Pension and Other Postretirement Benefits (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended		6 Months Ended
	Mar. 31, 2016	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Pensions [Member]
Pension and other postretirement benefits expenses
Service cost		$ 1,318	$ 1,299	$ 2,702	$ 2,752
Interest cost		4,945	5,297	9,781	9,992
Expected return on plan assets		(7,667)	(8,589)	(15,210)	(16,159)
Amortization of prior service cost (credit)		55	77	105	155
Amortization of actuarial losses		2,856	4,056	5,412	7,485
Net periodic benefit cost		1,507	2,140	2,790	4,225
Other Postretirement Benefits [Member]
Pension and other postretirement benefits expenses
Service cost		27	36	61	73
Interest cost		431	425	884	918
Amortization of prior service cost (credit)		(94)	(141)	(187)	(282)
Amortization of actuarial losses		91	244	267	505
Net periodic benefit cost		$ 455	$ 564	$ 1,025	$ 1,214
United States Pension Plan of US Entity [Member]
Pension and other postretirement benefits expenses
Discretionary contributions	$ 15,000