Pension and Other Postretirement Benefit Plans Components of Net Periodic Pension Costs (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Compensation And Retirement Disclosure [Abstract]
Service cost	$ 755	$ 1,453	$ 1,494
Interest cost	1,027	1,244	1,121
Expected return on plan assets	(914)	(1,077)	(950)
Administrative charges	17	37
Curtailment	(2,621)	(1,219)
Prior service cost	(848)	(106)	(77)
Net actuarial loss	3,171	1,706	440
Net periodic pension cost	$ 587	$ 2,038	$ 2,028