Fair Value Measurement - Narrative (Details) - USD ($)	12 Months Ended
Dec. 31, 2024	Dec. 31, 2023
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Percentage of portfolio of unadjusted fair values obtained	98.40%
Three private equity funds using NAV	$ 90,700,000
Transfers between Levels 1, 2, and 3 of the fair value hierarchy	0	$ 0
Fair Value, Nonrecurring
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets, fair value disclosure	0	0
Liabilities, fair value disclosure	0	0
Unsecured Notes Two \| Revolving Credit Facility
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Drawn down amount under credit facility	$ 200,000,000	200,000,000
Minimum
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value, liquidating investment, remaining period	1 year
Maximum
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value, liquidating investment, remaining period	8 years
Venture Capital Investments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
One private equity fund using NAV	$ 4,500,000
Private Equity Funds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Unfunded commitments	5,000,000	8,000,000
Level 2 \| Unsecured notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Unsecured notes	375,000,000	375,000,000
Level 2 \| Commercial Mortgage Back Securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt securities, trading, and equity securities, FV-NI	$ 16,000,000.0	$ 33,000,000.0

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One Private Equity Fund using NAV

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Percentage of unadjusted fair value obtained

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Three Private Equity Funds Using NAV

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Fair value portion of asset recognized for present right to economic benefit.

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Face (par) amount of debt instrument at time of issuance.

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Remaining period of expected liquidation by investee of underlying asset of investment measured at net asset value per share or unit. In 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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The amount of unfunded commitments for which the entity is obligated, to those certain investments for which net asset value per share is calculated (including by unit, membership interest, or other equity (ownership interest) unit measure) (alternative investments).

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Fair value of financial and nonfinancial obligations.

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Amount of cash inflow from contractual arrangement with the lender, including but not limited to, letter of credit, standby letter of credit and revolving credit arrangements.

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Amount of investment in debt security measured at fair value with change in fair value recognized in net income (trading) and investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

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