Consolidated Statements of Comprehensive Loss (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (42,613)	$ (41,257)	$ (38,841)
Other comprehensive (loss) income:
Change in unrealized gain on available-for-sale securities, net	(33)	20	11
Other comprehensive (loss) income, net	(33)	20	11
Comprehensive loss	$ (42,646)	$ (41,237)	$ (38,830)