Consolidated Statements of Comprehensive Loss (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (8,620)	$ (5,513)	$ (15,848)	$ (10,144)
Other comprehensive loss:
Unrealized loss on available-for-sale securities	(3)	(7)	(2)	(25)
Comprehensive loss	$ (8,623)	$ (5,520)	$ (15,850)	$ (10,169)