Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Operating Activities
Net income	$ 226,082	$ 195,249	$ 159,383
Adjustments to reconcile net income to net cash provided by operating activities:
Provision for loan losses	19,010	33,831	69,598
Depreciation, amortization, and accretion, net	56,741	54,952	59,310
Deferred income tax expense	121,904	102,020	90,415
Decrease (increase) in trading account assets	8,766	(7,750)	4,989
Originations of mortgage loans held for sale	(790,625)	(766,815)	(841,542)
Proceeds from sales of mortgage loans held for sale	807,906	761,979	1,008,501
Gain on sales of mortgage loans held for sale, net	(14,966)	(12,357)	(13,649)
Decrease in other assets	7,799	2,258	45,435
Decrease in other liabilities	(24,906)	(8,990)	(11,284)
Investment securities gains, net	(2,769)	(1,331)	(2,945)
Losses and write-downs on other real estate, net	17,619	22,085	25,508
Losses and write-downs on other assets held for sale, net	892	7,643	3,917
Loss on early extinguishment of debt	1,533	0	0
Share-based compensation expense	12,556	10,233	7,465
Gain on sale of Memphis branches, net	0	(5,789)	0
Net cash provided by operating activities	447,542	387,218	605,101
Investing Activities
Net cash (used) received in dispositions/acquisitions	0	(90,571)	56,328
Net (increase) decrease in interest earning deposits with banks	(5,577)	12,515	(883)
Net decrease in federal funds sold and securities purchased under resale agreements	3,291	7,864	32,542
Net (increase) decrease in interest bearing funds with Federal Reserve Bank	(108,525)	(76,834)	853,862
Proceeds from maturities and principal collections of investment securities available for sale	693,608	568,918	711,134
Proceeds from sales of investment securities available for sale	347,954	20,815	407,718
Purchases of investment securities available for sale	(1,634,531)	(378,919)	(1,434,322)
Proceeds from sales of loans and principal repayments on other loans held for sale	28,762	65,205	160,444
Proceeds from sale of other real estate	47,137	63,768	100,802
Net increase in loans	(1,411,050)	(1,326,596)	(889,026)
Purchases of BOLI policies	(45,000)	0	0
Net increase in premises and equipment	(28,381)	(38,680)	(28,470)
Proceeds from sale of other assets held for sale	3,039	5,741	2,285
Net cash used in investing activities	(2,109,273)	(1,166,774)	(27,586)
Financing Activities
Net increase (decrease) in demand and savings deposits	2,274,949	562,669	(114,738)
Net (decrease) increase in certificates of deposit	(565,315)	283,543	(122,343)
Net increase (decrease) in federal funds purchased and securities sold under repurchase agreements	50,109	(21,216)	(53,111)
Repayments on long-term debt	(823,899)	(400,781)	(307,571)
Proceeds from issuance of long-term debt	871,644	510,000	617,500
Dividends paid to common shareholders	(55,354)	(42,805)	(36,427)
Stock options exercised	5,643	3,048	1,044
Proceeds from issuance of Series C Preferred Stock, net of issuance costs	0	0	125,862
Redemption of Series A Preferred Stock	0	0	(967,870)
Proceeds from issuance of common stock, net of issuance costs	0	0	175,174
Repurchases and agreements to repurchase shares of common stock	(199,221)	(88,113)	0
Restricted stock activity	(4,984)	(692)	(3,564)
Net cash provided by (used in) financing activities	1,543,334	795,415	(722,515)
(Decrease) increase in cash and cash equivalents	(118,397)	15,859	(145,000)
Cash and cash equivalents at beginning of year	485,489	469,630	614,630
Cash and cash equivalents at end of year	367,092	485,489	469,630
Supplemental Cash Flow Information
Income tax payments, net	10,514	5,971	2,577
Interest paid	115,795	109,549	121,291
Non-cash Activities:
Mortgage loans held for sale transferred to loans at fair value	659	334	14,714
Loans foreclosed and transferred to other real estate	26,313	58,556	85,422
Premises and equipment transferred to other assets held for sale at fair value	2,340	16,613	6,254
Securities purchased during the period but settled after period-end	0	25,938	0
Dispositions/Acquisitions:
Fair value of non-cash assets (sold) acquired	0	(100,982)	536
Fair value of liabilities (sold) assumed	0	(191,553)	56,864
Series C Preferred Stock [Member]
Financing Activities
Dividends paid to preferred shareholders	(10,238)	(10,238)	(2,730)
Series A Preferred Stock [Member]
Financing Activities
Dividends paid to preferred shareholders	$ 0	$ 0	$ (33,741)