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Significant Accounting Policies - Additional Information (Detail) $ in Millions | 12 Months Ended
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Dec. 31, 2025 USD ($) Integer | Dec. 31, 2024 USD ($) | Dec. 31, 2023 USD ($)
Accounting Policies [Abstract] |  |  |
Number of Operating Segments | Integer | 3 |  |
Premiums Receivable, Gross | $ 579.5 | $ 584.1 |
Ceded Policy Loans | 3,353.8 | 3,313.6 |
Premium Receivable, Allowance for Credit Loss | 26.1 | 26.8 |
Premium Receivable, Credit Loss Expense (Reversal) | (0.7) | (2.7) |
Accumulated Depreciation for Property and Equipment | 1,629.7 | 1,501.3 |
Value of Business Acquired | 56.9 | 55.1 |
Accumulated Amortization of Value of Business Acquired | 181.9 | 165.5 |
Amortization of Value of Business Acquired | 6.0 | 6.2 | $ 5.2
Prepaid Reinsurance Premiums | 1,239.5 | 508.0 |
Deferred Gain on Reinsurance | 138.0 | 4.9 |
Reinsurance Recoverable, Allowance for Credit Loss | 1.4 | 1.5 |
Premium Tax Expense | 189.0 | 194.5 | $ 183.5
Participation Fund Account Assets (PFA) | $ 232.0 | $ 231.3 |

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- Definition Loans ceded to reinsurers. These loans use insurance policy funds such as cash surrender values as collateral. + References No definition available. + Details
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- Definition Accumulated amortization of other deferred costs capitalized at the end of the reporting period. Does not include deferred finance costs, deferred acquisition costs of insurance companies, or deferred leasing costs for real estate operations. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 210 -SubTopic 10 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(17)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480566/210-10-S99-1 + Details
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- Definition Amount of accumulated depreciation, depletion and amortization for physical assets used in the normal conduct of business to produce goods and services. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 944 -SubTopic 210 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03(a)(8)(b)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147478777/944-210-S99-1 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 210 -SubTopic 10 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(14)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480566/210-10-S99-1 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Topic 360 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (c) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482099/360-10-50-1 + Details
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- Definition Number of operating segments. An operating segment is a component of an enterprise: (a) that engages in business activities from which it may earn revenues and incur expenses (including revenues and expenses relating to transactions with other components of the same enterprise), (b) whose operating results are regularly reviewed by the enterprise's chief operating decision maker to make decisions about resources to be allocated to the segment and assess its performance, and (c) for which discrete financial information is available. An operating segment may engage in business activities for which it has yet to earn revenues, for example, start-up operations may be operating segments before earning revenues. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Topic 280 -SubTopic 10 -Name Accounting Standards Codification -Section 55 -Paragraph 49 -Publisher FASB -URI https://asc.fasb.org/1943274/2147482785/280-10-55-49 Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 280 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 18 -Publisher FASB -URI https://asc.fasb.org/1943274/2147482810/280-10-50-18 + Details
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- Definition Amount of expense (reversal of expense) for expected credit loss on premium receivable. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -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/2009/role/commonPracticeRef -Name Accounting Standards Codification -Section 50 -Paragraph 22 -Subparagraph (a) -SubTopic 40 -Topic 220 -Publisher FASB -URI https://asc.fasb.org/1943274/2147476148/220-40-50-22 + Details
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- Definition Gross amount, as of the balance sheet date, due the entity from (a) agents and insureds, (b) uncollected premiums and (c) others, before deducting the allowance for doubtful accounts. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 944 -SubTopic 210 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03(a)(5)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147478777/944-210-S99-1 + Details
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