Condensed Consolidated Statements of Comprehensive Loss (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (7,700)	$ (4,666)	$ (20,454)	$ (11,847)
Unrealized gain on short-term investments	5		5
Comprehensive loss	$ (7,695)	$ (4,666)	$ (20,449)	$ (11,847)