Income Taxes (Tables)

12 Months Ended

Dec. 31, 2016

Income Tax Disclosure [Abstract]

Schedule of effective income tax rate reconciliation

	December 31,
	2014		2015		2016
Income tax computed at federal statutory tax rate	34.0	%	34.0	%	34.0	%
State taxes, net of federal benefit	6.3	%	3.2	%	3.3	%
State taxes rate change, net of federal benefit	30.4	%	—		—
International operations	6.6	%	(4.8)	%	(0.7)	%
Research and development credits	(22.6)	%	3.8	%	4.0	%
Orphan drug credits	(57.4)	%	0.9	%	0.6	%
Equity compensation	16.6	%	(2.0)	%	(3.7)	%
Other	(2.1)	%	—		—
Change in valuation allowance	(11.8)	%	(35.1)	%	(37.5)	%
Total	—		—		—

Schedule of deferred tax assets and liabilities

	December 31,
	2015		2016
Deferred tax assets
Net operating loss carryforwards	$	73,678,000	$	78,021,000
Research and development credit carryforwards		12,398,000		14,143,000
Orphan drug credit		6,815,000		7,235,000
Stock options		5,568,000		7,105,000
Other		235,000		562,000
Deferred tax assets		98,694,000		107,066,000
Deferred tax liabilities
Deferred revenue		(8,049,000)		—
Property and equipment		(361,000)		(337,000)
Deferred tax liabilities	$	(8,410,000)	$	(337,000)
Net deferred tax asset before valuation allowance	$	90,284,000	$	106,729,000
Less valuation allowance		(90,284,000)		(106,729,000)
Net deferred tax assets	$	—	$	—

Schedule of unrecognized tax benefits

	Unrecognized Tax Positions
Balance at January 1, 2016	$	—
Additions based on tax positions related to the current year		3,405,000
Additions for tax positions of prior years		—
Reductions for tax positions of prior years		—
Settlements		—
Balance at December 31, 2016	$	3,405,000
Balance at December 31, 2016	$	3,405,000