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Investments in and Advances to Unconsolidated Affiliates - Mervyns I & II - Additional Information (Details) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended | 12 Months Ended
--- | --- | --- | ---
Dec. 31, 2020 | Jun. 30, 2020 | Sep. 30, 2021 | Dec. 31, 2020
Mervyns II |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |
Realized gain on investment | $ 0.4 | $ 22.8 |  |
Cost method investments effective ownership, shares |  |  | 4.1 |
Cost method investments effective ownership interest |  |  | 1.00% |
Unrealized gain on investment |  | $ 64.9 | $ 55.8 |
Albertson |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |
Unrealized gain on investment |  |  |  | $ 7.5

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