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Income Taxes - Reconciliation of Reported Estimated Income Tax Benefit (Detail) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Income Tax Disclosure [Abstract]
United States federal tax at statutory rate	$ (91,293)	$ 2,926,615	$ 2,350,992
State taxes (net of federal benefit)	609,476	1,460,289	1,480,185
Deferred income tax adjustments	(855,130)	(512,375)
Deferred state blended rate adjustments	(344,178)
Research credit, net	(225,605)
Orphan drug credit, net	(843,463)	(4,895,671)	(7,056,607)
Other permanent items	2,931	7,627	4,696
Equity- based compensation	241,467	279,165	725,811
Fair value adjustment of preferred stock warrant liability	218,872	(52,743)	(496,208)
Change in valuation allowance	1,286,923	787,093	2,991,131
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