Unaudited Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Statement of Comprehensive Income [Abstract]
Net loss	$ (12,683)	$ (5,737)	$ (27,729)	$ (17,400)
Other comprehensive income (loss):
Unrealized income (loss) on short-term investments, net of tax	19	(10)	11	(10)
Unrealized income (loss) on derivative instruments, net of tax	(884)	493	(2,985)	2,617
Total other comprehensive income (loss)	(865)	483	(2,974)	2,607
Comprehensive loss	$ (13,548)	$ (5,254)	$ (30,703)	$ (14,793)