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Comparative Data for the Two Months Ended December 31, 2017 (Unaudited) - Comparative Data for Statements of Comprehensive Income (Parenthetical) (Detail) - $ / shares
2 Months Ended 3 Months Ended 12 Months Ended
Dec. 31, 2018
[1]
Dec. 31, 2017
Oct. 31, 2018
[1]
Jul. 31, 2018
[1]
Apr. 30, 2018
[1]
Jan. 31, 2018
[1]
Oct. 31, 2017
[1]
Jul. 31, 2017
[1]
Apr. 30, 2017
[1]
Jan. 31, 2017
[1]
Oct. 31, 2018
Oct. 31, 2017
Condensed Financial Statements, Captions [Line Items]                        
Basic and Diluted Earnings per Share $ 0.09 $ 0.00 [2] $ 0.11 $ 0.08 $ 0.04 $ 0.02 $ 0.01 $ (0.06) $ (0.06) $ (0.07) $ 0.26 $ (0.18)
Maximum [Member]                        
Condensed Financial Statements, Captions [Line Items]                        
Basic and Diluted Earnings per Share   $ 0.01                    
[1] The amount shown for a Share outstanding for quarterly statements may not correlate with year to date amounts due to timing of subscriptions and redemptions in relation to income earned or distributed.
[2] Less than $0.01 per Share