Statements of Comprehensive Loss Parenthetical (Parenthetical) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Stock-based compensation expense associated with research and development expense	$ 915	$ 818	$ 1,952	$ 1,657
Stock-based compensation expense associated with general and administrative expense	$ 680	$ 632	$ 1,361	$ 1,265