Pension and Other Postretirement Benefit Plans Components of Net Periodic Pension Costs (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Compensation And Retirement Disclosure [Abstract]
Service cost		$ 755	$ 1,453
Interest cost	$ 679	1,027	1,244
Expected return on plan assets	(634)	(914)	(1,077)
Administrative charges		17	37
Curtailment	(1,049)	(2,621)	(1,219)
Prior service cost		(848)	(106)
Net actuarial loss		3,171	1,706
Net periodic pension cost	$ (1,004)	$ 587	$ 2,038