Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
Cash Flows From Operating Activities: [Abstract]
Net income	$ 177,530	$ 107,260
Adjustments to reconcile net income to net cash provided by operating activities:
Provision for credit losses	0	55,000
Change in fair value of mortgage servicing rights due to market changes	5,087	44,271
Change in the fair value of mortgage servicing rights due to loan runoff	16,261	17,942
Net unrealized gains from derivative contracts	(5,928)	(15,459)
Share-based compensation	8,983	5,730
Depreciation and amortization	25,864	23,532
Net amortization of securities discounts and premiums	15,377	21,814
Net realized gains on financial instruments and other net gains	(4,351)	(9,787)
Net gain on mortgage loans held for sale	(25,229)	(37,151)
Mortgage loans originated for sale	(1,613,997)	(3,062,859)
Proceeds from sale of mortgage loans held for sale	1,651,018	2,981,973
Capitalized mortgage servicing rights	(19,514)	(34,355)
Change in trading and fair value option securities	(472,682)	90,484
Change in receivables	479,774	(9,698)
Change in other assets	(17,548)	(4,740)
Change in accrued interest, taxes and expense	(19,703)	20,299
Change in other liabilities	27,420	(8,854)
Net cash provided by operating activities	228,362	185,402
Cash Flows From Investing Activities: [Abstract]
Proceeds from maturities or redemptions of investment securities	71,654	52,463
Proceeds from maturities or redemptions of available for sale securities	899,096	721,432
Purchases of investment securities	(18,802)	(18,599)
Purchases of available for sale securities	(1,242,070)	(1,155,261)
Proceeds from sales of available for sale securities	700,412	795,140
Change in amount receivable on unsettled securities transactions	(25,989)	(102,627)
Loans originated, net of principal collected	(159,924)	(481,085)
Net payments on derivative asset contracts	420,996	(204,041)
Acquisitions, net of cash acquired	0	(7,700)
Proceeds from disposition of assets	127,699	78,629
Purchases of assets	(106,362)	(107,241)
Net cash provided by investing activities	666,710	(428,890)
Cash Flows From Financing Activities: [Abstract]
Net change in demand deposits, transaction deposits and savings accounts	(405,943)	(169,354)
Net change in time deposits	(25,678)	(159,003)
Net change in other borrowed funds	64,833	259,359
Issuance of subordinated debentures	0	145,390
Net proceeds on derivative liability contracts	(422,016)	196,225
Net change in derivative margin accounts	27,327	(188,823)
Change in amount due on unsettled security transactions	26,128	(5,140)
Issuance of common and treasury stock, net	588	2,276
Repurchase of common stock	0	17,770
Dividends paid	(57,390)	(56,720)
Net cash provided by (used in) financing activities	(792,151)	6,440
Net increase (decrease) in cash and cash equivalents	102,921	(237,048)
Cash and cash equivalents at beginning of period	2,537,497	2,643,599
Cash and cash equivalents at end of period	2,640,418	2,406,551
Supplemental Cash Flow Information: [Abstract]
Cash paid for interest	54,881	40,213
Cash paid for taxes	60,654	14,671
Net loans and bank premises transferred to repossessed real estate and other assets	2,049	5,372
Residential mortgage loans guaranteed by U.S. government agencies that became eligible for repurchase during the period	59,171	49,325
Conveyance of other real estate owned guaranteed by U.S. government agencies	$ 22,602	$ 29,512