Derivative Instruments - Additional Information (Detail) - USD ($)	Sep. 30, 2020	Dec. 31, 2019
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

Mark-to-market payable.

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Mark-to-market receivable.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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- Definition

Amount of right to receive cash collateral under master netting arrangements offset against derivative liabilities.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 45
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=117331979&loc=d3e41228-113958

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312

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- Definition

Fair value of securities pledged as collateral against derivative liabilities.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 12
-URI http://asc.fasb.org/extlink&oid=99393222&loc=SL20226013-175313

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The amount of cash or securities placed with a broker or counterparty as security for a trading or derivatives securities position which was partially obtained with funds provided by the broker dealer.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.8,17)
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

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