Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended			6 Months Ended	9 Months Ended	12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Jun. 30, 2014	Sep. 30, 2014	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Percent of pre-tax income:
U.S. federal statutory income tax rate (as a percent)						35.00%	35.00%	35.00%
State taxes, net of federal benefit (as a percent)						6.80%
Permanent items (as a percent)						2.30%	(2.20%)	(1.00%)
Research and development credit (as a percent)							2.70%	1.00%
Change in valuation allowance (as a percent)						(89.50%)	(35.50%)	(35.00%)
Effective income tax rate (as a percent)						(45.40%)	0.00%	0.00%
Current:
Federal						$ 29,505
State						11,440
Deferred:
Federal						(4,469)
Income tax expense	$ 512	$ 5,179	$ 30,785	$ 30,785	$ 35,964	36,476
Deferred tax assets (liabilities)
Deferred revenue	120,611					120,611	$ 16,667
License and technology payments	14,251					14,251	6,407
Share-based compensation	5,679					5,679	1,396
Accrued Expenses	442					442
Depreciation	(328)					(328)	(7)
Federal net operating loss carryforwards							30,084
State and local net operating loss carryforwards							5,026
Federal research and development credit carryforwards							2,966
State research and development credit carryforwards							1,483
Deferred income tax assets	140,655					140,655	64,022
Valuation allowance	(136,138)					(136,138)	$ (64,022)
Net deferred tax assets (liabilities)	$ 4,517					4,517
Increase to valuation allowance						$ 72,100