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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 $ 57,894,114  
Change in Unrealized Appreciation (Depreciation) 1,527 $ 1,855
Ending Value 21,406,990  
Affiliated Investments [Member]    
Investments In And Advances To Affiliates [Line Items]    
Beginning Value 57,894,114  
Ending Value 21,406,990  
Affiliated Investments [Member] | Exchange-Traded Fund [Member]    
Investments In And Advances To Affiliates [Line Items]    
Beginning Value 16,031,526 [1] 16,016,336
Change in Unrealized Appreciation (Depreciation) 98,735 7,595
Ending Value 16,130,261 [1] 16,023,931
Dividend Income $ 66,819 $ 92,542
[1] Affiliated company. The security and the Fund are affiliated by having the same investment adviser. See Note 8.