Consolidated Statements of Income - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Interest income:
Loans, including fees	$ 877,384	$ 862,916	$ 866,358
Investment securities available for sale	59,154	57,832	52,567
Trading account assets	303	456	548
Mortgage loans held for sale	2,546	2,304	4,441
Federal Reserve Bank balances	3,144	2,081	3,222
Other earning assets	3,431	3,103	1,878
Total interest income	945,962	928,692	929,014
Interest expense:
Deposits	65,534	55,179	64,392
Federal funds purchased and securities sold under repurchase agreements	168	220	324
Long-term debt	52,942	54,009	54,106
Total interest expense	118,644	109,408	118,822
Net interest income	827,318	819,284	810,192
Provision for loan losses	19,010	33,831	69,598
Net interest income after provision for loan losses	808,308	785,453	740,594
Non-interest income:
Service charges on deposit accounts	80,142	78,897	77,789
Fiduciary and asset management fees	45,928	45,226	43,450
Brokerage revenue	27,855	27,088	27,538
Mortgage banking income	24,096	18,354	22,482
Bankcard fees	33,172	32,931	30,641
Investment securities gains, net	2,769	1,331	2,945
Other fee income	21,170	19,130	22,567
Gain on sale of Memphis branches, net	0	5,789	0
Other non-interest income	32,788	33,358	26,159
Total non-interest income	267,920	262,104	253,571
Non-interest expense:
Salaries and other personnel expense	380,918	371,904	368,152
Net occupancy and equipment expense	107,466	105,806	103,339
Third-party processing expense	42,851	40,042	40,135
FDIC insurance and other regulatory fees	27,091	33,485	32,456
Professional fees	26,646	26,440	38,776
Advertising expense	15,477	24,037	8,971
Foreclosed real estate expense, net	22,803	25,321	33,864
Visa indemnification charges	1,464	3,041	1,600
Loss on early extinguishment of debt	1,533	0	0
Restructuring charges	36	20,585	11,064
Other operating expenses	91,370	94,337	103,180
Total non-interest expense	717,655	744,998	741,537
Income before income taxes	358,573	302,559	252,628
Income tax expense	132,491	107,310	93,245
Net income	226,082	195,249	159,383
Dividends and accretion of discount on preferred stock	10,238	10,238	40,830
Net income available to common shareholders	$ 215,844	$ 185,011	$ 118,553
Net income per common share, basic (per share)	$ 1.63	$ 1.34	$ 0.93
Net income per common share, diluted (per share)	$ 1.62	$ 1.33	$ 0.88
Weighted average common shares outstanding, basic	132,423	138,495	127,495
Weighted average common shares outstanding, diluted	133,201	139,154	134,226