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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
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Mar. 31, 2021 USD ($)
Debt Securities Held To Maturity Credit Quality Indicator [Line Items] |
Balance | $ 274
Provision for credit loss expense (benefit) | (108)
Balance | 166
Amortized cost | 575,274
AAA/AA/A Ratings [Member] |
Debt Securities Held To Maturity Credit Quality Indicator [Line Items] |
Amortized cost | 531,704
Baa/BBB Ratings [Member] |
Debt Securities Held To Maturity Credit Quality Indicator [Line Items] |
Amortized cost | 43,541
B Ratings [Member] |
Debt Securities Held To Maturity Credit Quality Indicator [Line Items] |
Amortized cost | 29
States and Political Subdivisions [Member] |
Debt Securities Held To Maturity Credit Quality Indicator [Line Items] |
Balance | 42
Provision for credit loss expense (benefit) | 2
Balance | 44
Amortized cost | 486,376
States and Political Subdivisions [Member] | AAA/AA/A Ratings [Member] |
Debt Securities Held To Maturity Credit Quality Indicator [Line Items] |
Amortized cost | 481,662
States and Political Subdivisions [Member] | Baa/BBB Ratings [Member] |
Debt Securities Held To Maturity Credit Quality Indicator [Line Items] |
Amortized cost | 4,714
Corporate Bonds [Member] |
Debt Securities Held To Maturity Credit Quality Indicator [Line Items] |
Balance | 225
Provision for credit loss expense (benefit) | (109)
Balance | 116
Amortized cost | 68,518
Corporate Bonds [Member] | AAA/AA/A Ratings [Member] |
Debt Securities Held To Maturity Credit Quality Indicator [Line Items] |
Amortized cost | 29,708
Corporate Bonds [Member] | Baa/BBB Ratings [Member] |
Debt Securities Held To Maturity Credit Quality Indicator [Line Items] |
Amortized cost | 38,810
U.S. Agency-Based Mortgage-Backed Securities [Member] |
Debt Securities Held To Maturity Credit Quality Indicator [Line Items] |
Amortized cost | 6,357
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 | 6,357
U.S. Treasury Securities and Obligations of U.S. Government Agencies [Member] |
Debt Securities Held To Maturity Credit Quality Indicator [Line Items] |
Amortized cost | 13,877
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 | 13,877
Asset-Backed Securities [Member] |
Debt Securities Held To Maturity Credit Quality Indicator [Line Items] |
Balance | 7
Provision for credit loss expense (benefit) | (1)
Balance | 6
Amortized cost | 146
Asset-Backed Securities [Member] | AAA/AA/A Ratings [Member] |
Debt Securities Held To Maturity Credit Quality Indicator [Line Items] |
Amortized cost | 100
Asset-Backed Securities [Member] | Baa/BBB Ratings [Member] |
Debt Securities Held To Maturity Credit Quality Indicator [Line Items] |
Amortized cost | 17
Asset-Backed Securities [Member] | B Ratings [Member] |
Debt Securities Held To Maturity Credit Quality Indicator [Line Items] |
Amortized cost | $ 29

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- Definition Securities held to maturity allowance for credit loss. + References No definition available. + 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 http://asc.fasb.org/extlink&oid=121599337&loc=SL82919249-210447 + Details
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- Definition Amount of investment in debt security measured at amortized cost (held-to-maturity) originated in current fiscal year. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 50 -Paragraph 6 -URI http://asc.fasb.org/extlink&oid=121599337&loc=SL82919232-210447 + Details
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