Investments in Affiliates - Summary of Transactions in, and Earnings from, Investments in Affiliates (Excluding Affiliated Money Market Funds) (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2020		Mar. 31, 2019
Investments In And Advances To Affiliates [Line Items]
Beginning Value	$ 767,882,587
Change in Unrealized Appreciation (Depreciation)	134,500		$ 117,402
Ending Value	284,958,450
Affiliated Investments [Member]
Investments In And Advances To Affiliates [Line Items]
Beginning Value	767,882,587
Ending Value	284,958,450
Affiliated Investments [Member] | Invesco Treasury Collateral ETF [Member]
Investments In And Advances To Affiliates [Line Items]
Beginning Value	250,383,096	[1]	250,145,856
Change in Unrealized Appreciation (Depreciation)	1,542,060		118,620
Ending Value	251,925,156	[1]	250,264,476
Dividend Income	$ 1,043,595		$ 1,445,333

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