Employee Benefit Plans - Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Retirement Benefits [Abstract]
Service cost	$ 1,353	$ 319	$ 1,310
Interest cost	468	537	453
Net periodic benefit cost	$ 1,821	$ 856	$ 1,763