Impairment Charges and Reserves - Summary of Significant Unobservable Inputs (Detail) - Fair Value Measurements [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Consolidated Assets, Fair Value	$ 11.5	$ 5.0	$ 51.5
Preferred equity interests, Fair Value	94.2	108.5	185.5
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Consolidated Assets, Fair Value	11.5	5.0	51.5
Preferred equity interests, Fair Value	94.2	108.5	$ 185.5
Impairment of Consolidated Assets [Member] | Level 3 [Member] | Indicative Bid [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Consolidated Assets, Fair Value	11.5	5.0
Preferred Equity Interests [Member] | Level 3 [Member] | Discounted Cash Flow [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Preferred equity interests, Fair Value	$ 94.2	$ 108.5
Preferred Equity Interests [Member] | Level 3 [Member] | Discounted Cash Flow [Member] | Discount Rate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Unobservable inputs rate	7.90%
Preferred Equity Interests [Member] | Level 3 [Member] | Discounted Cash Flow [Member] | Terminal Capitalization Rate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Unobservable inputs rate	8.20%
Preferred Equity Interests [Member] | Level 3 [Member] | Discounted Cash Flow [Member] | NOI Growth Rate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Unobservable inputs rate		1.00%
Unobservable inputs rate	0.00%
Preferred Equity Interests [Member] | Level 3 [Member] | Discounted Cash Flow [Member] | Minimum [Member] | Discount Rate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Unobservable inputs rate	6.60%	8.90%
Preferred Equity Interests [Member] | Level 3 [Member] | Discounted Cash Flow [Member] | Minimum [Member] | Terminal Capitalization Rate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Unobservable inputs rate	6.60%	8.30%
Preferred Equity Interests [Member] | Level 3 [Member] | Discounted Cash Flow [Member] | Maximum [Member] | Discount Rate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Unobservable inputs rate	10.60%	9.90%
Preferred Equity Interests [Member] | Level 3 [Member] | Discounted Cash Flow [Member] | Maximum [Member] | Terminal Capitalization Rate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Unobservable inputs rate	10.50%	9.40%
Preferred Equity Interests [Member] | Level 3 [Member] | Discounted Cash Flow [Member] | Maximum [Member] | NOI Growth Rate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Unobservable inputs rate	0.00%