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Investments (Aggregated Income Statement Summarized Financial Information for Partnerhips in our Alternative Investment Portfolio) (Details) - USD ($) $ in Thousands | 3 Months Ended
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Mar. 31, 2023 | Mar. 31, 2022
Schedule of Equity Method Investments [Line Items] |  |
Net investment income earned | $ 91,506 | $ 72,602
Investments accounted for under the equity method [Member] |  |
Schedule of Equity Method Investments [Line Items] |  |
Net investment income | (70,700) | 135,500
Realized gains | 1,722,300 | 2,748,000
Net change in unrealized appreciation | 1,443,700 | 5,178,200
Net income | 3,095,300 | 8,061,700
Alternative Investments [Member] |  |
Schedule of Equity Method Investments [Line Items] |  |
Net investment income earned | $ 7,768 | $ 19,128

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