Fair Value of Financial Assets - Schedule of Assets Measured at Fair Value on Recurring Basis (Detail) - USD ($)	Dec. 31, 2016	Dec. 31, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities	$ 174,688,468	$ 48,302,507
Fair Value Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	9,830,127	61,533,797
Marketable securities	179,413,509	55,659,930
Assets, Total	189,243,636	117,193,727
Level 2 [Member] | Fair Value Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	9,830,127	61,533,797
Marketable securities	179,413,509	55,659,930
Assets, Total	$ 189,243,636	$ 117,193,727