Impairment Charges and Reserves - Summary of Significant Unobservable Inputs (Detail) - Fair Value Measurements [Member] $ in Millions	3 Months Ended
	Mar. 31, 2019 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Consolidated Assets, Fair Value	$ 0.8
Preferred Equity Interests, Fair Value	172.0
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Consolidated Assets, Fair Value	0.8
Preferred Equity Interests, Fair Value	172.0
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	0.8
Reserve of 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	$ 172.0
Reserve of 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%
Reserve of 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	8.70%
Reserve of 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	8.20%
Reserve of 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	8.80%
Reserve of 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	8.60%