Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Components of comprehensive income
Net income	$ 3,920	$ 6,081	$ 3,687	$ 4,066	$ 2,286	$ 5,676	$ 2,559	$ 2,365	$ 17,754	$ 12,886	$ 19,367
Minimum pension liability adjustments										946	(127)
Mark to market of foreign exchange hedges									(352)
Reclassification to interest expense										678	921
Mark to market of interest rate hedges										(15)	(49)
Deferred income tax credit (expense)									129	(585)	(271)
Comprehensive (loss) income									$ 17,531	$ 13,910	$ 19,841