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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 | 12 Months Ended
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Dec. 31, 2020 USD ($)
Debt Securities Held To Maturity Credit Quality Indicator [Line Items] |
Balance | $ 301
Provision for credit loss benefit | (27)
Balance | 274
Amortized cost | 585,404
AAA/AA/A Ratings [Member] |
Debt Securities Held To Maturity Credit Quality Indicator [Line Items] |
Amortized cost | 541,199
Baa/BBB Ratings [Member] |
Debt Securities Held To Maturity Credit Quality Indicator [Line Items] |
Amortized cost | 44,172
B Ratings [Member] |
Debt Securities Held To Maturity Credit Quality Indicator [Line Items] |
Amortized cost | 33
States and Political Subdivisions [Member] |
Debt Securities Held To Maturity Credit Quality Indicator [Line Items] |
Balance | 45
Provision for credit loss benefit | (3)
Balance | 42
Amortized cost | 494,374
States and Political Subdivisions [Member] | AAA/AA/A Ratings [Member] |
Debt Securities Held To Maturity Credit Quality Indicator [Line Items] |
Amortized cost | 490,311
States and Political Subdivisions [Member] | Baa/BBB Ratings [Member] |
Debt Securities Held To Maturity Credit Quality Indicator [Line Items] |
Amortized cost | 4,063
Corporate Bonds [Member] |
Debt Securities Held To Maturity Credit Quality Indicator [Line Items] |
Balance | 245
Provision for credit loss benefit | (20)
Balance | 225
Amortized cost | 69,981
Corporate Bonds [Member] | AAA/AA/A Ratings [Member] |
Debt Securities Held To Maturity Credit Quality Indicator [Line Items] |
Amortized cost | 29,890
Corporate Bonds [Member] | Baa/BBB Ratings [Member] |
Debt Securities Held To Maturity Credit Quality Indicator [Line Items] |
Amortized cost | 40,091
U.S. Agency-Based Mortgage-Backed Securities [Member] |
Debt Securities Held To Maturity Credit Quality Indicator [Line Items] |
Amortized cost | 7,261
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 | 7,261
U.S. Treasury Securities and Obligations of U.S. Government Agencies [Member] |
Debt Securities Held To Maturity Credit Quality Indicator [Line Items] |
Amortized cost | 13,626
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 | 13,626
Asset-Backed Securities [Member] |
Debt Securities Held To Maturity Credit Quality Indicator [Line Items] |
Balance | 11
Provision for credit loss benefit | (4)
Balance | 7
Amortized cost | 162
Asset-Backed Securities [Member] | AAA/AA/A Ratings [Member] |
Debt Securities Held To Maturity Credit Quality Indicator [Line Items] |
Amortized cost | 111
Asset-Backed Securities [Member] | Baa/BBB Ratings [Member] |
Debt Securities Held To Maturity Credit Quality Indicator [Line Items] |
Amortized cost | 18
Asset-Backed Securities [Member] | B Ratings [Member] |
Debt Securities Held To Maturity Credit Quality Indicator [Line Items] |
Amortized cost | $ 33

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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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