Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Cash Flows From Operating Activities: [Abstract]
Net income	$ 110,265	$ 105,347
Adjustments to reconcile net income to net cash used in operating activities:
Provision for credit losses	8,000	(5,000)
Change in fair value of mortgage servicing rights due to market changes	20,666	(21,206)
Change in the fair value of mortgage servicing rights due to principal payments	6,583	7,995
Net unrealized losses (gains) from derivative contracts	695	2,222
Share-based compensation	5,414	3,073
Depreciation and amortization	19,412	13,561
Net amortization of securities discounts and premiums	4,339	6,555
Net losses (gains) on financial instruments and other losses (gains), net	1,872	5,593
Net gain on mortgage loans held for sale	(5,640)	(7,549)
Mortgage loans originated for sale	(510,527)	(664,958)
Proceeds from sale of mortgage loans held for sale	507,459	670,598
Capitalized mortgage servicing rights	(6,188)	(8,900)
Change in trading and fair value option securities	(608,232)	(588,588)
Change in receivables	(682,957)	(33,631)
Change in other assets	(5,074)	(4,349)
Change in accrued interest, taxes and expense	(18,220)	(8,749)
Change in other liabilities	46,147	379,649
Net cash used in operating activities	(1,105,986)	(148,337)
Cash Flows From Investing Activities: [Abstract]
Proceeds from maturities or redemptions of investment securities	23,227	44,031
Proceeds from maturities or redemptions of available for sale securities	337,822	412,391
Purchases of available for sale securities	663,193	518,361
Proceeds from sales of available for sale securities	245,259	44,790
Change in amount receivable on unsettled available for sale securities transactions	31,618	72,342
Loans originated, net of principal collected	(97,656)	(180,381)
Net payments on derivative asset contracts	(33,781)	(40,537)
Proceeds from disposition of assets	70,379	44,620
Purchases of assets	(116,692)	(59,788)
Net cash used in investing activities	(203,017)	(180,893)
Cash Flows From Financing Activities: [Abstract]
Net change in demand deposits, transaction deposits and savings accounts	(16,970)	76,057
Net change in time deposits	84,828	67,838
Net change in other borrowed funds	1,614,995	544,157
Net proceeds on derivative liability contracts	36,250	41,486
Net change in derivative margin accounts	(150,722)	(24,490)
Change in amount due on unsettled available for sale securities transactions	(22,923)	(56,774)
Issuance of common and treasury stock, net	(549)	102
Repurchase of common stock	(60,577)	(7,584)
Dividends paid	(36,052)	(29,183)
Net cash provided by financing activities	1,448,280	611,609
Net increase in cash and cash equivalents	139,277	282,379
Cash and cash equivalents at beginning of period	1,143,424	2,317,054
Cash and cash equivalents at end of period	1,282,701	2,599,433
Supplemental Cash Flow Information: [Abstract]
Cash paid for interest	94,660	47,165
Cash paid for taxes	898	1,548
Net loans and bank premises transferred to repossessed real estate and other assets	1,032	2,156
Residential mortgage loans guaranteed by U.S. government agencies that became eligible for repurchase during the period	22,970	19,332
Conveyance of other real estate owned guaranteed by U.S. government agencies	$ 8,404	$ 11,817