Loans and Allowance for Loan Losses - Allowance for loan losses by portfolio (Details) - USD ($) $ in Thousands		Mar. 31, 2016	Dec. 31, 2015	Mar. 31, 2015	Dec. 31, 2014
Ending balance of allowance attributable to loans:
Individually evaluated for impairment		$ 100,660	$ 71,217
Collectively evaluated for impairment		720,464	689,847
Purchased nonimpaired, covered		54	100
Purchased nonimpaired, total loans		223	269
Total allowance for loan losses, covered		1,147	1,440	$ 1,468	$ 2,808
Total allowance for loan losses, total loans		822,440	762,673	701,864	685,041
Ending balance of loans:
Individually evaluated for impairment		792,977	429,586
Collectively evaluated for impairment		60,813,886	60,374,619
Purchased nonimpaired loans, covered		111,925	117,869
Purchased nonimpaired loans, total loans		185,933	196,787
Covered loans		423,819	440,961
Total loans		62,104,690	61,324,084
Receivables acquired with deteriorated credit quality
Ending balance of allowance attributable to loans:
Purchased impaired		1,093	1,340
Ending balance of loans:
Purchased impaired		311,894	323,092
Commercial, Financial and Agricultural
Ending balance of allowance attributable to loans:
Individually evaluated for impairment		59,143	27,486
Collectively evaluated for impairment		408,326	374,458
Purchased nonimpaired		169	169
Total allowance for loan losses		467,638	402,113	323,397	299,482
Ending balance of loans:
Individually evaluated for impairment		561,381	163,201
Collectively evaluated for impairment		26,267,226	25,828,286
Purchased nonimpaired loans		35,440	30,887
Total loans, excluding covered loans		26,864,047	26,022,374
Commercial Real Estate
Ending balance of allowance attributable to loans:
Individually evaluated for impairment	[1]	3,690	3,725
Collectively evaluated for impairment	[1]	112,241	118,343
Total allowance for loan losses	[1]	115,931	122,068	139,271	138,233
Ending balance of loans:
Individually evaluated for impairment	[1]	52,021	80,123
Collectively evaluated for impairment	[1]	12,969,839	12,685,320
Purchased nonimpaired loans	[1]	33,045	42,090
Total loans, excluding covered loans	[1]	13,054,905	12,807,533
Residential
Ending balance of allowance attributable to loans:
Individually evaluated for impairment	[2]	35,841	38,126
Collectively evaluated for impairment	[2]	89,332	93,978
Total allowance for loan losses	[2]	125,173	132,104	144,947	154,627
Ending balance of loans:
Individually evaluated for impairment	[2]	176,695	183,473
Collectively evaluated for impairment	[2]	16,393,611	16,809,525
Purchased nonimpaired loans	[2]	900	906
Total loans, excluding covered loans	[2]	16,571,206	16,993,904
Consumer
Ending balance of allowance attributable to loans:
Individually evaluated for impairment	[3]	1,986	1,880
Collectively evaluated for impairment	[3]	110,565	103,068
Purchased nonimpaired	[3]	0	0
Total allowance for loan losses	[3]	112,551	104,948	$ 92,781	$ 89,891
Ending balance of loans:
Individually evaluated for impairment	[3]	2,880	2,789
Collectively evaluated for impairment	[3]	5,183,210	5,051,488
Purchased nonimpaired loans	[3]	4,623	5,035
Total loans, excluding covered loans	[3]	$ 5,190,713	$ 5,059,312

[1] Includes commercial real estate – mortgage and real estate – construction loans.

[2] Includes residential real estate – mortgage, equity lines of credit and equity loans.

[3] Includes credit card, consumer direct and consumer indirect loans.