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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 | 6 Months Ended
--- | --- | ---
Jun. 30, 2024 USD ($) | Jun. 30, 2024 USD ($)
Debt Securities Held To Maturity Credit Quality Indicator [Line Items] |  |
Balance | $ 165 | $ 182
Provision for credit loss benefit | (16) | (33)
Balance | 149 | 149
Amortized cost | 464,983 | 464,983
AAA/AA/A Ratings [Member] |  |
Debt Securities Held To Maturity Credit Quality Indicator [Line Items] |  |
Amortized cost | 432,776 | 432,776
Baa/BBB Ratings [Member] |  |
Debt Securities Held To Maturity Credit Quality Indicator [Line Items] |  |
Amortized cost | 32,207 | 32,207
States and Political Subdivisions [Member] |  |
Debt Securities Held To Maturity Credit Quality Indicator [Line Items] |  |
Balance | 37 | 38
Provision for credit loss benefit | (1) | (2)
Balance | 36 | 36
Amortized cost | 402,886 | 402,886
States and Political Subdivisions [Member] | AAA/AA/A Ratings [Member] |  |
Debt Securities Held To Maturity Credit Quality Indicator [Line Items] |  |
Amortized cost | 399,946 | 399,946
States and Political Subdivisions [Member] | Baa/BBB Ratings [Member] |  |
Debt Securities Held To Maturity Credit Quality Indicator [Line Items] |  |
Amortized cost | 2,940 | 2,940
Corporate Bonds [Member] |  |
Debt Securities Held To Maturity Credit Quality Indicator [Line Items] |  |
Balance | 126 | 142
Provision for credit loss benefit | (15) | (31)
Balance | 111 | 111
Amortized cost | 47,792 | 47,792
Corporate Bonds [Member] | AAA/AA/A Ratings [Member] |  |
Debt Securities Held To Maturity Credit Quality Indicator [Line Items] |  |
Amortized cost | 18,537 | 18,537
Corporate Bonds [Member] | Baa/BBB Ratings [Member] |  |
Debt Securities Held To Maturity Credit Quality Indicator [Line Items] |  |
Amortized cost | 29,255 | 29,255
U.S. Agency-Based Mortgage-Backed Securities [Member] |  |
Debt Securities Held To Maturity Credit Quality Indicator [Line Items] |  |
Amortized cost | 3,047 | 3,047
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 | 3,047 | 3,047
U.S. Treasury Securities and Obligations of U.S. Government Agencies [Member] |  |
Debt Securities Held To Maturity Credit Quality Indicator [Line Items] |  |
Amortized cost | 11,233 | 11,233
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 | 11,233 | 11,233
Asset-Backed Securities [Member] |  |
Debt Securities Held To Maturity Credit Quality Indicator [Line Items] |  |
Balance | 2 | 2
Balance | 2 | 2
Amortized cost | 25 | 25
Asset-Backed Securities [Member] | AAA/AA/A Ratings [Member] |  |
Debt Securities Held To Maturity Credit Quality Indicator [Line Items] |  |
Amortized cost | 13 | 13
Asset-Backed Securities [Member] | Baa/BBB Ratings [Member] |  |
Debt Securities Held To Maturity Credit Quality Indicator [Line Items] |  |
Amortized cost | $ 12 | $ 12

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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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