Income Taxes (Details) (USD $)	12 Months Ended
	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)	(66.40%)	(35.50%)	(35.00%)
Effective income tax rate (as a percent)	(22.30%)	0.00%	0.00%
Current:
Federal	$ 29,505,000
State	11,440,000
Deferred:
Federal	(23,053,000)
Income tax expense	17,892,000
Deferred tax assets (liabilities)
Deferred revenue	120,611,000	16,667,000
License and technology payments	14,251,000	6,407,000
Share-based compensation	5,679,000	1,396,000
Accrued Expenses	442,000
Depreciation	(328,000)	(7,000)
Federal net operating loss carryforwards		30,084,000
State and local net operating loss carryforwards		5,026,000
Federal research and development credit carryforwards		2,966,000
State research and development credit carryforwards		1,483,000
Deferred income tax assets	140,655,000	64,022,000
Valuation allowance	(117,554,000)	(64,022,000)
Net deferred tax assets (liabilities)	23,101,000
Increase to valuation allowance	$ 53,600,000