CONDENSED STATEMENTS OF COMPREHENSIVE LOSS (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
CONDENSED STATEMENTS OF COMPREHENSIVE LOSS
Net loss	$ (8,440)	$ (11,897)
Net unrealized loss on marketable securities	(76)	(22)
Comprehensive loss	$ (8,516)	$ (11,919)