Financial Instruments and Fair Value Measurements - Additional Information (Details) - USD ($)	3 Months Ended		12 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Gain on disposition of properties			$ 30,324,000	$ 5,140,000	$ 48,886,000
Impairment charge	$ 300,000	$ 1,400,000	1,721,000		14,455,000
Reclassification adjustment related to derivatives from AOCI to interest expense			5,200,000
Derivatives designated as fair value hedges			0	0
Derivative designated to hedges of net investments in foreign operations			$ 0	0
Nonrecurring | Disposal group, held-for-sale
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Impairment charge				0
Nonrecurring | Disposal group, held-for-sale | Fund IV | 210 Bowery property
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Gain on disposition of properties				0
Impairment charge	300,000	1,400,000		$ 0
Nonrecurring | Disposal group, held-for-sale | Property Classified As Held For Sale At September 30, 2017
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Impairment charge					3,800,000
Nonrecurring | Disposal group, held-for-sale | Property Classified As Held For Sale At December 31, 2017
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Impairment charge					10,600,000
Nonrecurring | Disposal group, held-for-sale | Noncontrolling Interests | Fund IV | 210 Bowery property
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Impairment charge	$ 200,000	$ 1,100,000
Nonrecurring | Disposal group, held-for-sale | Noncontrolling Interests | Property Classified As Held For Sale At September 30, 2017
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Impairment charge					2,700,000
Nonrecurring | Disposal group, held-for-sale | Noncontrolling Interests | Property Classified As Held For Sale At December 31, 2017
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Impairment charge					$ 7,600,000