Employee Benefit Plans - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Requisite service period	3 years
Accumulated benefit obligation	$ 11,800	$ 10,600
Future amortization of prior service cost (credit)	$ 247
Maximum annual contributions per employee, percent	20.00%
Employer matching contribution, percent	4.00%
Employer discretionary contribution amount	$ 206	196
Supplemental Employee Retirement Plans, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Benefit plan retirement age	65 years
Plan liabilities	$ 1,200	1,100
Benefit expense	167	114
Board of Directors
Defined Benefit Plan Disclosure [Line Items]
Employer discretionary contribution amount	$ 109	$ 105