Statements of Comprehensive Loss Parentheticals (Parentheticals) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Stock-based compensation expense associated with research and development expense	$ 4,376	$ 3,673	$ 3,249
Stock-based compensation expense associated with general and administrative expense	$ 3,045	$ 2,822	$ 2,458