Subsequent Events (Details) (USD $)	0 Months Ended	12 Months Ended			84 Months Ended	0 Months Ended
	Sep. 30, 2013	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2013	Feb. 18, 2014 Subsequent event	Jan. 23, 2014 Subsequent event Novo A/S Royalty agreement
Subsequent events
Cash proceeds received in exchange for a low single-digit royalty interest		$ 41,667,000			$ 41,667,000		$ 41,700,000
Third potential financing tranche							41,700,000
Shares of common stock offered in follow on offering						2,628,571
Offering price (in dollars per share)						$ 31.50
Shares sold by the company in follow on offering	8,740,000					1,900,000
Shares sold by selling stockholders in follow on offering						728,571
Shares sold by selling stockholders upon full exercise by underwriters of their option to purchase additional shares						342,857
Net proceeds, after deducting underwriters' commissions and other offering expense		$ 94,000	$ 2,000	$ 4,000	$ 218,000	$ 55,500,000