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Fair Value Measurement (Narrative) (Details) - USD ($) | 6 Months Ended | 12 Months Ended
--- | --- | ---
Jun. 30, 2023 | Jun. 30, 2022 | Dec. 31, 2022
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |
Percentage of portfolio of unadjusted fair values obtained | 98.20% |  |
Three private equity funds using NAV | $ 85,400,000 |  |
Fair Value, Assets, Level 1 to Level 2 to Level 3 Transfers, Amount | 0 | $ 0 |
Unsecured Notes Two | Revolving Credit Facility |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |
Drawn down amount under credit facility | $ 75,000,000 |  | $ 25,000,000
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 | 9 years |  |
Technology, Healthcare, Specialty Customer Goods and Service |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |
One private equity fund using NAV | $ 0 |  |
Venture Capital Investments |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |
One private equity fund using NAV | 1,600,000 |  |
Private Equity Funds |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |
Unfunded commitments to VIEs | 8,000,000 |  | 9,000,000
Level 2 | Unsecured debt |  |  |
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 | $ 25,500,000 |  | $ 27,300,000

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