Carrying Amounts and Fair Values of Company's Financial Instruments (Detail) - USD ($)		Sep. 30, 2018	Dec. 31, 2017
Assets
Assets, Fair Value Disclosure		$ 89,366,906	$ 42,374,500
Fair Value, Inputs, Level 1 [Member]
Assets
Assets, Fair Value Disclosure		89,366,906	42,374,500
Fair Value, Inputs, Level 2 [Member]
Assets
Assets, Fair Value Disclosure		0	0
Fair Value, Inputs, Level 3 [Member]
Assets
Assets, Fair Value Disclosure		0	0
Money Market Funds [Member]
Assets
Assets, Fair Value Disclosure	[1]	87,479,604	41,231,405
Money Market Funds [Member] | Fair Value, Inputs, Level 1 [Member]
Assets
Assets, Fair Value Disclosure	[1]	87,479,604	41,231,405
Money Market Funds [Member] | Fair Value, Inputs, Level 2 [Member]
Assets
Assets, Fair Value Disclosure	[1]	0	0
Money Market Funds [Member] | Fair Value, Inputs, Level 3 [Member]
Assets
Assets, Fair Value Disclosure	[1]	0	0
Marketable securities – certificates of deposit [Member]
Assets
Assets, Fair Value Disclosure		1,811,515	1,057,090
Marketable securities – certificates of deposit [Member] | Fair Value, Inputs, Level 1 [Member]
Assets
Assets, Fair Value Disclosure		1,811,515	1,057,090
Marketable securities – certificates of deposit [Member] | Fair Value, Inputs, Level 2 [Member]
Assets
Assets, Fair Value Disclosure		0	0
Marketable securities – certificates of deposit [Member] | Fair Value, Inputs, Level 3 [Member]
Assets
Assets, Fair Value Disclosure		0	0
Marketable securities – equity securities [Member]
Assets
Assets, Fair Value Disclosure		75,787	86,005
Marketable securities – equity securities [Member] | Fair Value, Inputs, Level 1 [Member]
Assets
Assets, Fair Value Disclosure		75,787	86,005
Marketable securities – equity securities [Member] | Fair Value, Inputs, Level 2 [Member]
Assets
Assets, Fair Value Disclosure		0	0
Marketable securities – equity securities [Member] | Fair Value, Inputs, Level 3 [Member]
Assets
Assets, Fair Value Disclosure		$ 0	$ 0

[1] Included in cash and cash equivalents