| Off-Balance Sheet Commitments - Allowance for Credit Losses Related to Off-Balance Sheet Items (Detail) - USD ($) $ in Thousands | 3 Months Ended | 9 Months Ended | ||
|---|---|---|---|---|
| Sep. 30, 2021 | Sep. 30, 2020 | Sep. 30, 2021 | Sep. 30, 2020 | |
| Loss Contingencies [Line Items] | ||||
| Balance at beginning of period | $ 3,643 | $ 6,347 | $ 2,792 | $ 2,397 | 
| Adjusted balance | 3,643 | 6,347 | 2,792 | 2,062 | 
| Provision expense (recovery) for credit losses | 1,208 | (658) | 2,059 | 3,627 | 
| Balance at end of period | $ 4,851 | $ 5,689 | $ 4,851 | 5,689 | 
| ASU 2016-13 | ||||
| Loss Contingencies [Line Items] | ||||
| Adjustment related to adoption of ASU 2016-13 | $ (335) | |||
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- Definition Off-balance sheet credit loss liability after adjustment. No definition available. 
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- Definition Off balance sheet credit loss liability effect of new accounting principle in period of adoption. No definition available. 
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- Definition 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. No definition available. 
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- Definition 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. Reference 1: http://www.xbrl.org/2003/role/disclosureRef 
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- Definition 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. Reference 1: http://www.xbrl.org/2003/role/disclosureRef 
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- Details 
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