Income Taxes - Deferred Tax Assets and Liabilities (Detail) - USD ($)	Dec. 31, 2016	Dec. 31, 2015
Deferred tax assets:
Net operating loss carryforwards	$ 49,627,652	$ 76,741,198
Accrued employee benefits	535,158	543,466
Research and development credit	9,367,227	6,962,731
Stock compensation	9,360,025	5,641,993
Federal AMT credit	1,062,451
Deferred rent	1,095,220	725,195
Deferred tax liabilities:
Depreciation	(44,732)	(6,062)
Net deferred tax asset	71,003,001	90,608,521
Valuation allowance	(71,003,001)	(90,608,521)
Net deferred tax asset	$ 0	$ 0