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Derivative Instruments - Additional Information (Detail) - USD ($) | Sep. 30, 2020 | Dec. 31, 2019
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Trading Futures Contracts |  |
Derivative Instruments and Hedging Activities Disclosures [Line Items] |  |
Initial margin in securities | $ 600,000 | $ 3,000,000.0
Mark-to-market receivable |  | 300,000
Trading Futures Contracts | Maximum |  |
Derivative Instruments and Hedging Activities Disclosures [Line Items] |  |
Mark-to-market payable | 100,000 |
Other Assets |  |
Derivative Instruments and Hedging Activities Disclosures [Line Items] |  |
Funds needed to post execute swap transaction | 3,000,000.0 | 3,000,000.0
Other Assets | Interest Rate Swap |  |
Derivative Instruments and Hedging Activities Disclosures [Line Items] |  |
Margin calls made in connection with interest rate swaps | $ 18,600,000 | $ 12,500,000

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