Income Taxes (Tables)

12 Months Ended

Dec. 31, 2015

Income Taxes

Schedule of components of the net deferred tax asset

	December 31,
	2014		2015
Gross deferred tax assets:
Net operating loss carryovers	$	43,399,282	$	47,179,913
Stock compensation		2,222,537		4,455,016
R&D credit		3,598,910		5,004,252
Capitalized costs		—		5,155,127
Other		640,548		201,865
Total gross deferred tax assets		49,861,277		61,996,173
Gross deferred tax liabilities:
Depreciation		(28,069)		—
Conversion option discount		(6,079,535)		(4,217,175)
Indefinite-lived intangible asset		(16,879,659)		(16,879,659)
Total gross deferred tax liabilities		(22,987,263)		(21,096,834)
Net deferred tax assets		26,874,014		40,899,339
Less: valuation allowance		(43,753,673)		(57,778,998)
Net deferred tax liabilities after valuation allowance	$	(16,879,659)	$	(16,879,659)

Schedule of reconciliation of income tax expense (benefit) at the statutory federal income tax rate and income taxes

	Year Ended
	December 31,
	2014		2015
Federal income tax expense at statutory rate	34.0	%	34.0	%
Permanent items	(1.9)		(3.3)
State income tax, net of federal benefit	6.4		5.8
Effect of rates different than statutory	—		(7.6)
Adjustment to NOL and credit carryforwards	(16.3)		—
Tax credits generated	2.0		1.9
Change in valuation allowance	(24.2)		(30.8)
Effective income tax rate	—	%	—	%