Benefit Plans - Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Components of net periodic benefit cost:
Service cost	$ 1,347	$ 910	$ 548
Interest cost	1,642	1,794	1,107
Expected return on plan assets	(2,323)	(1,972)	(1,258)
Amortization of net loss	176	95	0
Amortization of prior service cost	1	3	0
Net periodic benefit cost	$ 843	$ 830	$ 397