Loans and Allowance for Loan Losses - Allowances for loan losses activity (Details) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2018	Mar. 31, 2017
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan losses, covered, beginning of period		$ 0	$ 0
Allowance for loan losses, total loans, beginning of period		842,760	838,293
Provision (credit) for loan losses		57,029	80,139
Provision (credit) for loan losses, covered		0	(31)
Provision (credit) for loan losses, total loans		57,029	80,139
Loans charged off, covered		0	0
Loans charged off, total loans		(83,301)	(102,188)
Loan recoveries, covered		0	31
Loan recoveries, total loans		15,583	17,862
Net (charge offs) recoveries, covered		0	31
Net (charge offs) recoveries, total loans		(67,718)	(84,326)
Allowance for loan losses, covered, end of period		0	0
Allowance for loan losses, total loans, end of period		832,071	834,106
Commercial, Financial and Agricultural
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan losses, beginning of period		420,635	458,580
Provision (credit) for loan losses		(14,097)	40,045
Loans charged off		(10,132)	(42,908)
Loan recoveries		1,737	3,497
Net (charge offs) recoveries		(8,395)	(39,411)
Allowance for loan losses, end of period		398,143	459,214
Commercial Real Estate
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan losses, beginning of period	[1]	118,133	116,937
Provision (credit) for loan losses	[1]	3,667	(3,128)
Loans charged off	[1]	(203)	(114)
Loan recoveries	[1]	178	912
Net (charge offs) recoveries	[1]	(25)	798
Allowance for loan losses, end of period	[1]	121,775	114,607
Residential Real Estate
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan losses, beginning of period	[2]	109,856	119,484
Provision (credit) for loan losses	[2]	(2,531)	(330)
Loans charged off	[2]	(4,582)	(6,338)
Loan recoveries	[2]	3,111	3,129
Net (charge offs) recoveries	[2]	(1,471)	(3,209)
Allowance for loan losses, end of period	[2]	105,854	115,945
Consumer
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan losses, beginning of period	[3]	194,136	143,292
Provision (credit) for loan losses	[3]	69,990	43,583
Loans charged off	[3]	(68,384)	(52,828)
Loan recoveries	[3]	10,557	10,293
Net (charge offs) recoveries	[3]	(57,827)	(42,535)
Allowance for loan losses, end of period	[3]	$ 206,299	$ 144,340

[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.