Statements of Comprehensive Loss Parenthetical (Parenthetical) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Stock-based compensation expense associated with research and development expense	$ 797	$ 1,027	$ 3,195	$ 3,379
Stock-based compensation expense associated with general and administrative expense	$ 697	$ 723	$ 2,389	$ 2,349