Loans - Allowance for Loan Losses and Recorded Investment in Loans by Portfolio Segment (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2017
Ending allowance balance attributable to loans:
Individually evaluated for impairment	$ 642	$ 168
Collectively evaluated for impairment	14,838	14,982
Modified in a troubled debt restructuring	4,866	4,554
Total ending allowance balance	20,346	19,704	$ 20,756	$ 19,693
Loans:
Individually evaluated for impairment	3,720	3,292
Collectively evaluated for impairment	2,513,386	2,460,863
Total ending loans balance	2,530,761	2,479,348
Modified in a troubled debt restructuring	13,099	14,626
Acquired with deteriorated credit quality
Ending allowance balance attributable to loans:
Total ending allowance balance	0	0
Loans:
Total ending loans balance	556	567
Commercial, Industrial, and Agricultural
Ending allowance balance attributable to loans:
Individually evaluated for impairment	330	54
Collectively evaluated for impairment	7,350	7,183
Modified in a troubled debt restructuring	107	104
Total ending allowance balance	7,787	7,341	6,282	6,160
Loans:
Individually evaluated for impairment	1,754	1,334
Collectively evaluated for impairment	945,710	910,386
Total ending loans balance	950,865	916,297
Modified in a troubled debt restructuring	3,401	4,577
Commercial, Industrial, and Agricultural | Acquired with deteriorated credit quality
Ending allowance balance attributable to loans:
Total ending allowance balance	0	0
Loans:
Total ending loans balance	0	0
Commercial mortgages
Ending allowance balance attributable to loans:
Individually evaluated for impairment	312	4
Collectively evaluated for impairment	3,775	3,036
Modified in a troubled debt restructuring	4,759	4,450
Total ending allowance balance	8,846	7,490	10,020	9,007
Loans:
Individually evaluated for impairment	1,468	1,446
Collectively evaluated for impairment	698,004	685,714
Total ending loans balance	709,726	697,776
Modified in a troubled debt restructuring	9,698	10,049
Commercial mortgages | Acquired with deteriorated credit quality
Ending allowance balance attributable to loans:
Total ending allowance balance	0	0
Loans:
Total ending loans balance	556	567
Residential Real Estate
Ending allowance balance attributable to loans:
Individually evaluated for impairment	0	100
Collectively evaluated for impairment	1,383	2,056
Modified in a troubled debt restructuring	0	0
Total ending allowance balance	1,383	2,156	2,052	2,033
Loans:
Individually evaluated for impairment	498	502
Collectively evaluated for impairment	775,101	770,807
Total ending loans balance	775,599	771,309
Modified in a troubled debt restructuring	0	0
Residential Real Estate | Acquired with deteriorated credit quality
Ending allowance balance attributable to loans:
Total ending allowance balance	0	0
Loans:
Total ending loans balance	0	0
Consumer
Ending allowance balance attributable to loans:
Individually evaluated for impairment	0	0
Collectively evaluated for impairment	2,040	2,377
Modified in a troubled debt restructuring	0	0
Total ending allowance balance	2,040	2,377	2,065	2,179
Loans:
Individually evaluated for impairment	0	0
Collectively evaluated for impairment	86,780	86,035
Total ending loans balance	86,780	86,035
Modified in a troubled debt restructuring	0	0
Consumer | Acquired with deteriorated credit quality
Ending allowance balance attributable to loans:
Total ending allowance balance	0	0
Loans:
Total ending loans balance	0	0
Credit Cards
Ending allowance balance attributable to loans:
Individually evaluated for impairment	0	0
Collectively evaluated for impairment	105	103
Modified in a troubled debt restructuring	0	0
Total ending allowance balance	105	103	123	120
Loans:
Individually evaluated for impairment	0	0
Collectively evaluated for impairment	7,341	7,623
Total ending loans balance	7,341	7,623
Modified in a troubled debt restructuring	0	0
Credit Cards | Acquired with deteriorated credit quality
Ending allowance balance attributable to loans:
Total ending allowance balance	0	0
Loans:
Total ending loans balance	0	0
Overdrafts
Ending allowance balance attributable to loans:
Individually evaluated for impairment	0	10
Collectively evaluated for impairment	185	227
Modified in a troubled debt restructuring	0	0
Total ending allowance balance	185	237	$ 214	$ 194
Loans:
Individually evaluated for impairment	0	10
Collectively evaluated for impairment	450	298
Total ending loans balance	450	308
Modified in a troubled debt restructuring	0	0
Overdrafts | Acquired with deteriorated credit quality
Ending allowance balance attributable to loans:
Total ending allowance balance	0	0
Loans:
Total ending loans balance	$ 0	$ 0