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Investment Securities - Additional Information (Detail) | 3 Months Ended | 9 Months Ended |
--- | --- | --- | ---
Sep. 30, 2023 USD ($) investmentSecurity securityLoan | Sep. 30, 2022 USD ($) | Sep. 30, 2023 USD ($) investmentSecurity securityLoan | Sep. 30, 2022 USD ($) | Dec. 31, 2022 USD ($)
Investment Securities [Line Items] |  |  |  |  |
Proceeds from the sale of investment securities | $ 0 | $ 0 | $ 24,200,000 | $ 0 |
Gross realized gain from the sale of investment securities |  |  | 200,000 |  |
Securities pledged as collateral | 585,000,000 |  | 585,000,000 |  | $ 595,800,000
Residential real estate mortgage-backed securities | 1,400,000,000 |  | $ 1,400,000,000 |  |
Life of mortgage-backed securities |  |  | 6 years 9 months 7 days |  |
Allowance for credit losses | 0 |  | $ 0 |  | 0
Obligations of U.S. government agencies |  |  |  |  |
Investment Securities [Line Items] |  |  |  |  |
Allowance for credit losses | $ 0 |  | $ 0 |  | 0
Number of available for sale securities in unrealized loss position (in investment securities) | investmentSecurity | 263 |  | 263 |  |
Percentage of aggregate depreciation in unrealized losses | 15.87% |  | 15.87% |  |
Obligations of states and political subdivisions |  |  |  |  |
Investment Securities [Line Items] |  |  |  |  |
Allowance for credit losses | $ 0 |  | $ 0 |  | 0
Number of available for sale securities in unrealized loss position (in investment securities) | investmentSecurity | 184 |  | 184 |  |
Percentage of aggregate depreciation in unrealized losses | 15.99% |  | 15.99% |  |
Corporate bonds |  |  |  |  |
Investment Securities [Line Items] |  |  |  |  |
Allowance for credit losses | $ 0 |  | $ 0 |  | 0
Number of available for sale securities in unrealized loss position (in investment securities) | investmentSecurity | 6 |  | 6 |  |
Percentage of aggregate depreciation in unrealized losses | 10.78% |  | 10.78% |  |
Asset backed securities |  |  |  |  |
Investment Securities [Line Items] |  |  |  |  |
Allowance for credit losses | $ 0 |  | $ 0 |  | 0
Number of available for sale securities in unrealized loss position (in investment securities) | investmentSecurity | 40 |  | 40 |  |
Percentage of aggregate depreciation in unrealized losses | 1.82% |  | 1.82% |  |
Non-agency collateralized mortgage obligations |  |  |  |  |
Investment Securities [Line Items] |  |  |  |  |
Allowance for credit losses | $ 0 |  | $ 0 |  | $ 0
Number of available for sale securities in unrealized loss position (in investment securities) | securityLoan | 24 |  | 24 |  |
Percentage of aggregate depreciation in unrealized losses | 11.85% |  | 11.85% |  |

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- Definition Investment Securities [Line Items] + References No definition available. + Details
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- Definition Life of mortgage backed securities. + References No definition available. + Details
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- Definition Amount of allowance for credit loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale). + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 320 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (aaa) -Publisher FASB -URI https://asc.fasb.org//1943274/2147481800/320-10-50-2 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 326 -SubTopic 30 -Name Accounting Standards Codification -Section 45 -Paragraph 1 -Publisher FASB -URI https://asc.fasb.org//1943274/2147479130/326-30-45-1 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Topic 326 -SubTopic 30 -Name Accounting Standards Codification -Section 50 -Paragraph 9 -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org//1943274/2147479106/326-30-50-9 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Topic 326 -SubTopic 30 -Name Accounting Standards Codification -Section 50 -Paragraph 9 -Subparagraph (i) -Publisher FASB -URI https://asc.fasb.org//1943274/2147479106/326-30-50-9 + Details
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- Definition Number of investments in debt securities measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in unrealized loss position, without allowance for credit loss. Includes beneficial interest in securitized financial asset. + References Reference 1: http://fasb.org/us-gaap/role/ref/otherTransitionRef -Topic 320 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 6 -Subparagraph (b)(3) -Publisher FASB -URI https://asc.fasb.org//1943274/2147481800/320-10-50-6 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 326 -SubTopic 30 -Name Accounting Standards Codification -Section 50 -Paragraph 4 -Subparagraph (b)(3) -Publisher FASB -URI https://asc.fasb.org//1943274/2147479106/326-30-50-4 + Details
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- Definition Debt securities issued by a United States government agency such as Government National Mortgage Association (Ginnie Mae), Federal Home Loan Mortgage Corporation (Freddie Mac), and Federal National Mortgage Association (Fannie Mae), which are short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify under that definition. Original maturity means original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three-years ago does not become a cash equivalent when its remaining maturity is three months. + References No definition available. + Details
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