Investments in Affiliates -Summary of Transactions in, and Earnings from, Investments in Affiliates (Excluding Affiliated Money Market Fund (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2019		Dec. 31, 2018		Dec. 31, 2017
Investments in and Advances to Affiliates [Line Items]
Beginning Value	$ 102,216,801
Change in Unrealized Appreciation (Depreciation)	49,369		$ 45,626		$ (14,657)
Ending Value	105,630,007		102,216,801
Affiliated Investments [Member]
Investments in and Advances to Affiliates [Line Items]
Beginning Value	102,216,801
Ending Value	105,630,007		102,216,801
Affiliated Investments [Member] | Exchange-Traded Fund [Member]
Investments in and Advances to Affiliates [Line Items]
Beginning Value	79,818,080	[1]	79,689,390
Change in Unrealized Appreciation (Depreciation)	75,700		128,690
Ending Value	79,893,780	[1]	79,818,080	[1]	$ 79,689,390
Dividend Income	$ 1,780,629		$ 1,348,467

[1] Affiliated company. The security and the Fund are affiliated by having the same investment adviser. See Note 8.