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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, 2025 USD ($)	Sep. 30, 2025 USD ($)
Debt Securities Held To Maturity Credit Quality Indicator [Line Items]
Balance	$ 88	$ 116
Provision for credit loss benefit	(8)	(36)
Balance	80	80
Amortized cost	372,098	372,098
AAA/AA/A Ratings [Member]
Debt Securities Held To Maturity Credit Quality Indicator [Line Items]
Amortized cost	360,242	360,242
Baa/BBB Ratings [Member]
Debt Securities Held To Maturity Credit Quality Indicator [Line Items]
Amortized cost	11,856	11,856
States and Political Subdivisions [Member]
Debt Securities Held To Maturity Credit Quality Indicator [Line Items]
Balance	27	30
Provision for credit loss benefit	(3)	(6)
Balance	24	24
Amortized cost	339,321	339,321
States and Political Subdivisions [Member] | AAA/AA/A Ratings [Member]
Debt Securities Held To Maturity Credit Quality Indicator [Line Items]
Amortized cost	339,321	339,321
States and Political Subdivisions [Member] | Baa/BBB Ratings [Member]
Debt Securities Held To Maturity Credit Quality Indicator [Line Items]
Amortized cost	0	0
Corporate Bonds [Member]
Debt Securities Held To Maturity Credit Quality Indicator [Line Items]
Balance	61	86
Provision for credit loss benefit	(5)	(30)
Balance	56	56
Amortized cost	21,733	21,733
Corporate Bonds [Member] | AAA/AA/A Ratings [Member]
Debt Securities Held To Maturity Credit Quality Indicator [Line Items]
Amortized cost	9,886	9,886
Corporate Bonds [Member] | Baa/BBB Ratings [Member]
Debt Securities Held To Maturity Credit Quality Indicator [Line Items]
Amortized cost	11,847	11,847
U.S. Agency-Based Mortgage-Backed Securities [Member]
Debt Securities Held To Maturity Credit Quality Indicator [Line Items]
Amortized cost	2,490	2,490
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	2,490	2,490
U.S. Treasury Securities and Obligations of U.S. Government Agencies [Member]
Debt Securities Held To Maturity Credit Quality Indicator [Line Items]
Amortized cost	8,545	8,545
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	8,545	8,545
Asset-Backed Securities [Member]
Debt Securities Held To Maturity Credit Quality Indicator [Line Items]
Balance	0	0
Provision for credit loss benefit	(0)	(0)
Balance	0	0
Amortized cost	9	9
Asset-Backed Securities [Member] | AAA/AA/A Ratings [Member]
Debt Securities Held To Maturity Credit Quality Indicator [Line Items]
Amortized cost	0	0
Asset-Backed Securities [Member] | Baa/BBB Ratings [Member]
Debt Securities Held To Maturity Credit Quality Indicator [Line Items]
Amortized cost	$ 9	$ 9

X

- 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 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

Reference 2: 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 3: 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 4: 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

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X

- 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
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-13

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 220
-SubTopic 40
-Name Accounting Standards Codification
-Section 50
-Paragraph 22
-Subparagraph (a)
-Publisher FASB
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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 5
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-5

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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
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-6

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