Investments in and Advances to Unconsolidated Affiliates - Mervyns I & II - Additional Information (Details) - USD ($) shares in Millions, $ in Millions	3 Months Ended			12 Months Ended
	Mar. 31, 2021	Dec. 31, 2020	Jun. 30, 2020	Dec. 31, 2020
Mervyns II
Schedule of Equity Method Investments [Line Items]
Cost method investment, ownership percentage	28.33%
Realized gain on investment	$ 0.4	$ 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
Albertson
Schedule of Equity Method Investments [Line Items]
Cost method investment, ownership percentage	36.67%
Albertson | Mervyns II
Schedule of Equity Method Investments [Line Items]
Unrealized gain on investment	$ 6.1			$ 7.5