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Investments - Changes in Allowance for Credit Losses by Major Security Type of Investments Classified as Held-to-Maturity (Detail) $ in Thousands | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2024 USD ($) | Sep. 30, 2024 USD ($)
Debt Securities Held To Maturity Credit Quality Indicator [Line Items] |  |
Balance | $ 149 | $ 182
Provision for credit loss benefit | (13) | (46)
Balance | 136 | 136
Amortized cost | 436,505 | 436,505
AAA/AA/A Ratings [Member] |  |
Debt Securities Held To Maturity Credit Quality Indicator [Line Items] |  |
Amortized cost | 410,233 | 410,233
Baa/BBB Ratings [Member] |  |
Debt Securities Held To Maturity Credit Quality Indicator [Line Items] |  |
Amortized cost | 26,272 | 26,272
States and Political Subdivisions [Member] |  |
Debt Securities Held To Maturity Credit Quality Indicator [Line Items] |  |
Balance | 36 | 38
Provision for credit loss benefit | (1) | (3)
Balance | 35 | 35
Amortized cost | 387,702 | 387,702
States and Political Subdivisions [Member] | AAA/AA/A Ratings [Member] |  |
Debt Securities Held To Maturity Credit Quality Indicator [Line Items] |  |
Amortized cost | 385,526 | 385,526
States and Political Subdivisions [Member] | Baa/BBB Ratings [Member] |  |
Debt Securities Held To Maturity Credit Quality Indicator [Line Items] |  |
Amortized cost | 2,176 | 2,176
Corporate Bonds [Member] |  |
Debt Securities Held To Maturity Credit Quality Indicator [Line Items] |  |
Balance | 111 | 142
Provision for credit loss benefit | (11) | (42)
Balance | 100 | 100
Amortized cost | 37,453 | 37,453
Corporate Bonds [Member] | AAA/AA/A Ratings [Member] |  |
Debt Securities Held To Maturity Credit Quality Indicator [Line Items] |  |
Amortized cost | 13,367 | 13,367
Corporate Bonds [Member] | Baa/BBB Ratings [Member] |  |
Debt Securities Held To Maturity Credit Quality Indicator [Line Items] |  |
Amortized cost | 24,086 | 24,086
U.S. Agency-Based Mortgage-Backed Securities [Member] |  |
Debt Securities Held To Maturity Credit Quality Indicator [Line Items] |  |
Amortized cost | 2,877 | 2,877
U.S. Agency-Based Mortgage-Backed Securities [Member] | AAA/AA/A Ratings [Member] |  |
Debt Securities Held To Maturity Credit Quality Indicator [Line Items] |  |
Amortized cost | 2,877 | 2,877
U.S. Treasury Securities and Obligations of U.S. Government Agencies [Member] |  |
Debt Securities Held To Maturity Credit Quality Indicator [Line Items] |  |
Amortized cost | 8,456 | 8,456
U.S. Treasury Securities and Obligations of U.S. Government Agencies [Member] | AAA/AA/A Ratings [Member] |  |
Debt Securities Held To Maturity Credit Quality Indicator [Line Items] |  |
Amortized cost | 8,456 | 8,456
Asset-Backed Securities [Member] |  |
Debt Securities Held To Maturity Credit Quality Indicator [Line Items] |  |
Balance | 2 | 2
Provision for credit loss benefit | (1) | (1)
Balance | 1 | 1
Amortized cost | 17 | 17
Asset-Backed Securities [Member] | AAA/AA/A Ratings [Member] |  |
Debt Securities Held To Maturity Credit Quality Indicator [Line Items] |  |
Amortized cost | 7 | 7
Asset-Backed Securities [Member] | Baa/BBB Ratings [Member] |  |
Debt Securities Held To Maturity Credit Quality Indicator [Line Items] |  |
Amortized cost | $ 10 | $ 10

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- Definition Amount of allowance for credit loss for debt security measured at amortized cost (held-to-maturity). + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 320 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 5 -Subparagraph (aaa) -Publisher FASB -URI https://asc.fasb.org/1943274/2147481800/320-10-50-5 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 326 -SubTopic 20 -Name Accounting Standards Codification -Section 45 -Paragraph 1 -Publisher FASB -URI https://asc.fasb.org/1943274/2147479344/326-20-45-1 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Topic 326 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 13 -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org/1943274/2147479319/326-20-50-13 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Topic 326 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 13 -Subparagraph (f) -Publisher FASB -URI https://asc.fasb.org/1943274/2147479319/326-20-50-13 + Details
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