Condensed Consolidated Statements of Comprehensive Loss (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (7,545)	$ (6,145)	$ (22,098)	$ (18,480)
Changes in unrealized gain on available-for-sale securities	20	27	41
Comprehensive loss	$ (7,525)	$ (6,118)	$ (22,057)	$ (18,480)