Investments in Affiliates -Summary of Transactions in, and Earnings from, Investments in Affiliates (Excluding Affiliated Money Market Fund (Detail) - USD ($)	3 Months Ended			6 Months Ended
	Jun. 30, 2019		Jun. 30, 2018	Jun. 30, 2019		Jun. 30, 2018
Investments in and Advances to Affiliates [Line Items]
Beginning Value				$ 102,216,801
Change in Unrealized Appreciation (Depreciation)	$ 94,780		$ 127,812	102,303		$ 64,299
Ending Value	101,954,188			101,954,188
Affiliated Investments [Member]
Investments in and Advances to Affiliates [Line Items]
Beginning Value				102,216,801
Ending Value	101,954,188			101,954,188
Affiliated Investments [Member] | Exchange-Traded Fund [Member]
Investments in and Advances to Affiliates [Line Items]
Beginning Value	79,855,930		79,999,760	79,818,080	[1]	79,689,390
Change in Unrealized Appreciation (Depreciation)	79,485		325,510	117,335		635,880
Ending Value	79,935,415	[1]	$ 80,325,270	79,935,415	[1]	$ 80,325,270
Dividend Income	$ 478,954			$ 940,140

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