Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Operating Activities:
Net income	$ 443,599	$ 454,918	$ 364,149
Adjustments to reconcile net income to net cash from operating activities:
Provision for loan losses	33,759	21,613	35,460
Deferred tax expense (benefit)	7,614	52,923	(14,493)
Accretion of loan discounts	(15,197)	(14,341)	(16,062)
Securities premium amortization (discount accretion), net	115,558	100,528	89,933
Net (gain) loss on securities transactions	(293)	156	4,941
Depreciation and amortization	54,091	50,172	47,812
Net (gain) loss on sale/write-down of assets/foreclosed assets	(5,712)	(5,272)	(4,697)
Stock-based compensation	15,946	13,943	13,013
Net tax benefit from stock-based compensation	2,447	3,865	9,062
Earnings on life insurance policies	(3,683)	(3,380)	(3,190)
Net change in:
Trading account securities	(212)	(2,658)	(3,842)
Lease right-of-use asset	20,124	0	0
Accrued interest receivable and other assets	(15,570)	(85,898)	(55,179)
Accrued interest payable and other liabilities	(18,381)	(24,181)	71,172
Net cash provided by (used in) operating activities	634,090	562,388	538,079
Investing Activities:
Securities held to maturity: Purchases	(649,326)	(1,500)	0
Securities held to maturity: Maturities, calls and principal repayments	81,762	300,632	783,176
Securities available for sale:
Purchases	(23,306,694)	(18,191,057)	(13,529,192)
Sales	18,660,147	16,806,062	11,963,359
Maturities, calls and principal repayments	4,694,927	221,906	1,328,143
Proceeds from sale of loans	24,036	21,318	0
Net change in loans	(693,587)	(1,008,789)	(1,187,631)
Benefits received on life insurance policies	0	384	597
Proceeds from sales of premises and equipment	8,038	13,628	4,525
Purchases of premises and equipment	(206,716)	(79,270)	(34,089)
Proceeds from sales of repossessed properties	663	3,366	517
Net cash provided by (used in) investing activities	(1,386,750)	(1,913,320)	(670,595)
Financing Activities:
Net change in deposits	490,360	276,815	1,060,814
Net change in short-term borrowings	327,794	219,724	170,832
Proceeds from issuance of subordinated notes	0	0	98,434
Principal payments on subordinated notes	0	0	(100,000)
Proceeds from stock option exercises	20,770	31,647	67,746
Purchase of treasury stock	(68,793)	(101,010)	(101,473)
Cash dividends paid on preferred stock	(8,063)	(8,063)	(8,063)
Cash dividends paid on common stock	(177,006)	(165,449)	(144,172)
Net cash provided by (used in) financing activities	585,062	253,664	1,044,118
Net change in cash and cash equivalents	(167,598)	(1,097,268)	911,602
Cash and cash equivalents at beginning of year	3,955,779	5,053,047	4,141,445
Cash and cash equivalents at end of year	$ 3,788,181	$ 3,955,779	$ 5,053,047