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, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning Balance	$ 156,050	$ 172,342	$ 169,910	$ 168,679
Loans charged off	(6,883)	(7,795)	(55,440)	(25,917)
Recoveries of loans previously charged off	3,842	2,471	8,475	12,766
Net loans charged off	(3,041)	(5,324)	(46,965)	(13,151)
Provision for loan losses	4,801	5,227	34,865	16,717
Ending Balance	157,810	172,245	157,810	172,245
Provision for loan losses gross	3,200	152	3,800	142
Provision for credit losses	1,620	5,075	38,707	16,575
Real-estate - commercial mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning Balance	56,583	57,372	58,793	46,842
Loans charged off	(650)	(483)	(1,283)	(1,949)
Recoveries of loans previously charged off	928	106	1,528	1,490
Net loans charged off	278	(377)	245	(459)
Provision for loan losses	(2,750)	(2,008)	(4,927)	8,604
Ending Balance	54,111	54,987	54,111	54,987
Commercial - industrial, financial and agricultural
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning Balance	59,045	67,642	66,280	54,353
Loans charged off	(3,541)	(2,714)	(46,178)	(13,594)
Recoveries of loans previously charged off	731	665	2,347	6,830
Net loans charged off	(2,810)	(2,049)	(43,831)	(6,764)
Provision for loan losses	(301)	5,392	33,485	23,396
Ending Balance	55,934	70,985	55,934	70,985
Real-estate - home equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning Balance	16,247	17,456	18,127	26,801
Loans charged off	(743)	(547)	(1,967)	(1,837)
Recoveries of loans previously charged off	217	252	694	604
Net loans charged off	(526)	(295)	(1,273)	(1,233)
Provision for loan losses	2,890	1,297	1,757	(7,110)
Ending Balance	18,611	18,458	18,611	18,458
Real estate - residential mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning Balance	14,504	16,439	16,088	22,929
Loans charged off	(483)	(195)	(1,128)	(535)
Recoveries of loans previously charged off	317	219	520	600
Net loans charged off	(166)	24	(608)	65
Provision for loan losses	3,774	220	2,632	(6,311)
Ending Balance	18,112	16,683	18,112	16,683
Real-estate - construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning Balance	5,988	9,534	6,620	6,455
Loans charged off	(212)	(2,744)	(976)	(3,765)
Recoveries of loans previously charged off	664	629	1,414	1,550
Net loans charged off	452	(2,115)	438	(2,215)
Provision for loan losses	(961)	(283)	(1,579)	2,896
Ending Balance	5,479	7,136	5,479	7,136
Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning Balance	1,699	1,794	2,045	3,574
Loans charged off	(672)	(373)	(2,276)	(1,659)
Recoveries of loans previously charged off	390	193	1,015	899
Net loans charged off	(282)	(180)	(1,261)	(760)
Provision for loan losses	1,429	383	2,062	(817)
Ending Balance	2,846	1,997	2,846	1,997
Leasing, other and overdrafts
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning Balance	1,984	2,105	1,957	3,192
Loans charged off	(582)	(739)	(1,632)	(2,578)
Recoveries of loans previously charged off	595	407	957	793
Net loans charged off	13	(332)	(675)	(1,785)
Provision for loan losses	720	226	1,435	592
Ending Balance	2,717	1,999	2,717	1,999
Unallocated
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning Balance	0	0	0	4,533
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	0	0	(4,533)
Ending Balance	$ 0	$ 0	$ 0	$ 0