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
Comprehensive loss:
Net loss	$ (12,633)	$ (5,920)	$ (22,630)	$ (13,256)
Unrealized gain (loss) on investments available-for-sale	168	(36)	207	108
Comprehensive loss	$ (12,465)	$ (5,956)	$ (22,423)	$ (13,148)