Employee Benefit Plans - Changes in the Benefit Obligation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Projected benefit obligation, beginning	$ 13,436	$ 11,337
Service cost	319	1,310	$ 1,323
Interest cost	537	453	383
Actuarial experience and changes in actuarial assumptions	117	336
Projected benefit obligation, ending	$ 14,409	$ 13,436	$ 11,337