Employee Benefit Plans - Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Net periodic benefit cost
Service cost	$ 6,047	$ 5,195	$ 4,450
Interest cost	193	345	278
Expected return on plan assets	(126)	(241)	(195)
Amortization of prior service cost	216	214	179
Amortization of actuarial losses	667	247	265
Net periodic benefit cost	$ 6,997	$ 5,760	$ 4,977
Location of costs excluding the service component	us-gaap:OtherNonoperatingIncomeExpense	us-gaap:OtherNonoperatingIncomeExpense	us-gaap:OtherNonoperatingIncomeExpense