Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating Activities:
Net income	$ 364,149	$ 304,261	$ 279,328
Adjustments to reconcile net income to net cash from operating activities:
Provision for loan losses	35,460	51,673	51,845
Deferred tax expense (benefit)	(14,493)	(11,598)	(19,059)
Accretion of loan discounts	(16,062)	(15,582)	(14,447)
Securities premium amortization (discount accretion), net	89,933	79,705	73,785
Net (gain) loss on securities transactions	4,941	(14,975)	(69)
Depreciation and amortization	47,812	48,177	42,138
Net (gain) loss on sale/write-down of assets/foreclosed assets	(4,697)	(3,618)	(1,765)
Stock-based compensation	13,013	11,799	12,737
Net tax benefit from stock-based compensation	9,062	5,063	1,434
Earnings on life insurance policies	(3,190)	(3,599)	(3,585)
Net change in:
Trading account securities	(3,842)	(124)	(1,153)
Accrued interest receivable and other assets	(55,179)	(7,395)	(13,038)
Accrued interest payable and other liabilities	71,172	(5,945)	(13,291)
Net cash from operating activities	538,079	437,842	394,860
Investing Activities:
Securities held to maturity: Purchases	0	0	(1,350)
Securities held to maturity: Sales	0	136,719	0
Securities held to maturity: Maturities, calls and principal repayments	783,176	228,641	209,425
Securities available for sale:
Purchases	(13,529,192)	(16,419,833)	(14,147,908)
Sales	11,963,359	14,847,380	12,683,169
Maturities, calls and principal repayments	1,328,143	335,750	658,199
Proceeds from sale of loans	0	30,470	0
Net change in loans	(1,187,631)	(538,989)	(500,990)
Net cash (paid) received in acquisitions	0	(492)	0
Benefits received on life insurance policies	597	906	444
Proceeds from sales of premises and equipment	4,525	58,774	2,538
Purchases of premises and equipment	(34,089)	(53,648)	(147,129)
Proceeds from sales of repossessed properties	517	341	4,682
Net cash from investing activities	(670,595)	(1,373,981)	(1,238,920)
Financing Activities:
Net change in deposits	1,060,814	1,467,980	207,665
Net change in short-term borrowings	170,832	83,470	90,403
Proceeds from issuance of subordinated notes	98,434	0	0
Principal payments on subordinated notes	(100,000)	0	0
Proceeds from stock option exercises	67,746	78,866	14,853
Purchase of treasury stock	(101,473)	(1,290)	(101,237)
Cash dividends paid on preferred stock	(8,063)	(8,063)	(8,063)
Cash dividends paid on common stock	(144,172)	(134,902)	(132,161)
Net cash from financing activities	1,044,118	1,486,061	71,460
Net change in cash and cash equivalents	911,602	549,922	(772,600)
Cash and cash equivalents at beginning of year	4,141,445	3,591,523	4,364,123
Cash and cash equivalents at end of year	$ 5,053,047	$ 4,141,445	$ 3,591,523