Employee Benefit Plans - Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Retirement Benefits [Abstract]
Service cost	$ 338	$ 80	$ 676	$ 160
Interest cost	117	135	234	269
Net periodic benefit cost	$ 455	$ 215	$ 910	$ 429