Pension and Other Postretirement Benefits (Details 10) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Pensions [Member]
Pension and other postretirement benefits expenses
Service cost	$ 6,269	$ 5,425	$ 5,961
Interest cost	15,084	18,239	17,383
Expected return on plan assets	(29,698)	(29,425)	(29,900)
Amortization of prior service cost	359	404	560
Recognized losses	13,626	8,889	11,628
Curtailment loss	484	0	0
Settlement loss	549	340	0
Net periodic benefit cost	6,673	3,872	5,632
Other Postretirement Benefits [Member]
Pension and other postretirement benefits expenses
Service cost	81	70	85
Interest cost	1,041	1,345	1,358
Expected return on plan assets	0	0	0
Amortization of prior service cost	27	25	20
Recognized losses	35	13	561
Curtailment loss	0	0	0
Settlement loss	0	0	0
Net periodic benefit cost	$ 1,184	$ 1,453	$ 2,024