Basis of Presentation (Details) (USD $)	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Basis of Presentation
Cash, cash equivalents and marketable securities	$ 274,200,000
Net Loss	(29,903,000)	(17,332,000)
Net cash used in operations	$ (31,875,000)	$ (17,200,000)