Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Comprehensive Income [Abstract]
Net income	$ 10,172	$ 8,398	$ 6,789	$ 4,978	$ 24,131	$ (441)	$ 3,115	$ 2,802	$ 30,337	$ 29,607	$ 21,984
Other comprehensive income (loss)
Foreign currency translation adjustment									1,725	(2,078)	(2,756)
Deferred gain on available for sale securities, net of tax									834	413	17
Current period cash flow hedging activity, net of $941 tax expense in 2017, $73 tax benefit in 2016 and $357 tax benefit in 2015									1,543	(252)	(577)
Reclassification of hedging activities into earnings, net of $1,255 tax expense in 2017, $419 tax benefit in 2016 and $191 tax benefit in 2015									(2,369)	757	409
Current period pension and postretirement plan adjustment, net of $440 tax expense in 2017, $1,098 tax benefit in 2016 and $1,222 tax benefit in 2015									749	(2,011)	(1,204)
Reclassification of pension and postretirement adjustments into earnings, net of $363 tax benefit in 2017, $408 tax benefit in 2016 and $420 tax benefit in 2015									582	688	856
Total other comprehensive income (loss)									3,064	(2,483)	(3,255)
Comprehensive income									$ 33,401	$ 27,124	$ 18,729