Employee Benefits Plans (Details 10) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Amortization of:
Postretirement benefit income	$ 61,215	$ 41,704	$ 138,656
Other Postretirement Benefits
Other Postretirement benefit expense
Service cost	215	363	446
Interest cost	906	1,097	1,421
Amortization of:
Net actuarial gain	(1,989)	(1,773)	(725)
Prior service loss (credit)	(231)	(1,083)	(2,459)
Postretirement benefit income	(1,099)	(1,396)	(1,317)
Other Postretirement benefit expense U.S.
Amortization of:
Postretirement benefit income	(1,429)	(1,887)	(1,839)
Other Postretirement benefit expense Foreign
Amortization of:
Postretirement benefit income	$ 330	$ 491	$ 522