Income Taxes (Tables)

12 Months Ended

Dec. 31, 2017

Schedule of Components of Loss Before Income Taxes and Reconciliation of Statutory Federal Income Tax Rate to Provision for Income Taxes

The U.S. components of loss before income taxes and a reconciliation of the statutory federal income rate to with the provision for income taxes follow:

	Year ended December 31,
	2017			2016			2015
Federal tax at statutory rate		34.0	%		34.0	%		34.0	%
State and local tax at statutory rate		3.8			1.4			3.0
Research and development tax credits		11.9			6.4			0.4
Equity compensation		(0.6	)		(0.2	)		(0.6	)
Alternative minimum tax		(1.3	)		—			—
Change in valuation allowance		6.9			(41.6	)		(36.8	)
Impact of US tax reform		(54.7	)		—			—
Effective tax rate		0.0	%		0.0	%		0.0	%

Schedule of Significant Deferred Tax Assets and Liabilities

Significant components of the Company’s deferred tax assets and liabilities are as follows:

		December 31,
		2017			2016
	(in thousands)
Deferred tax assets:
Accrued expenses		$	4,305		$	2,170
Deferred revenue			32,093			12,157
Intangible assets			509			449
Restricted stock			—			45
Non-qualified stock options			3,129			2,963
Research and development credits			25,322			10,510
Net operating loss carryforward			42,335			84,372
Other			600			326
Total deferred tax assets			108,293			112,992
Less valuation allowance			(108,112	)		(112,986	)
Total deferred tax assets, net of valuation allowance			181			6
Deferred tax liabilities:
Fixed assets			(181	)		(6	)
Total deferred tax liabilities			(181	)		(6	)
Net deferred tax asset		$	—		$	—