Fair Value Measurements - Schedule of Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($)		Jun. 30, 2018	Dec. 31, 2017
Assets:
Total assets at fair value		$ 36,250,402	$ 41,967,314
Money Market Funds [Member]
Assets:
Total assets at fair value	[1]	2,177,681	1,043,852
Reverse Repurchase Agreements [Member]
Assets:
Total assets at fair value	[2]	17,000,000	18,000,000
U.S. Government Agencies Securities [Member]
Assets:
Total assets at fair value	[2]	17,072,720	22,923,462
Level 1 [Member]
Assets:
Total assets at fair value		2,177,681	1,043,852
Level 1 [Member] | Money Market Funds [Member]
Assets:
Total assets at fair value	[1]	2,177,681	1,043,852
Level 2 [Member]
Assets:
Total assets at fair value		34,072,720	40,923,462
Level 2 [Member] | Reverse Repurchase Agreements [Member]
Assets:
Total assets at fair value	[2]	17,000,000	18,000,000
Level 2 [Member] | U.S. Government Agencies Securities [Member]
Assets:
Total assets at fair value	[2]	$ 17,072,720	$ 22,923,462

[1] Money market funds included in cash and cash equivalents in the consolidated balance sheets, are valued at quoted market prices in active markets.

[2] U.S. Reverse repurchase agreements and U.S. government agency securities are recorded at fair market values, which are determined based on the most recent observable inputs for similar instruments in active markets or quoted prices for identical or similar instruments in markets that are not active or are directly or indirectly observable.