Comprehensive Income (Loss) Balance sheet classification (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Statement of Financial Position [Abstract]
Foreign currency translation	$ 1,431	$ 1,380
Derivative instruments designated as cash flow hedges	(10,259)	(10,352)
Postretirement medical plans	(742)	(742)
Accumulated other comprehensive loss	$ (9,570)	$ (9,714)