Employee Benefit Plans - Net Periodic Benefit Plan (Income) Cost for the Postretirement Plan (Details) - Postretirement Plan - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Changes recognized in accumulated other comprehensive income (loss)
Accumulated other comprehensive income (loss) before tax, beginning of period	$ (193)	$ (239)	$ (285)
Amortization of prior service cost	46	46	46
Accumulated other comprehensive income (loss) before tax, end of period	(147)	(193)	(239)
Prior service credits expected to be recognized as components of net periodic benefit cost	46
Net periodic benefit plan (income) cost included in other non-interest expense
Interest cost	110	133	151
Recognized actuarial (gain) loss	(115)	(248)	(211)
Amortization of prior service cost	(46)	(46)	(46)
Net periodic benefit plan (income) cost	$ (51)	$ (161)	$ (106)
Discount rate used to determine the estimated net periodic benefit plan (income) cost	3.15%	3.40%	3.50%