Convertible Notes Payable - Schedule of Convertible Notes Payable (Detail) - USD ($)	Jun. 30, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Conversion payoff value	$ 2,014,472	$ 1,990,032
Discount on notes payable, current	(919,184)	(675,589)
Convertible notes payable, current (net of discount)	3,050,427	3,269,582
Ligand Note [Member] | Short Term Debt [Member]
Debt Instrument [Line Items]
Convertible note payable issued during 2014 to Ligand pursuant to the Master License Agreement with a 5% annual interest rate, due during 2016 (amended in January 2016 to a 2.5% annual interest rate with maturity extended to 2017, and subsequently amended in May 2017 with maturity extended to May 21, 2018)	$ 1,955,139	$ 1,955,139