Loans and Allowance for Loan Losses - Impaired loans by loan class (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015
Financing Receivable, Impaired [Line Items]
Individually evaluated impaired loans with no recorded allowance, recorded investment	$ 392,999		$ 80,358
Individually evaluated impaired loans with no recorded allowance, unpaid principle balance	407,177		91,318
Individually evaluated impaired loans with a recorded allowance, recorded investment	399,978		349,228
Individually evaluated impaired loans with a recorded allowance, unpaid principle balance	422,204		360,411
Individually evaluated impaired loans with a recorded allowance, allowance	100,660		71,217
Individually evaluated impaired loans, average recorded investment	593,071	$ 354,417
Individually evaluated impaired loans, interest income recognized	2,035	2,346
Commercial, Financial and Agricultural
Financing Receivable, Impaired [Line Items]
Individually evaluated impaired loans with no recorded allowance, recorded investment	365,382		45,583
Individually evaluated impaired loans with no recorded allowance, unpaid principle balance	376,828		53,325
Individually evaluated impaired loans with a recorded allowance, recorded investment	195,999		117,618
Individually evaluated impaired loans with a recorded allowance, unpaid principle balance	213,278		122,148
Individually evaluated impaired loans with a recorded allowance, allowance	59,143		27,486
Individually evaluated impaired loans, average recorded investment	343,028	64,881
Individually evaluated impaired loans, interest income recognized	320	339
Commercial Real Estate | Real estate – construction
Financing Receivable, Impaired [Line Items]
Individually evaluated impaired loans with no recorded allowance, recorded investment	3,374		3,403
Individually evaluated impaired loans with no recorded allowance, unpaid principle balance	3,986		3,986
Individually evaluated impaired loans with a recorded allowance, recorded investment	611		628
Individually evaluated impaired loans with a recorded allowance, unpaid principle balance	681		689
Individually evaluated impaired loans with a recorded allowance, allowance	497		515
Individually evaluated impaired loans, average recorded investment	3,999	6,115
Individually evaluated impaired loans, interest income recognized	2	39
Commercial Real Estate | Mortgage
Financing Receivable, Impaired [Line Items]
Individually evaluated impaired loans with no recorded allowance, recorded investment	24,243		24,851
Individually evaluated impaired loans with no recorded allowance, unpaid principle balance	26,363		27,486
Individually evaluated impaired loans with a recorded allowance, recorded investment	23,793		51,241
Individually evaluated impaired loans with a recorded allowance, unpaid principle balance	25,488		54,863
Individually evaluated impaired loans with a recorded allowance, allowance	3,193		3,210
Individually evaluated impaired loans, average recorded investment	60,504	88,178
Individually evaluated impaired loans, interest income recognized	413	580
Residential | Mortgage
Financing Receivable, Impaired [Line Items]
Individually evaluated impaired loans with no recorded allowance, recorded investment	0		6,521
Individually evaluated impaired loans with no recorded allowance, unpaid principle balance	0		6,521
Individually evaluated impaired loans with a recorded allowance, recorded investment	103,362		102,375
Individually evaluated impaired loans with a recorded allowance, unpaid principle balance	103,362		102,375
Individually evaluated impaired loans with a recorded allowance, allowance	6,964		7,370
Individually evaluated impaired loans, average recorded investment	108,918	113,926
Individually evaluated impaired loans, interest income recognized	636	695
Residential | Equity lines of credit
Financing Receivable, Impaired [Line Items]
Individually evaluated impaired loans with no recorded allowance, recorded investment	0		0
Individually evaluated impaired loans with no recorded allowance, unpaid principle balance	0		0
Individually evaluated impaired loans with a recorded allowance, recorded investment	27,679		28,164
Individually evaluated impaired loans with a recorded allowance, unpaid principle balance	30,145		30,302
Individually evaluated impaired loans with a recorded allowance, allowance	22,286		23,183
Individually evaluated impaired loans, average recorded investment	27,912	26,658
Individually evaluated impaired loans, interest income recognized	281	283
Residential | Equity loans
Financing Receivable, Impaired [Line Items]
Individually evaluated impaired loans with no recorded allowance, recorded investment	0		0
Individually evaluated impaired loans with no recorded allowance, unpaid principle balance	0		0
Individually evaluated impaired loans with a recorded allowance, recorded investment	45,654		46,413
Individually evaluated impaired loans with a recorded allowance, unpaid principle balance	46,365		47,245
Individually evaluated impaired loans with a recorded allowance, allowance	6,591		7,573
Individually evaluated impaired loans, average recorded investment	45,947	52,435
Individually evaluated impaired loans, interest income recognized	373	404
Consumer | Credit card
Financing Receivable, Impaired [Line Items]
Individually evaluated impaired loans with no recorded allowance, recorded investment	0		0
Individually evaluated impaired loans with no recorded allowance, unpaid principle balance	0		0
Individually evaluated impaired loans with a recorded allowance, recorded investment	0		0
Individually evaluated impaired loans with a recorded allowance, unpaid principle balance	0		0
Individually evaluated impaired loans with a recorded allowance, allowance	0		0
Individually evaluated impaired loans, average recorded investment	0	0
Individually evaluated impaired loans, interest income recognized	0	0
Consumer | Consumer direct
Financing Receivable, Impaired [Line Items]
Individually evaluated impaired loans with no recorded allowance, recorded investment	0		0
Individually evaluated impaired loans with no recorded allowance, unpaid principle balance	0		0
Individually evaluated impaired loans with a recorded allowance, recorded investment	889		935
Individually evaluated impaired loans with a recorded allowance, unpaid principle balance	889		935
Individually evaluated impaired loans with a recorded allowance, allowance	28		26
Individually evaluated impaired loans, average recorded investment	904	680
Individually evaluated impaired loans, interest income recognized	8	6
Consumer | Consumer indirect
Financing Receivable, Impaired [Line Items]
Individually evaluated impaired loans with no recorded allowance, recorded investment	0		0
Individually evaluated impaired loans with no recorded allowance, unpaid principle balance	0		0
Individually evaluated impaired loans with a recorded allowance, recorded investment	1,991		1,854
Individually evaluated impaired loans with a recorded allowance, unpaid principle balance	1,996		1,854
Individually evaluated impaired loans with a recorded allowance, allowance	1,958		$ 1,854
Individually evaluated impaired loans, average recorded investment	1,859	1,544
Individually evaluated impaired loans, interest income recognized	$ 2	$ 0