Loans - Impaired Loans (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Average recorded investment
Impaired loans with a valuation allowance	$ 64,609	$ 28,176	$ 66,383	$ 33,654
Impaired loans with no related valuation allowance	42,184	86,400	39,969	86,167
Total impaired loans	106,793	114,576	106,352	119,821
Interest income recognized while on impaired status
Impaired loans with a valuation allowance	491	333	1,176	666
Impaired loans with no related valuation allowance	162	624	304	1,287
Total impaired loans	653	957	1,480	1,953
Commercial
Average recorded investment
Impaired loans with a valuation allowance	24,493	3,867	25,103	7,209
Impaired loans with no related valuation allowance	11,010	32,502	10,153	31,952
Total impaired loans	35,503	36,369	35,256	39,161
Interest income recognized while on impaired status
Impaired loans with a valuation allowance	201	0	425	0
Impaired loans with no related valuation allowance	48	310	78	587
Total impaired loans	249	310	503	587
Commercial real estate
Average recorded investment
Impaired loans with a valuation allowance	19,026	3,360	19,530	5,476
Impaired loans with no related valuation allowance	25,183	45,679	24,329	45,708
Total impaired loans	44,209	49,039	43,859	51,184
Interest income recognized while on impaired status
Impaired loans with a valuation allowance	202	0	405	0
Impaired loans with no related valuation allowance	99	312	203	692
Total impaired loans	301	312	608	692
Real estate construction and land development
Average recorded investment
Impaired loans with a valuation allowance	141	0	151	0
Impaired loans with no related valuation allowance	106	860	93	889
Total impaired loans	247	860	244	889
Interest income recognized while on impaired status
Impaired loans with a valuation allowance	3	0	5	0
Impaired loans with no related valuation allowance	0	2	0	8
Total impaired loans	3	2	5	8
Residential mortgage
Average recorded investment
Impaired loans with a valuation allowance	16,243	20,949	16,821	20,969
Impaired loans with no related valuation allowance	4,581	5,094	4,194	5,121
Total impaired loans	20,824	26,043	21,015	26,090
Interest income recognized while on impaired status
Impaired loans with a valuation allowance	68	333	302	666
Impaired loans with no related valuation allowance	10	0	17	0
Total impaired loans	78	333	319	666
Consumer installment
Average recorded investment
Impaired loans with a valuation allowance	682	0	731	0
Impaired loans with no related valuation allowance	142	281	179	311
Total impaired loans	824	281	910	311
Interest income recognized while on impaired status
Impaired loans with a valuation allowance	1	0	2	0
Impaired loans with no related valuation allowance	0	0	0	0
Total impaired loans	1	0	2	0
Home equity
Average recorded investment
Impaired loans with a valuation allowance	4,024	0	4,047	0
Impaired loans with no related valuation allowance	1,162	1,984	1,021	2,186
Total impaired loans	5,186	1,984	5,068	2,186
Interest income recognized while on impaired status
Impaired loans with a valuation allowance	16	0	37	0
Impaired loans with no related valuation allowance	5	0	6	0
Total impaired loans	$ 21	$ 0	$ 43	$ 0