Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Operating Activities:
Net income	$ 454,918	$ 364,149	$ 304,261
Adjustments to reconcile net income to net cash from operating activities:
Provision for loan losses	21,613	35,460	51,673
Deferred tax expense (benefit)	52,923	(14,493)	(11,598)
Accretion of loan discounts	(14,341)	(16,062)	(15,582)
Securities premium amortization (discount accretion), net	100,528	89,933	79,705
Net (gain) loss on securities transactions	156	4,941	(14,975)
Depreciation and amortization	50,172	47,812	48,177
Net (gain) loss on sale/write-down of assets/foreclosed assets	(5,272)	(4,697)	(3,618)
Stock-based compensation	13,943	13,013	11,799
Net tax benefit from stock-based compensation	3,865	9,062	5,063
Earnings on life insurance policies	(3,380)	(3,190)	(3,599)
Net change in:
Trading account securities	(2,658)	(3,842)	(124)
Accrued interest receivable and other assets	(85,898)	(55,179)	(7,395)
Accrued interest payable and other liabilities	(24,181)	71,172	(5,945)
Net cash from operating activities	562,388	538,079	437,842
Investing Activities:
Securities held to maturity: Purchases	(1,500)	0	0
Securities held to maturity: Sales	0	0	136,719
Securities held to maturity: Maturities, calls and principal repayments	300,632	783,176	228,641
Securities available for sale:
Purchases	(18,191,057)	(13,529,192)	(16,419,833)
Sales	16,806,062	11,963,359	14,847,380
Maturities, calls and principal repayments	221,906	1,328,143	335,750
Proceeds from sale of loans	21,318	0	30,470
Net change in loans	(1,008,789)	(1,187,631)	(538,989)
Net cash (paid) received in acquisitions	0	0	(492)
Benefits received on life insurance policies	384	597	906
Proceeds from sales of premises and equipment	13,628	4,525	58,774
Purchases of premises and equipment	(79,270)	(34,089)	(53,648)
Proceeds from sales of repossessed properties	3,366	517	341
Net cash from investing activities	(1,913,320)	(670,595)	(1,373,981)
Financing Activities:
Net change in deposits	276,815	1,060,814	1,467,980
Net change in short-term borrowings	219,724	170,832	83,470
Proceeds from issuance of subordinated notes	0	98,434	0
Principal payments on subordinated notes	0	(100,000)	0
Proceeds from stock option exercises	31,647	67,746	78,866
Purchase of treasury stock	(101,010)	(101,473)	(1,290)
Cash dividends paid on preferred stock	(8,063)	(8,063)	(8,063)
Cash dividends paid on common stock	(165,449)	(144,172)	(134,902)
Net cash from financing activities	253,664	1,044,118	1,486,061
Net change in cash and cash equivalents	(1,097,268)	911,602	549,922
Cash and cash equivalents at beginning of year	5,053,047	4,141,445	3,591,523
Cash and cash equivalents at end of year	$ 3,955,779	$ 5,053,047	$ 4,141,445