Pension and Other Postretirement Benefits (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Pensions [Member]
Pension and other postretirement benefits expenses
Service cost	$ 1,643	$ 1,384
Interest cost	4,621	4,836
Expected return on plan assets	(6,860)	(7,543)
Amortization of prior service cost (credit)	109	50
Amortization of actuarial losses	2,480	2,556
Settlement gain	(261)	0
Net periodic benefit cost	1,732	1,283
Expected company contributions in 2017	20,000
Other Postretirement Benefits [Member]
Pension and other postretirement benefits expenses
Service cost	22	34
Interest cost	389	453
Amortization of prior service cost (credit)	(17)	(93)
Amortization of actuarial losses	69	176
Net periodic benefit cost	463	$ 570
U.S. Qualified Pension Plan [Member]
Pension and other postretirement benefits expenses
Expected company contributions in 2017	$ 15,000