Consolidated Statements Of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
OPERATING ACTIVITIES:
Net income	$ 319,900	$ 276,854	$ 266,975
Adjustments to reconcile net income to net cash provided by operating activities:
Provision for loan losses	45,244	36,318	28,727
Provision for depreciation and amortization	39,732	40,929	42,803
Amortization of investment security premiums, net	35,423	31,493	32,618
Deferred income tax (benefit) expense	13,617	(2,059)	7,432
Investment securities (gains) losses, net	(25,051)	53	(6,320)
Net gains on sales of loans held for sale	(8,008)	(5,850)	(3,076)
Proceeds from sales of loans held for sale	215,373	160,875	97,813
Origination Of Loans Held For Sale	(216,064)	(163,469)	(103,199)
Net (increase) decrease in trading securities	7,585	73,780	(86,045)
Stock-based compensation	12,105	11,525	10,147
(Increase) decrease in interest receivable	(4,459)	(3,642)	(4,992)
Decrease in interest payable	38	1,107	336
Increase (decrease) in income taxes payable	(27,685)	4,509	11,733
Donation of securities	32,036	0	0
Other changes, net	(6,560)	(26,666)	(3,757)
Net cash provided by (used in) operating activities	433,226	435,757	291,195
INVESTING ACTIVITIES
Proceeds from sales of available for sale securities	792,380	24,380	689,031
Proceeds from maturities/pay downs of available for sale securities	1,899,640	2,032,397	2,515,113
Purchases of available for sale securities	(1,853,817)	(1,988,101)	(3,542,537)
Net (increase) decrease in loans	(614,849)	(1,009,523)	(1,005,657)
Repayments of long-term securities purchased under agreements to resell	(75,000)	(250,000)	0
Proceeds from Securities Purchased under Agreements to Resell	100,000	400,000	175,000
Purchases of land, buildings and equipment	(30,824)	(24,478)	(31,897)
Sales of land, buildings and equipment	3,190	10,112	5,545
Net cash provided by (used in) investing activities	220,720	(805,213)	(1,195,402)
FINANCING ACTIVITIES
Net increase (decrease) in non-interest bearing, savings, interest checking and money market deposits	(15,036)	782,846	545,147
Net increase (decrease) in time open and C.D.’s	(474,044)	243,199	(124,509)
Net increase (decrease) in short-term federal funds purchased and securities sold under agreements to repurchase	(216,767)	(239,647)	101,034
Repayment of other long-term borrowings	(100,291)	(1,769)	(240)
Purchases of treasury stock	(17,771)	(39,381)	(23,176)
Accelerated stock repurchase agreement net outflow	0	0	(100,000)
Issuance of stock under equity compensation plans	(8)	(6)
Proceeds from stock options exercised			1,914
Cash dividends paid on common stock	(91,619)	(87,070)	(84,961)
Cash dividends paid on preferred stock	(9,000)	(9,000)	(9,000)
Net cash provided by (used in) financing activities	(924,536)	649,172	306,209
Increase (decrease) in cash and cash equivalents	(270,590)	279,716	(597,998)
Cash and cash equivalents at beginning of year	782,435	502,719	1,100,717
Cash and cash equivalents at end of year	511,845	782,435	502,719
Supplemental Cash Flow Information:
Income tax payments, net	120,744	119,596	95,341
Interest paid on deposits and borrowings	43,690	31,896	27,760
Loans transferred to foreclosed real estate	2,063	1,122	3,778
Accelerated Share Repurchases, Settlement (Payment) or Receipt	0	0	60,000
Transfer of Portfolio Loans and Leases to Held-for-sale	$ 0	$ 42,688	$ 0