Other Comprehensive Income - Components of Other Comprehensive Income and Related Tax Effects (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total other comprehensive income (loss)	$ 8,135	$ 10,935	$ (3,653)
Available for sale securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Before reclassifications	12,494	13,732	(5,073)
Reclassifications	(2,190)	(148)	0
Net unrealized gain (loss)	10,304	13,584	(5,073)
Tax effect	(2,164)	(2,852)	1,066
Total other comprehensive income (loss)	8,140	10,732	(4,007)
Unrealized gain (loss) on postretirement benefits plan
Accumulated Other Comprehensive Income (Loss) [Line Items]
Before reclassifications	277	518	404
Reclassifications	0	23	84
Net unrealized gain (loss)	277	541	488
Tax effect	(58)	(113)	(102)
Total other comprehensive income (loss)	219	428	386
Unrealized loss on interest rate swap
Accumulated Other Comprehensive Income (Loss) [Line Items]
Before reclassifications	(508)	(347)	(204)
Reclassifications	224	63	164
Net unrealized gain (loss)	(284)	(284)	(40)
Tax effect	60	59	8
Total other comprehensive income (loss)	$ (224)	$ (225)	$ (32)