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, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning Balance	$ 162,109	$ 163,217	$ 160,537	$ 169,910
Loans and leases charged off	(3,711)	(42,160)	(10,080)	(48,557)
Recoveries of loans and leases previously charged off	5,255	2,271	7,486	4,633
Net loans and leases recovered (charged off)	1,544	(39,889)	(2,594)	(43,924)
Provision for loan losses	6,580	32,722	12,290	30,064
Ending Balance	170,233	156,050	170,233	156,050
Provision for loan losses gross	(1,600)	395	(2,200)	7,000
Provision for credit losses	5,025	33,117	10,125	37,087
Real-estate - commercial mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning Balance	51,946	58,717	52,889	58,793
Loans and leases charged off	(230)	(366)	(1,375)	(633)
Recoveries of loans and leases previously charged off	169	321	305	600
Net loans and leases recovered (charged off)	(61)	(45)	(1,070)	(33)
Provision for loan losses	2,974	(2,089)	3,040	(2,177)
Ending Balance	54,859	56,583	54,859	56,583
Commercial - industrial, financial and agricultural
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning Balance	60,501	61,830	58,868	66,280
Loans and leases charged off	(1,895)	(38,632)	(4,682)	(42,637)
Recoveries of loans and leases previously charged off	2,680	541	3,923	1,616
Net loans and leases recovered (charged off)	785	(38,091)	(759)	(41,021)
Provision for loan losses	5,055	35,306	8,232	33,786
Ending Balance	66,341	59,045	66,341	59,045
Real-estate - home equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning Balance	19,215	17,528	18,911	18,127
Loans and leases charged off	(206)	(816)	(425)	(1,224)
Recoveries of loans and leases previously charged off	223	271	420	477
Net loans and leases recovered (charged off)	17	(545)	(5)	(747)
Provision for loan losses	(251)	(736)	75	(1,133)
Ending Balance	18,981	16,247	18,981	16,247
Real estate - residential mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning Balance	19,146	15,261	18,921	16,088
Loans and leases charged off	(134)	(483)	(789)	(645)
Recoveries of loans and leases previously charged off	211	96	343	203
Net loans and leases recovered (charged off)	77	(387)	(446)	(442)
Provision for loan losses	(331)	(370)	417	(1,142)
Ending Balance	18,892	14,504	18,892	14,504
Real estate - construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning Balance	4,941	5,924	5,061	6,620
Loans and leases charged off	(3)	(606)	(98)	(764)
Recoveries of loans and leases previously charged off	1,245	444	1,329	750
Net loans and leases recovered (charged off)	1,242	(162)	1,231	(14)
Provision for loan losses	(1,255)	226	(1,364)	(618)
Ending Balance	4,928	5,988	4,928	5,988
Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning Balance	3,319	1,903	3,217	2,045
Loans and leases charged off	(795)	(712)	(1,478)	(1,604)
Recoveries of loans and leases previously charged off	579	446	789	625
Net loans and leases recovered (charged off)	(216)	(266)	(689)	(979)
Provision for loan losses	260	62	835	633
Ending Balance	3,363	1,699	3,363	1,699
Equipment lease financing, other and overdrafts
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning Balance	3,041	2,054	2,670	1,957
Loans and leases charged off	(448)	(545)	(1,233)	(1,050)
Recoveries of loans and leases previously charged off	148	152	377	362
Net loans and leases recovered (charged off)	(300)	(393)	(856)	(688)
Provision for loan losses	128	323	1,055	715
Ending Balance	$ 2,869	$ 1,984	$ 2,869	$ 1,984