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Commitments, Contingencies and Guarantees - Additional Information (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Jun. 30, 2021	Dec. 31, 2020	Jun. 30, 2020	Dec. 31, 2019
Commitments and Contingencies Disclosure [Line Items]
ACL for off-balance sheet credit exposures	$ 2,588,000	$ 6,478,000	$ 2,588,000	$ 6,478,000	$ 3,588,000	$ 5,588,000	$ 6,478,000	$ 2,978,000
Provision for off-balance sheet credit exposures	(1,000,000)		(3,000,000)	3,500,000
Accrued Expenses and Taxes [Member]
Commitments and Contingencies Disclosure [Line Items]
ACL for off-balance sheet credit exposures	2,600,000		2,600,000			$ 5,600,000
Provision for Credit Losses [Member]
Commitments and Contingencies Disclosure [Line Items]
Provision for off-balance sheet credit exposures	$ (1,000,000.0)	$ 0	$ (3,000,000.0)	$ 3,500,000

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Commitments and contingencies disclosure.

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Amount of expected credit loss for credit exposure on off-balance-sheet commitment, including but not limited to, loan commitment, standby letter of credit, financial guarantee not accounted for as insurance. Excludes off-balance sheet credit exposure accounted for as insurance and instrument accounted for under derivatives and hedging.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 460
-SubTopic 10
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=121611286&loc=d3e11927-110247

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=124255206&loc=SL82919202-210446

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Amount of expense (reversal of expense) for expected credit loss for off-balance sheet credit exposure. Excludes off-balance sheet credit exposure accounted for as insurance and instrument accounted for under derivatives and hedging.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 13
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=124255953&loc=SL82919249-210447

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