Loans and Allowance for Credit Losses Allowance for Loan Losses by Portfolio Segment (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning Balance	$ 168,679	$ 169,054
Loans charged off	(9,407)	(11,155)
Recoveries of loans previously charged off	5,929	4,278
Net loans charged off	(3,478)	(6,877)
Provision for loan losses	4,875	1,664
Ending Balance	170,076	163,841
Provision for loan losses gross	75	134
Provision for credit losses	4,800	1,530
Real-estate - commercial mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning Balance	46,842	47,866
Loans charged off	(1,224)	(582)
Recoveries of loans previously charged off	450	825
Net loans charged off	(774)	243
Provision for loan losses	1,305	202
Ending Balance	47,373	48,311
Commercial - industrial, financial and agricultural
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning Balance	54,353	57,098
Loans charged off	(5,527)	(6,188)
Recoveries of loans previously charged off	4,191	2,319
Net loans charged off	(1,336)	(3,869)
Provision for loan losses	2,292	1,104
Ending Balance	55,309	54,333
Real-estate - home equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning Balance	26,801	22,405
Loans charged off	(698)	(1,541)
Recoveries of loans previously charged off	137	338
Net loans charged off	(561)	(1,203)
Provision for loan losses	(2,419)	1,322
Ending Balance	23,821	22,524
Real-estate - residential mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning Balance	22,929	21,375
Loans charged off	(216)	(1,068)
Recoveries of loans previously charged off	230	136
Net loans charged off	14	(932)
Provision for loan losses	(925)	(515)
Ending Balance	22,018	19,928
Real-estate - construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning Balance	6,455	6,529
Loans charged off	(247)	(326)
Recoveries of loans previously charged off	548	383
Net loans charged off	301	57
Provision for loan losses	745	(304)
Ending Balance	7,501	6,282
Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning Balance	3,574	2,585
Loans charged off	(856)	(1,007)
Recoveries of loans previously charged off	236	196
Net loans charged off	(620)	(811)
Provision for loan losses	77	550
Ending Balance	3,031	2,324
Leasing, other and overdrafts
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning Balance	3,192	2,468
Loans charged off	(639)	(443)
Recoveries of loans previously charged off	137	81
Net loans charged off	(502)	(362)
Provision for loan losses	578	868
Ending Balance	3,268	2,974
Unallocated
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning Balance	4,533	8,728
Loans charged off	0	0
Recoveries of loans previously charged off	0	0
Net loans charged off	0	0
Provision for loan losses	3,222	(1,563)
Ending Balance	$ 7,755	$ 7,165