Statements of Comprehensive (Loss) Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statements of Comprehensive (Loss) Income
Net (loss) income	$ (39,440)	$ (25,918)	$ 91,570
Other comprehensive income (loss), net of tax:
Currency translation adjustment	12,580	(14,482)	(13,601)
Other comprehensive income (loss)	12,580	(14,482)	(13,601)
Comprehensive (loss) income	$ (26,860)	$ (40,400)	$ 77,969