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	$ (2,523)	$ (300)	$ (6,201)	$ (6,883)
Unrealized (loss) gain on available-for-sale and long-term marketable securities:
Unrealized (loss) gain arising during holding period, net of tax expense of $7 and $0 for three months ended September 30, 2016 and 2015, respectively, and tax benefit of $56 and $0 for nine months ended September 30, 2016 and 2015, respectively	(22)	98	121	123
Other comprehensive (loss) gain	(22)	98	121	123
Total comprehensive loss	$ (2,545)	$ (202)	$ (6,080)	$ (6,760)