Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (10,515)	$ (13,552)	$ (31,733)	$ (35,802)
Other comprehensive loss:
Foreign currency translation adjustment	(21)	(10)	109	(162)
Changes in unrealized gain (loss) on investments, net of income taxes of $(36) and $136 for the three and nine months ended September 30, 2016 and $0 for the three and nine months ended September 30, 2015	(108)	(77)	163	(237)
Comprehensive loss	$ (10,644)	$ (13,639)	$ (31,461)	$ (36,201)