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:
Net income	$ 395,043	$ 422,417	$ 466,201
Adjustments to reconcile net income to net cash provided by operating activities:
Provision for loan losses	7,105	18,256	37,242
Depreciation	27,096	32,323	32,803
Amortization of discounts and premiums, net	7,951	(3,891)	(4,555)
Amortization of core deposit intangibles			208
Net (gain) loss on securities	(7,725)	14	(29,924)
Gain on trading activity	(66)	(222)	(316)
Net loss (gain) on sales of loans	75	(111)	(87,301)
Net gain on sales of fixed assets	(7,402)
Stock-based compensation	32,048	36,260	36,029
Deferred tax expense	100,813	23,197	21,444
Changes in operating assets and liabilities:
(Increase) decrease in other assets	(55,825)	29,952	451,873
Increase (decrease) in other liabilities	10,571	(53,320)	23,329
Purchases of securities held for trading	(42,500)	(141,615)	(202,450)
Proceeds from sales of securities held for trading	42,566	141,837	202,766
Origination of loans held for sale			(1,674,123)
Proceeds from sales of loans originated for sale		35,258	2,053,484
Net cash provided by operating activities	509,750	540,355	1,326,710
CASH FLOWS FROM INVESTING ACTIVITIES:
Proceeds from repayment of securities held to maturity			175,375
Proceeds from repayment of securities available for sale	1,962,433	817,822	387,772
Proceeds from sales of securities held to maturity			547,925
Proceeds from sales of securities available for sale	361,311	278,539	453,878
Purchase of securities held to maturity			(13,030)
Purchase of securities available for sale	(2,503,248)	(3,288,204)	(1,163,043)
Redemption of Federal Home Loan Bank stock	135,906	120,220	90,909
Purchases of Federal Home Loan Bank stock	(138,878)	(160,991)	(103,794)
Purchases of (proceeds from) bank-owned life insurance, net	(138,119)	16,303
Proceeds from sales of loans	115,205	195,760	2,289,377
Purchases of loans	(864,299)
Other changes in loans, net	(998,515)	(1,990,068)	(1,575,846)
Proceeds from sales (purchases) of premises and equipment, net	9,297	(9,847)	(27,783)
Net cash provided by (used in) investing activities	(2,058,907)	(4,020,466)	1,061,740
CASH FLOWS FROM FINANCING ACTIVITIES:
Net increase in deposits	892,702	1,662,267	214,260
Net increase (decrease) in short-term borrowed funds	1,100,000		(460,000)
Proceeds from long-term borrowed funds	4,785,812	5,667,268	3,000,000
Repayments of long-term borrowed funds	(5,537,000)	(4,373,500)	(3,300,000)
Net proceeds from issuance of preferred stock			502,840
Cash dividends paid on common stock	(317,394)	(333,061)	(332,147)
Cash dividends paid on preferred stock	(32,828)	(32,828)	(24,621)
Treasury stock repurchased	(67,125)	(160,767)
Payments relating to treasury shares received for restricted stock award tax payments	(8,095)	(2,482)	(18,463)
Net cash provided by (used in) financing activities	816,072	2,426,897	(418,131)
Net (decrease) increase in cash, cash equivalents, and restricted cash	(733,085)	(1,053,214)	1,970,319
Cash, cash equivalents, and restricted cash at beginning of year	1,474,955	2,528,169	557,850
Cash, cash equivalents, and restricted cash at end of year	741,870	1,474,955	2,528,169
Supplemental information:
Cash paid for interest	813,161	645,588	447,476
Cash paid for income taxes	75,680	44,123	217,682
Non-cash investing and financing activities:
Transfers to repossessed assets from loans	4,689	5,631	9,973
Operating lease liabilities arising from obtaining right-of-use assets as of January 1, 2019	324,360
Securitization of residential mortgage loans to mortgage-backed securities available for sale	93,531
Transfer of loans from held for investment to held for sale	115,280	195,649	1,910,121
Disposition of premises and equipment	1,245
Shares issued for restricted stock awards	$ 16,501	$ 8,879	11,028
Securities transferred from held to maturity to available for sale			$ 3,040,305