Statements of Comprehensive Loss Parenthetical (Parenthetical) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Stock-based compensation expense associated with research and development expense	$ 923	$ 823	$ 2,875	$ 2,480
Stock-based compensation expense associated with general and administrative expense	$ 669	$ 609	$ 2,030	$ 1,874