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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, 2022 USD ($) | Jun. 30, 2022 USD ($)
Debt Securities Held To Maturity Credit Quality Indicator [Line Items] |  |
Balance | $ 290 | $ 195
Provision for credit loss expense (benefit) | (14) | 81
Balance | 276 | 276
Amortized cost | 541,573 | 541,573
AAA/AA/A Ratings [Member] |  |
Debt Securities Held To Maturity Credit Quality Indicator [Line Items] |  |
Amortized cost | 499,142 | 499,142
Baa/BBB Ratings [Member] |  |
Debt Securities Held To Maturity Credit Quality Indicator [Line Items] |  |
Amortized cost | 42,416 | 42,416
B Ratings [Member] |  |
Debt Securities Held To Maturity Credit Quality Indicator [Line Items] |  |
Amortized cost | 15 | 15
States and Political Subdivisions [Member] |  |
Debt Securities Held To Maturity Credit Quality Indicator [Line Items] |  |
Balance | 45 | 48
Provision for credit loss expense (benefit) | (1) | (4)
Balance | 44 | 44
Amortized cost | 453,781 | 453,781
States and Political Subdivisions [Member] | AAA/AA/A Ratings [Member] |  |
Debt Securities Held To Maturity Credit Quality Indicator [Line Items] |  |
Amortized cost | 450,801 | 450,801
States and Political Subdivisions [Member] | Baa/BBB Ratings [Member] |  |
Debt Securities Held To Maturity Credit Quality Indicator [Line Items] |  |
Amortized cost | 2,980 | 2,980
Corporate Bonds [Member] |  |
Debt Securities Held To Maturity Credit Quality Indicator [Line Items] |  |
Balance | 241 | 143
Provision for credit loss expense (benefit) | (13) | 85
Balance | 228 | 228
Amortized cost | 66,419 | 66,419
Corporate Bonds [Member] | AAA/AA/A Ratings [Member] |  |
Debt Securities Held To Maturity Credit Quality Indicator [Line Items] |  |
Amortized cost | 26,995 | 26,995
Corporate Bonds [Member] | Baa/BBB Ratings [Member] |  |
Debt Securities Held To Maturity Credit Quality Indicator [Line Items] |  |
Amortized cost | 39,424 | 39,424
U.S. Agency-Based Mortgage-Backed Securities [Member] |  |
Debt Securities Held To Maturity Credit Quality Indicator [Line Items] |  |
Amortized cost | 4,102 | 4,102
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 | 4,102 | 4,102
U.S. Treasury Securities and Obligations of U.S. Government Agencies [Member] |  |
Debt Securities Held To Maturity Credit Quality Indicator [Line Items] |  |
Amortized cost | 17,182 | 17,182
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 | 17,182 | 17,182
Asset-Backed Securities [Member] |  |
Debt Securities Held To Maturity Credit Quality Indicator [Line Items] |  |
Balance | 4 | 4
Balance | 4 | 4
Amortized cost | 89 | 89
Asset-Backed Securities [Member] | AAA/AA/A Ratings [Member] |  |
Debt Securities Held To Maturity Credit Quality Indicator [Line Items] |  |
Amortized cost | 62 | 62
Asset-Backed Securities [Member] | Baa/BBB Ratings [Member] |  |
Debt Securities Held To Maturity Credit Quality Indicator [Line Items] |  |
Amortized cost | 12 | 12
Asset-Backed Securities [Member] | B Ratings [Member] |  |
Debt Securities Held To Maturity Credit Quality Indicator [Line Items] |  |
Amortized cost | $ 15 | $ 15

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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 -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 50 -Paragraph 13 -Subparagraph (a) -URI https://asc.fasb.org/extlink&oid=124255953&loc=SL82919249-210447 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 5 -Subparagraph (aaa) -URI https://asc.fasb.org/extlink&oid=126970911&loc=d3e27232-111563 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 45 -Paragraph 1 -URI https://asc.fasb.org/extlink&oid=124255206&loc=SL82895884-210446 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 50 -Paragraph 13 -Subparagraph (f) -URI https://asc.fasb.org/extlink&oid=124255953&loc=SL82919249-210447 + Details
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- Definition Amount of expense (reversal of expense) for expected credit loss on investment in debt security measured at amortized cost (held-to-maturity). + 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 https://asc.fasb.org/extlink&oid=124255953&loc=SL82919249-210447 + Details
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