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Income from Investments - Net Investment Income (Details) - USD ($) | 12 Months Ended
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Dec. 31, 2024 | Dec. 31, 2023 | Dec. 31, 2022
Net Investment Income [Line Items] |  |  |
Investment income | $ 434,200,000 | $ 447,100,000 | $ 450,600,000
Investment expenses | 26,700,000 | 27,400,000 | 28,000,000.0
Net investment income | 407,500,000 | 419,700,000 | 422,600,000
Interest on Fixed Income Securities |  |  |
Net Investment Income [Line Items] |  |  |
Investment income | 315,300,000 | 323,300,000 | 290,000,000.0
Dividends on Equity Securities Excluding Alternative Investments |  |  |
Net Investment Income [Line Items] |  |  |
Investment income | 5,400,000 | 4,400,000 | 6,300,000
Total Alternative Investments |  |  |
Net Investment Income [Line Items] |  |  |
Investment income | 6,300,000 | 29,500,000 | 73,400,000
Equity Method Limited Liability Investments |  |  |
Net Investment Income [Line Items] |  |  |
Investment income |  | 10,500,000 | 31,300,000
Investment expenses | 18,200,000 |  |
Limited Liability Investments Included in Equity Securities |  |  |
Net Investment Income [Line Items] |  |  |
Investment income | 24,500,000 | 19,000,000.0 | 42,100,000
Short-term Investments |  |  |
Net Investment Income [Line Items] |  |  |
Investment income | 33,500,000 | 18,000,000.0 | 3,700,000
Loans to Policyholders |  |  |
Net Investment Income [Line Items] |  |  |
Investment income | 21,000,000.0 | 20,900,000 | 21,500,000
Real Estate |  |  |
Net Investment Income [Line Items] |  |  |
Investment income | 8,800,000 | 8,900,000 | 10,100,000
Investment expenses | 8,700,000 | 8,800,000 | 7,900,000
Other |  |  |
Net Investment Income [Line Items] |  |  |
Investment income | 8,200,000 | 12,900,000 | 7,700,000
Investment expenses | 18,000,000.0 | 18,600,000 | 20,100,000
Cash Surrender Value |  |  |
Net Investment Income [Line Items] |  |  |
Investment income | 35,700,000 | 29,200,000 | 37,900,000
Universal Life-type Policyholder Account Balances |  |  |
Net Investment Income [Line Items] |  |  |
Interest Expense, Other Short-Term Borrowings | $ 20,300,000 | $ 22,700,000 | $ 10,100,000

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- Definition Amount, before investment expense, of income earned from investments in securities and real estate. Includes, but is not limited to, real estate investment, policy loans, dividends, and interest. Excludes realized gain (loss) on investments. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Topic 946 -SubTopic 830 -Name Accounting Standards Codification -Section 55 -Paragraph 10 -Publisher FASB -URI https://asc.fasb.org/1943274/2147479168/946-830-55-10 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 944 -SubTopic 220 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-04(2)(b)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147477250/944-220-S99-1 Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 946 -SubTopic 220 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.6-07(1)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147479134/946-220-S99-1 + Details
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