Statements of Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (9,238)	$ (16,492)	$ (31,238)
Unrealized gain (loss) on available-for-sale and long-term marketable securities:
Unrealized gain (loss) arising during holding period, net of tax	52	(23)	(236)
Other comprehensive gain (loss)	52	(23)	(236)
Total comprehensive loss	$ (9,186)	$ (16,515)	$ (31,474)