Statements of Comprehensive Loss Parentheticals (Parentheticals) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Stock-based compensation expense associated with research and development expense	$ 3,693	$ 4,020	$ 4,376
Stock-based compensation expense associated with general and administrative expense	$ 3,150	$ 3,061	$ 3,045