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, 2026 USD ($)	Jun. 30, 2026 USD ($)
Debt Securities Held To Maturity Credit Quality Indicator [Line Items]
Balance	$ 65	$ 73
Provision for credit loss benefit	(5)	(13)
Balance	60	60
Amortized cost	332,774	332,774
AAA/AA/A Ratings [Member]
Debt Securities Held To Maturity Credit Quality Indicator [Line Items]
Amortized cost	326,295	326,295
Baa/BBB Ratings [Member]
Debt Securities Held To Maturity Credit Quality Indicator [Line Items]
Amortized cost	6,479	6,479
States and Political Subdivisions [Member]
Debt Securities Held To Maturity Credit Quality Indicator [Line Items]
Balance	22	23
Provision for credit loss benefit	(1)	(2)
Balance	21	21
Amortized cost	305,868	305,868
States and Political Subdivisions [Member] \| AAA/AA/A Ratings [Member]
Debt Securities Held To Maturity Credit Quality Indicator [Line Items]
Amortized cost	305,868	305,868
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	43	50
Provision for credit loss benefit	(4)	(11)
Balance	39	39
Amortized cost	16,050	16,050
Corporate Bonds [Member] \| AAA/AA/A Ratings [Member]
Debt Securities Held To Maturity Credit Quality Indicator [Line Items]
Amortized cost	9,580	9,580
Corporate Bonds [Member] \| Baa/BBB Ratings [Member]
Debt Securities Held To Maturity Credit Quality Indicator [Line Items]
Amortized cost	6,470	6,470
U.S. Agency-Based Mortgage-Backed Securities [Member]
Debt Securities Held To Maturity Credit Quality Indicator [Line Items]
Amortized cost	2,234	2,234
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	2,234	2,234
U.S. Treasury Securities and Obligations of U.S. Government Agencies [Member]
Debt Securities Held To Maturity Credit Quality Indicator [Line Items]
Amortized cost	8,613	8,613
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	8,613	8,613
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

Amount of allowance for credit loss for debt security measured at amortized cost (held-to-maturity).

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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- 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
-URI https://asc.fasb.org/1943274/2147476148/220-40-50-22

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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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