Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Operating Activities:
Net income	$ 331,151	$ 443,599	$ 454,918
Adjustments to reconcile net income to net cash from operating activities:
Credit loss expense	241,230	33,759	21,685
Deferred tax expense (benefit)	(15,832)	7,614	52,923
Accretion of loan discounts	(15,692)	(15,197)	(14,341)
Securities premium amortization (discount accretion), net	123,785	115,558	100,528
Net (gain) loss on securities transactions	(108,989)	(293)	156
Depreciation and amortization	64,370	54,091	50,172
Net (gain) loss on sale/write-down of assets/foreclosed assets	524	(5,712)	(5,272)
Stock-based compensation	13,918	15,946	13,943
Net tax benefit from stock-based compensation	852	2,447	3,865
Earnings on life insurance policies	(3,731)	(3,683)	(3,380)
Net change in:
Trading account securities	(158)	(212)	(2,658)
Lease right-of-use asset	23,933	20,124	0
Accrued interest receivable and other assets	(158,264)	(15,570)	(85,898)
Accrued interest payable and other liabilities	27,146	(18,381)	(24,253)
Net cash provided by (used in) operating activities	524,243	634,090	562,388
Investing Activities:
Securities held to maturity: Purchases	(1,500)	(649,326)	(1,500)
Securities held to maturity: Maturities, calls and principal repayments	63,577	81,762	300,632
Securities available for sale:
Purchases	(20,841,622)	(23,306,694)	(18,191,057)
Sales	1,162,352	18,660,147	16,806,062
Maturities, calls and principal repayments	20,893,464	4,694,927	221,906
Proceeds from sale of loans	37,535	24,036	21,318
Net change in loans	(2,856,395)	(693,587)	(1,008,789)
Benefits received on life insurance policies	903	0	384
Proceeds from sales of premises and equipment	5,988	8,038	13,628
Purchases of premises and equipment	(95,422)	(206,716)	(79,270)
Proceeds from sales of repossessed properties	73	663	3,366
Net cash provided by (used in) investing activities	(1,631,047)	(1,386,750)	(1,913,320)
Financing Activities:
Net change in deposits	7,376,197	490,360	276,815
Net change in short-term borrowings	421,655	327,794	219,724
Proceeds from Federal Home Loan Bank advances	1,250,000	0	0
Principal payments on Federal Home Loan Bank advances	(1,250,000)	0	0
Redemption of Series A preferred stock	(150,000)	0	0
Proceeds from issuance of Series B preferred stock	145,452	0	0
Proceeds from stock option exercises	12,557	20,770	31,647
Purchase of treasury stock	(15,785)	(68,793)	(101,010)
Cash dividends paid on preferred stock	(2,016)	(8,063)	(8,063)
Cash dividends paid on common stock	(180,584)	(177,006)	(165,449)
Net cash provided by (used in) financing activities	7,607,476	585,062	253,664
Net change in cash and cash equivalents	6,500,672	(167,598)	(1,097,268)
Cash and cash equivalents at beginning of year	3,788,181	3,955,779	5,053,047
Cash and cash equivalents at end of year	$ 10,288,853	$ 3,788,181	$ 3,955,779