Comprehensive Income - Components of Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income	$ (1,871)	$ (1,453)
Defined Benefit Pension Plan
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net unrealized actuarial gain (loss)	(2,628)	(2,694)
Tax effect	552	914
Accumulated other comprehensive income	(2,076)	(1,780)
Securities Available for Sale | Accumulated Net Investment Gain (Loss)
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net unrealized actuarial gain (loss)	0	283
Tax effect	0	(140)
Accumulated other comprehensive income	0	143
Securities Held to Maturity | Accumulated Net Investment Gain (Loss)
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net unrealized actuarial gain (loss)	231	250
Tax effect	(26)	(66)
Accumulated other comprehensive income	$ 205	$ 184