Income Taxes - Summary of Net Deferred Tax Asset (Detail) - USD ($)	Dec. 31, 2016	Dec. 31, 2015
Deferred tax asset:
Net operating loss carryforwards	$ 42,436,541	$ 42,315,384
Deferred compensation	1,681,158	1,474,625
Depreciation and amortization	842,073	1,010,636
Research and development credits	3,788,955	3,788,752
Accrued expenses	391,365	314,633
Impairment loss	730,831	850,334
Other	438,039	248,933
Total deferred tax assets	50,308,962	50,003,297
Less: Valuation allowance	(50,308,962)	(50,003,297)
Net deferred tax asset	$ 0	$ 0