Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Operating Activities
Net income	$ 246,784	$ 226,082	$ 195,249
Adjustments to reconcile net income to net cash provided by operating activities:
Provision for loan losses	28,000	19,010	33,831
Depreciation, amortization, and accretion, net	58,228	56,741	54,952
Deferred income tax expense	128,837	121,904	102,020
(Increase) decrease in trading account assets	(2,327)	8,766	(7,750)
Originations of mortgage loans held for sale	(705,394)	(790,625)	(766,815)
Proceeds from sales of mortgage loans held for sale	724,712	807,906	761,979
Gain on sales of mortgage loans held for sale, net	(13,780)	(14,966)	(12,357)
(Increase) decrease in other assets	(23,568)	7,799	2,258
Decrease in other liabilities	(4,239)	(24,906)	(8,990)
Investment securities gains, net	(6,011)	(2,769)	(1,331)
Losses and write-downs on other real estate, net	10,174	17,619	22,085
Losses and write-downs on other assets held for sale, net	8,001	892	7,643
Loss on early extinguishment of debt, net	4,735	1,533	0
Share-based compensation expense	13,615	12,556	10,233
Gain on sale of Memphis branches, net	0	0	(5,789)
Net cash provided by operating activities	467,767	447,542	387,218
Investing Activities
Net cash received (used) in acquisitions/dispositions	6,146	0	(90,571)
Net (increase) decrease in interest earning deposits with banks	(1,335)	(5,577)	12,515
Net decrease in federal funds sold and securities purchased under resale agreements	11,759	3,291	7,864
Net decrease (increase) in interest bearing funds with Federal Reserve Bank	302,797	(108,525)	(76,834)
Proceeds from maturities and principal collections of investment securities available for sale	894,123	693,608	568,918
Proceeds from sales of investment securities available for sale	968,606	347,954	20,815
Purchases of investment securities available for sale	(2,051,283)	(1,634,531)	(378,919)
Proceeds from sales of loans	15,046	28,762	65,205
Proceeds from sale of other real estate	30,762	47,137	63,768
Net increase in loans	(1,129,422)	(1,411,050)	(1,326,596)
Purchase of Federal Reserve Bank capital stock	(97,293)	0	0
Purchase of bank-owned life insurance policies	(34,256)	(45,000)	0
Net increase in premises and equipment	(34,317)	(28,381)	(38,680)
Proceeds from sale of other assets held for sale	13,072	3,039	5,741
Net cash used in investing activities	(1,105,595)	(2,109,273)	(1,166,774)
Financing Activities
Net increase in demand and savings deposits	1,512,451	2,274,949	562,669
Net (decrease) increase in certificates of deposit	(107,893)	(565,315)	283,543
Net (decrease) increase in federal funds purchased and securities sold under repurchase agreements	(17,326)	50,109	(21,216)
Repayments on long-term debt	(2,263,688)	(823,899)	(400,781)
Proceeds from issuance of long-term debt	1,875,000	871,644	510,000
Dividends paid to common shareholders	(59,425)	(55,354)	(42,805)
Dividends paid to preferred shareholders	(10,238)	(10,238)	(10,238)
Stock options exercised	5,155	5,643	3,048
Repurchases and agreements to repurchase shares of common stock	(263,084)	(199,221)	(88,113)
Restricted stock activity	(5,041)	(4,984)	(692)
Net cash provided by financing activities	665,911	1,543,334	795,415
Increase (decrease) in cash and cash equivalents	28,083	(118,397)	15,859
Cash and cash equivalents at beginning of year	367,092	485,489	469,630
Cash and cash equivalents at end of year	395,175	367,092	485,489
Supplemental Cash Flow Information
Income tax payments, net	9,340	10,514	5,971
Interest paid	123,560	115,795	109,549
Non-cash Activities:
Mortgage loans held for sale transferred to loans at fair value	313	659	334
Loans foreclosed and transferred to other real estate	16,214	26,313	58,556
Premises and equipment transferred to other properties held for sale	25,231	2,340	16,613
Investment securities available for sale transferred to trading account assets at fair value	1,890	0	0
Securities purchased during the period but settled after period-end	0	0	25,938
Dispositions/Acquisitions:
Fair value of non-cash assets acquired (sold)	408,054	0	(100,982)
Fair value of liabilities assumed (sold)	387,608	0	(191,553)
Fair value of common stock issued	$ 26,592	$ 0	$ 0