Loans and Allowance for Credit Losses Allowance for Loan Losses by Portfolio Segment (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning Balance	$ 172,342	$ 162,546	$ 168,679	$ 169,054
Loans charged off	(7,795)	(7,672)	(25,917)	(29,573)
Recoveries of loans previously charged off	2,471	3,592	12,766	15,148
Net loans charged off	(5,324)	(4,080)	(13,151)	(14,425)
Provision for loan losses	5,227	4,060	16,717	7,897
Ending Balance	172,245	162,526	172,245	162,526
Provision for loan losses gross	(152)	81	(142)	285
Provision for credit losses	5,075	4,141	16,575	8,182
Real-estate - commercial mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning Balance	57,372	43,740	46,842	47,866
Loans charged off	(483)	(1,350)	(1,949)	(3,406)
Recoveries of loans previously charged off	106	296	1,490	2,488
Net loans charged off	(377)	(1,054)	(459)	(918)
Provision for loan losses	(2,008)	3,171	8,604	(1,091)
Ending Balance	54,987	45,857	54,987	45,857
Commercial - industrial, financial and agricultural
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning Balance	67,642	51,755	54,353	57,098
Loans charged off	(2,714)	(3,144)	(13,594)	(13,957)
Recoveries of loans previously charged off	665	1,539	6,830	6,789
Net loans charged off	(2,049)	(1,605)	(6,764)	(7,168)
Provision for loan losses	5,392	(1,871)	23,396	(1,651)
Ending Balance	70,985	48,279	70,985	48,279
Real-estate - home equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning Balance	17,456	26,170	26,801	22,405
Loans charged off	(547)	(709)	(1,837)	(3,295)
Recoveries of loans previously charged off	252	241	604	929
Net loans charged off	(295)	(468)	(1,233)	(2,366)
Provision for loan losses	1,297	1,419	(7,110)	7,082
Ending Balance	18,458	27,121	18,458	27,121
Real estate - residential mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning Balance	16,439	21,226	22,929	21,375
Loans charged off	(195)	(802)	(535)	(2,210)
Recoveries of loans previously charged off	219	228	600	784
Net loans charged off	24	(574)	65	(1,426)
Provision for loan losses	220	1,452	(6,311)	2,155
Ending Balance	16,683	22,104	16,683	22,104
Real-estate - construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning Balance	9,534	5,772	6,455	6,529
Loans charged off	(2,744)	(150)	(3,765)	(1,218)
Recoveries of loans previously charged off	629	898	1,550	2,844
Net loans charged off	(2,115)	748	(2,215)	1,626
Provision for loan losses	(283)	23	2,896	(1,612)
Ending Balance	7,136	6,543	7,136	6,543
Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning Balance	1,794	2,984	3,574	2,585
Loans charged off	(373)	(685)	(1,659)	(2,261)
Recoveries of loans previously charged off	193	222	899	957
Net loans charged off	(180)	(463)	(760)	(1,304)
Provision for loan losses	383	852	(817)	2,092
Ending Balance	1,997	3,373	1,997	3,373
Leasing, other and overdrafts
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning Balance	2,105	2,518	3,192	2,468
Loans charged off	(739)	(832)	(2,578)	(3,226)
Recoveries of loans previously charged off	407	168	793	357
Net loans charged off	(332)	(664)	(1,785)	(2,869)
Provision for loan losses	226	1,075	592	3,330
Ending Balance	1,999	2,929	1,999	2,929
Unallocated
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning Balance	0	8,381	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	0	(2,061)	(4,533)	(2,408)
Ending Balance	$ 0	$ 6,320	$ 0	$ 6,320