Employee Benefit Plans - Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Retirement Benefits [Abstract]
Service cost	$ 338	$ 79	$ 1,014	$ 239
Interest cost	117	134	351	403
Net periodic benefit cost	$ 455	$ 213	$ 1,365	$ 642