Pension and Other Postretirement Benefits (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2016	Mar. 31, 2015
Pensions [Member]
Pension and other postretirement benefits expenses
Service cost		$ 1,384	$ 1,453
Interest cost		4,836	4,695
Expected return on plan assets		(7,543)	(7,570)
Amortization of prior service cost (credit)		50	78
Amortization of actuarial losses		2,556	3,429
Net periodic benefit cost		1,283	2,085
Other Postretirement Benefits [Member]
Pension and other postretirement benefits expenses
Service cost		34	37
Interest cost		453	493
Amortization of prior service cost (credit)		(93)	(141)
Amortization of actuarial losses		176	261
Net periodic benefit cost		$ 570	$ 650
United States Pension Plan of US Entity [Member]
Pension and other postretirement benefits expenses
Discretionary contributions	$ 15,000