Employee Benefits - Components of Net Periodic Pension Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Service cost	$ 3,145	$ 2,820	$ 2,780
Interest cost	840	765	850
Expected return on plan assets	(475)	(360)	(375)
Recognition of actuarial loss	340	350	200
Total defined benefit pension expense	$ 3,850	$ 3,575	$ 3,455