Investments in Affiliates - Summary of Transactions in, and Earnings from, Investments in Affiliates (Excluding Affiliated Money Market Funds) (Detail) - USD ($)	3 Months Ended			9 Months Ended
	Sep. 30, 2019		Sep. 30, 2018	Sep. 30, 2019		Sep. 30, 2018
Investments In And Advances To Affiliates [Line Items]
Beginning Value				$ 395,084,923
Change in Unrealized Appreciation (Depreciation)	$ (255,940)		$ (516,239)	362,864		$ (256,277)
Ending Value	316,613,685			316,613,685
Affiliated Investments [Member]
Investments In And Advances To Affiliates [Line Items]
Beginning Value				395,084,923
Ending Value	316,613,685			316,613,685
Affiliated Investments [Member] | Invesco Treasury Collateral ETF [Member]
Investments In And Advances To Affiliates [Line Items]
Beginning Value	250,513,577		251,735,364	250,145,856	[1]	249,742,548
Change in Unrealized Appreciation (Depreciation)	(47,447)		(1,565,784)	320,274		427,032
Ending Value	250,466,130	[1]	250,169,580	250,466,130	[1]	250,169,580
Dividend Income	$ 1,383,536		$ 2,786,502	$ 4,329,886		$ 2,786,502

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