Pension and Other Postretirement Benefits (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Pensions
Pension and other postretirement benefits expenses
Service cost	$ 1,633	$ 1,620	$ 4,912	$ 4,704
Interest cost	3,186	3,815	9,562	11,438
Expected return on plan assets	(6,963)	(7,594)	(20,897)	(22,391)
Amortization of prior service cost	83	128	248	281
Amortization of actuarial losses	3,999	3,502	12,005	10,148
Curtailment loss	0	0	0	484
Net periodic benefit cost	1,938	1,471	5,830	4,664
Other Postretirement Benefits
Pension and other postretirement benefits expenses
Service cost	27	20	77	61
Interest cost	203	259	615	780
Amortization of prior service cost	7	6	22	20
Amortization of actuarial losses	54	9	194	27
Net periodic benefit cost	$ 291	$ 294	$ 908	$ 888