Income Taxes (Details 2) - USD ($) $ in Thousands		1 Months Ended		12 Months Ended
	May. 19, 2014	Sep. 30, 2014	May. 31, 2014	Dec. 31, 2014	Dec. 31, 2013
Income taxes
Proceeds from the Novo Agreement				$ 83,333	$ 41,667
Income tax payments				40,200
Forecast | Minimum
Income taxes
Net operating losses				91,300
Novo A/S
Income taxes
Proceeds from the Novo Agreement				83,300
Novartis Pharma AG
Income taxes
Amount received			$ 200,000	$ 200,000
Patient enrollment-based milestone revenue achieved		$ 50,000
Novartis Pharma AG | Licensing and Commercialization Agreement
Income taxes
Amount received	$ 200,000
Novartis Pharma AG | Achievement of specified patient enrollment milestones | Licensing and Commercialization Agreement
Income taxes
Patient enrollment-based milestone revenue achieved		$ 50,000