Loans and Allowance for Loan Losses - Allowances for loan losses activity (Details) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2017	Mar. 31, 2016
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan losses, covered, beginning of period		$ 0	$ 1,440
Allowance for loan losses, total loans, beginning of period		838,293	762,673
Provision (credit) for loan losses		80,139	113,245
Provision (credit) for loan losses, covered		(31)	(44)
Provision (credit) for loan losses, total loans		80,139	113,245
Loans charged off, covered		0	(249)
Loans charged off, total loans		(102,188)	(66,898)
Loan recoveries, covered		31	0
Loan recoveries, total loans		17,862	13,420
Net (charge offs) recoveries, covered		31	(249)
Net (charge offs) recoveries, total loans		(84,326)	(53,478)
Allowance for loan losses, covered, end of period		0	1,147
Allowance for loan losses, total loans, end of period		834,106	822,440
Commercial, Financial and Agricultural
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan losses, beginning of period		458,580	402,113
Provision (credit) for loan losses		40,045	83,582
Loans charged off		(42,908)	(19,806)
Loan recoveries		3,497	1,749
Net (charge offs) recoveries		(39,411)	(18,057)
Allowance for loan losses, end of period		459,214	467,638
Commercial Real Estate
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan losses, beginning of period	[1]	116,937	122,068
Provision (credit) for loan losses	[1]	(3,128)	(6,417)
Loans charged off	[1]	(114)	(689)
Loan recoveries	[1]	912	969
Net (charge offs) recoveries	[1]	798	280
Allowance for loan losses, end of period	[1]	114,607	115,931
Residential Real Estate
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan losses, beginning of period	[2]	119,484	132,104
Provision (credit) for loan losses	[2]	(330)	(3,149)
Loans charged off	[2]	(6,338)	(6,201)
Loan recoveries	[2]	3,129	2,419
Net (charge offs) recoveries	[2]	(3,209)	(3,782)
Allowance for loan losses, end of period	[2]	115,945	125,173
Consumer
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan losses, beginning of period	[3]	143,292	104,948
Provision (credit) for loan losses	[3]	43,583	39,273
Loans charged off	[3]	(52,828)	(39,953)
Loan recoveries	[3]	10,293	8,283
Net (charge offs) recoveries	[3]	(42,535)	(31,670)
Allowance for loan losses, end of period	[3]	$ 144,340	$ 112,551

[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.