Carrying Amounts and Fair Values of Company's Financial Instruments (Detail) - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Assets
Assets, Fair Value Disclosure	$ 42,374,500	$ 48,944,580
Fair Value, Inputs, Level 1 [Member]
Assets
Assets, Fair Value Disclosure	42,374,500	43,605,694
Fair Value, Inputs, Level 2 [Member]
Assets
Assets, Fair Value Disclosure	0	0
Fair Value, Inputs, Level 3 [Member]
Assets
Assets, Fair Value Disclosure		5,338,886
Money Market Funds [Member]
Assets
Assets, Fair Value Disclosure	41,231,405	42,553,887
Money Market Funds [Member] | Fair Value, Inputs, Level 1 [Member]
Assets
Assets, Fair Value Disclosure	41,231,405	42,553,887
Money Market Funds [Member] | Fair Value, Inputs, Level 2 [Member]
Assets
Assets, Fair Value Disclosure	0	0
Money Market Funds [Member] | Fair Value, Inputs, Level 3 [Member]
Assets
Assets, Fair Value Disclosure	0	0
Certificates of Deposit [Member]
Assets
Assets, Fair Value Disclosure	1,057,090	1,051,807
Certificates of Deposit [Member] | Fair Value, Inputs, Level 1 [Member]
Assets
Assets, Fair Value Disclosure	1,057,090	1,051,807
Certificates of Deposit [Member] | Fair Value, Inputs, Level 2 [Member]
Assets
Assets, Fair Value Disclosure	0	0
Certificates of Deposit [Member] | Fair Value, Inputs, Level 3 [Member]
Assets
Assets, Fair Value Disclosure	0	0
Equity Securities [Member]
Assets
Assets, Fair Value Disclosure	86,005	5,338,886
Equity Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Assets
Assets, Fair Value Disclosure	86,005	0
Equity Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Assets
Assets, Fair Value Disclosure	0	0
Equity Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Assets
Assets, Fair Value Disclosure	$ 0	$ 5,338,886