Employee Benefits - Components of Net Periodic Pension Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Service cost	$ 4,421	$ 3,659	$ 3,145
Interest cost	718	851	840
Expected return on plan assets	(493)	(517)	(475)
Recognition of actuarial loss	474	237	340
Total defined benefit pension expense	$ 5,120	$ 4,230	$ 3,850