Pension and Other Postretirement Benefits (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended		9 Months Ended
	Mar. 31, 2016	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Pensions [Member]
Pension and other postretirement benefits expenses
Service cost		$ 1,354	$ 1,374	$ 4,056	$ 4,126
Interest cost		4,869	4,976	14,650	14,968
Expected return on plan assets		(7,564)	(8,048)	(22,774)	(24,207)
Amortization of prior service cost (credit)		52	76	157	231
Amortization of actuarial losses		2,697	3,730	8,109	11,215
Net periodic benefit cost		1,408	2,108	4,198	6,333
Other Postretirement Benefits [Member]
Pension and other postretirement benefits expenses
Service cost		31	36	92	109
Interest cost		440	459	1,324	1,377
Amortization of prior service cost (credit)		(93)	(141)	(280)	(423)
Amortization of actuarial losses		134	253	401	758
Net periodic benefit cost		$ 512	$ 607	$ 1,537	$ 1,821
United States Pension Plan of US Entity [Member]
Pension and other postretirement benefits expenses
Discretionary contributions	$ 15,000