Employee Benefit Plans (Details 1) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Amounts recognized in the consolidated balance sheets
Employee benefit plan obligations	$ (26,716)	$ (35,026)
Pension Benefits
Amounts recognized in the consolidated balance sheets
Accrued expenses	(1,232)	(1,295)
Employee benefit plan obligations	(4,600)	(5,817)
Net amount recognized	(5,832)	(7,112)
Postretirement Benefits
Amounts recognized in the consolidated balance sheets
Accrued expenses	(1,098)	(1,148)
Employee benefit plan obligations	(21,504)	(28,609)
Net amount recognized	$ (22,602)	$ (29,757)