Investments in Affiliates - Summary of Transactions in, and Earnings from, Investments in Affiliates (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Investments In And Advances To Affiliates [Line Items]
Beginning Value			$ 21,851,133
Change in Unrealized Appreciation (Depreciation)	$ 1,578	$ 662	(2,987)	$ 10,241
Ending Value	40,676,310		40,676,310
Affiliated Investments [Member]
Investments In And Advances To Affiliates [Line Items]
Beginning Value	30,524,380		21,851,133
Purchases at Cost	87,140,114		135,497,908
Proceeds from Sales	(76,988,184)		(116,672,731)
Ending Value	40,676,310		40,676,310
Dividend Income	2,503		56,300
Affiliated Investments [Member] | Money Market Mutual Fund - Invesco Premier U.S. Government Money Portfolio - Institutional Class [Member]
Investments In And Advances To Affiliates [Line Items]
Beginning Value	30,524,380	6,143,756	21,851,133	1,793,677
Purchases at Cost	45,820,678	27,895,488	94,178,472	66,360,923
Proceeds from Sales	(76,345,058)	(32,475,857)	(116,029,605)	(66,591,213)
Ending Value		1,563,387		1,563,387
Dividend Income	2,376	$ 15,189	56,173	$ 38,357
Affiliated Investments [Member] | Money Market Mutual Fund - Invesco Government and Agency Portfolio - Institutional Class [Member]
Investments In And Advances To Affiliates [Line Items]
Purchases at Cost	41,319,436		41,319,436
Proceeds from Sales	(643,126)		(643,126)
Ending Value	40,676,310		40,676,310
Dividend Income	$ 127		$ 127