Loans and Allowance for Credit Losses Allowance for Loan Losses by Portfolio Segment (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning Balance	$ 170,076	$ 163,841	$ 168,679	$ 169,054
Loans charged off	(8,715)	(10,746)	(18,122)	(21,901)
Recoveries of loans previously charged off	4,366	7,278	10,295	11,556
Net loans charged off	(4,349)	(3,468)	(7,827)	(10,345)
Provision for loan losses	6,615	2,173	11,490	3,837
Ending Balance	172,342	162,546	172,342	162,546
Provision for loan losses gross	85	338	10	204
Provision for credit losses	6,700	2,511	11,500	4,041
Real-estate - commercial mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning Balance	47,373	48,311	46,842	47,866
Loans charged off	(242)	(1,474)	(1,466)	(2,056)
Recoveries of loans previously charged off	934	1,367	1,384	2,192
Net loans charged off	692	(107)	(82)	136
Provision for loan losses	9,307	(4,464)	10,612	(4,262)
Ending Balance	57,372	43,740	57,372	43,740
Commercial - industrial, financial and agricultural
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning Balance	55,309	54,333	54,353	57,098
Loans charged off	(5,353)	(4,625)	(10,880)	(10,813)
Recoveries of loans previously charged off	1,974	2,931	6,165	5,250
Net loans charged off	(3,379)	(1,694)	(4,715)	(5,563)
Provision for loan losses	15,712	(884)	18,004	220
Ending Balance	67,642	51,755	67,642	51,755
Real-estate - home equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning Balance	23,821	22,524	26,801	22,405
Loans charged off	(592)	(1,045)	(1,290)	(2,586)
Recoveries of loans previously charged off	215	350	352	688
Net loans charged off	(377)	(695)	(938)	(1,898)
Provision for loan losses	(5,988)	4,341	(8,407)	5,663
Ending Balance	17,456	26,170	17,456	26,170
Real estate - residential mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning Balance	22,018	19,928	22,929	21,375
Loans charged off	(124)	(340)	(340)	(1,408)
Recoveries of loans previously charged off	151	420	381	556
Net loans charged off	27	80	41	(852)
Provision for loan losses	(5,606)	1,218	(6,531)	703
Ending Balance	16,439	21,226	16,439	21,226
Real-estate - construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning Balance	7,501	6,282	6,455	6,529
Loans charged off	(774)	(742)	(1,021)	(1,068)
Recoveries of loans previously charged off	373	1,563	921	1,946
Net loans charged off	(401)	821	(100)	878
Provision for loan losses	2,434	(1,331)	3,179	(1,635)
Ending Balance	9,534	5,772	9,534	5,772
Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning Balance	3,031	2,324	3,574	2,585
Loans charged off	(430)	(569)	(1,286)	(1,576)
Recoveries of loans previously charged off	470	539	706	735
Net loans charged off	40	(30)	(580)	(841)
Provision for loan losses	(1,277)	690	(1,200)	1,240
Ending Balance	1,794	2,984	1,794	2,984
Leasing, other and overdrafts
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning Balance	3,268	2,974	3,192	2,468
Loans charged off	(1,200)	(1,951)	(1,839)	(2,394)
Recoveries of loans previously charged off	249	108	386	189
Net loans charged off	(951)	(1,843)	(1,453)	(2,205)
Provision for loan losses	(212)	1,387	366	2,255
Ending Balance	2,105	2,518	2,105	2,518
Unallocated
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning Balance	7,755	7,165	4,533	8,728
Loans charged off	0	0	0	0
Recoveries of loans previously charged off	0	0	0	0
Net loans charged off	0	0	0	0
Provision for loan losses	(7,755)	1,216	(4,533)	(347)
Ending Balance	$ 0	$ 8,381	$ 0	$ 8,381