Loans - Allowance for Loan Losses and Recorded Investment in Loans by Portfolio Segment (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Jun. 30, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Dec. 31, 2017
Ending allowance balance attributable to loans:
Individually evaluated for impairment	$ 2,849		$ 168
Collectively evaluated for impairment	16,798		14,982
Modified in a troubled debt restructuring	560		4,554
Total ending allowance balance	20,207	$ 21,437	19,704	$ 22,510	$ 22,122	$ 19,693
Loans:
Individually evaluated for impairment	6,497		3,292
Collectively evaluated for impairment	2,739,691		2,460,863
Modified in a troubled debt restructuring, collective pool	7,847
Modified in a troubled debt restructuring	10,199		14,626
Total ending loans balance	2,754,569		2,479,348
Acquired with deteriorated credit quality
Ending allowance balance attributable to loans:
Total ending allowance balance	0		0
Loans:
Total ending loans balance	534		567
Commercial, Industrial, and Agricultural
Ending allowance balance attributable to loans:
Individually evaluated for impairment	766		54
Collectively evaluated for impairment	8,148		7,183
Modified in a troubled debt restructuring	36		104
Total ending allowance balance	8,950	8,108	7,341	6,580	7,143	6,160
Loans:
Individually evaluated for impairment	2,898		1,334
Collectively evaluated for impairment	1,027,732		910,386
Modified in a troubled debt restructuring, collective pool	3,001
Modified in a troubled debt restructuring	3,197		4,577
Total ending loans balance	1,033,631		916,297
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	2,054		4
Collectively evaluated for impairment	4,405		3,036
Modified in a troubled debt restructuring	524		4,450
Total ending allowance balance	6,983	9,538	7,490	11,297	10,615	9,007
Loans:
Individually evaluated for impairment	3,110		1,446
Collectively evaluated for impairment	780,484		685,714
Modified in a troubled debt restructuring, collective pool	4,846
Modified in a troubled debt restructuring	7,002		10,049
Total ending loans balance	788,974		697,776
Commercial mortgages | Acquired with deteriorated credit quality
Ending allowance balance attributable to loans:
Total ending allowance balance	0		0
Loans:
Total ending loans balance	534		567
Residential Real Estate
Ending allowance balance attributable to loans:
Individually evaluated for impairment	29		100
Collectively evaluated for impairment	1,457		2,056
Modified in a troubled debt restructuring	0		0
Total ending allowance balance	1,486	1,403	2,156	1,978	1,900	2,033
Loans:
Individually evaluated for impairment	489		502
Collectively evaluated for impairment	801,842		770,807
Modified in a troubled debt restructuring, collective pool	0
Modified in a troubled debt restructuring	0		0
Total ending loans balance	802,331		771,309
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	2,345		2,377
Modified in a troubled debt restructuring	0		0
Total ending allowance balance	2,345	2,141	2,377	2,323	2,156	2,179
Loans:
Individually evaluated for impairment	0		0
Collectively evaluated for impairment	121,598		86,035
Modified in a troubled debt restructuring, collective pool	0
Modified in a troubled debt restructuring	0		0
Total ending loans balance	121,598		86,035
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	87	103	107	101	120
Loans:
Individually evaluated for impairment	0		0
Collectively evaluated for impairment	7,393		7,623
Modified in a troubled debt restructuring, collective pool	0
Modified in a troubled debt restructuring	0		0
Total ending loans balance	7,393		7,623
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	338		227
Modified in a troubled debt restructuring	0		0
Total ending allowance balance	338	$ 160	237	$ 225	$ 207	$ 194
Loans:
Individually evaluated for impairment	0		10
Collectively evaluated for impairment	642		298
Modified in a troubled debt restructuring, collective pool	0
Modified in a troubled debt restructuring			0
Total ending loans balance	642		308
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