Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (10,670)	$ (10,068)
Other comprehensive income:
Net unrealized income (loss) on marketable securities	(18)	11
Total comprehensive loss	$ (10,688)	$ (10,057)