Hedging - Changes to Comprehensive Income (Loss) Associated with the Company's Hedging Activities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Beginning balance of unrealized loss on forward exchange contracts	$ (527)		$ (819)
Other comprehensive loss before reclassifications	83	$ 589	694
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	433	881	627
Other comprehensive income (loss)	350	292	$ (67)
Ending balance of unrealized loss on forward exchange contracts	$ (177)	$ (527)