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, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning Balance	$ 163,217	$ 170,076	$ 169,910	$ 168,679
Loans charged off	(42,160)	(8,715)	(48,557)	(18,122)
Recoveries of loans previously charged off	2,271	4,366	4,633	10,295
Net loans charged off	(39,889)	(4,349)	(43,924)	(7,827)
Provision for loan losses	32,722	6,615	30,064	11,490
Ending Balance	156,050	172,342	156,050	172,342
Provision for loan losses gross	400	100	7,000	0
Provision for credit losses	33,117	6,700	37,087	11,500
Real-estate - commercial mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning Balance	58,717	47,373	58,793	46,842
Loans charged off	(366)	(242)	(633)	(1,466)
Recoveries of loans previously charged off	321	934	600	1,384
Net loans charged off	(45)	692	(33)	(82)
Provision for loan losses	(2,089)	9,307	(2,177)	10,612
Ending Balance	56,583	57,372	56,583	57,372
Commercial - industrial, financial and agricultural
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning Balance	61,830	55,309	66,280	54,353
Loans charged off	(38,632)	(5,353)	(42,637)	(10,880)
Recoveries of loans previously charged off	541	1,974	1,616	6,165
Net loans charged off	(38,091)	(3,379)	(41,021)	(4,715)
Provision for loan losses	35,306	15,712	33,786	18,004
Ending Balance	59,045	67,642	59,045	67,642
Real-estate - home equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning Balance	17,528	23,821	18,127	26,801
Loans charged off	(816)	(592)	(1,224)	(1,290)
Recoveries of loans previously charged off	271	215	477	352
Net loans charged off	(545)	(377)	(747)	(938)
Provision for loan losses	(736)	(5,988)	(1,133)	(8,407)
Ending Balance	16,247	17,456	16,247	17,456
Real estate - residential mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning Balance	15,261	22,018	16,088	22,929
Loans charged off	(483)	(124)	(645)	(340)
Recoveries of loans previously charged off	96	151	203	381
Net loans charged off	(387)	27	(442)	41
Provision for loan losses	(370)	(5,606)	(1,142)	(6,531)
Ending Balance	14,504	16,439	14,504	16,439
Real-estate - construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning Balance	5,924	7,501	6,620	6,455
Loans charged off	(606)	(774)	(764)	(1,021)
Recoveries of loans previously charged off	444	373	750	921
Net loans charged off	(162)	(401)	(14)	(100)
Provision for loan losses	226	2,434	(618)	3,179
Ending Balance	5,988	9,534	5,988	9,534
Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning Balance	1,903	3,031	2,045	3,574
Loans charged off	(712)	(430)	(1,604)	(1,286)
Recoveries of loans previously charged off	446	470	625	706
Net loans charged off	(266)	40	(979)	(580)
Provision for loan losses	62	(1,277)	633	(1,200)
Ending Balance	1,699	1,794	1,699	1,794
Leasing, other and overdrafts
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning Balance	2,054	3,268	1,957	3,192
Loans charged off	(545)	(1,200)	(1,050)	(1,839)
Recoveries of loans previously charged off	152	249	362	386
Net loans charged off	(393)	(951)	(688)	(1,453)
Provision for loan losses	323	(212)	715	366
Ending Balance	1,984	2,105	1,984	2,105
Unallocated
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning Balance	0	7,755	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	(7,755)	0	(4,533)
Ending Balance	$ 0	$ 0	$ 0	$ 0