses (gains) on financial instruments and other losses (gains), net	564	4,530
Net gain on mortgage loans held for sale	(16,735)	(19,314)
Mortgage loans originated for sale	(1,240,368)	(1,438,868)
Proceeds from sale of mortgage loans held for sale	1,215,756	1,456,312
Capitalized mortgage servicing rights	(14,939)	(19,720)
Change in trading and fair value option securities	(799,241)	(1,174,526)
Change in receivables	(228,973)	(335,369)
Change in other assets	(4,965)	1,737
Change in accrued interest, taxes and expense	(41,866)	(4,327)
Change in other liabilities	100,731	334,765
Net cash used in operating activities	(677,039)	(936,541)
Cash Flows From Investing Activities: [Abstract]
Proceeds from maturities or redemptions of investment securities	26,513	71,722
Proceeds from maturities or redemptions of available for sale securities	704,542	819,596
Purchases of investment securities	0	(3,968)
Purchases of available for sale securities	(2,510,271)	(1,020,018)
Proceeds from sales of available for sale securities	367,357	187,533
Change in amount receivable on unsettled available for sale securities transactions	(28,580)	38,075
Loans originated, net of principal collected	(569,075)	(847,351)
Net payments on derivative asset contracts	(10,838)	(70,987)
Acquisitions, net of cash acquired	0	(13,870)
Proceeds from disposition of assets	116,163	97,027
Purchases of assets	(250,911)	(121,889)
Net cash used in investing activities	(2,155,100)	(864,130)
Cash Flows From Financing Activities: [Abstract]
Net change in demand deposits, transaction deposits and savings accounts	(73,200)	78,643
Net change in time deposits	114,377	29,316
Net change in other borrowed funds	2,968,697	1,057,118
Net proceeds on derivative liability contracts	6,140	64,144
Net change in derivative margin accounts	(152,533)	(118,628)
Change in amount due on unsettled available for sale securities transactions	313,736	(100,847)
Issuance of common and treasury stock, net	(525)	(444)
Repurchase of common stock	(80,702)	(8,408)
Dividends paid	(71,784)	(58,477)
Net cash provided by financing activities	3,024,206	942,417
Net increase (decrease) in cash and cash equivalents	192,067	(858,254)
Cash and cash equivalents at beginning of period	1,143,424	2,317,054
Cash and cash equivalents at end of period	1,335,491	1,458,800
Supplemental Cash Flow Information: [Abstract]
Cash paid for interest	203,513	100,532
Cash paid for taxes	54,722	29,623
Net loans and bank premises transferred to repossessed real estate and other assets	2,606	3,886
Residential mortgage loans guaranteed by U.S. government agencies that became eligible for repurchase during the period	44,258	42,493
Conveyance of other real estate owned guaranteed by U.S. government agencies	15,484	23,845
Right-of-use assets obtained in exchange for operating lease liabilities	$ 12,754	$ 0