Investments in Unconsolidated Joint Ventures - Summary of Investments and Income from Investments In Unconsolidated Joint Ventures (Parenthetical) (Details)	3 Months Ended
	Mar. 31, 2019 USD ($)
712 Fifth Avenue [Member]
Schedule Of Equity Method Investments [Line Items]
Distributions made in excess of share of earnings recognized negative basis	$ 16,340
60 Wall Street [Member]
Schedule Of Equity Method Investments [Line Items]
Difference between carrying amount of investment and equity	2,760,000
One Steuart Lane [Member]
Schedule Of Equity Method Investments [Line Items]
Difference between carrying amount of investment and equity	935,000
Oder-Center, Germany [Member]
Schedule Of Equity Method Investments [Line Items]
Difference between carrying amount of investment and equity	$ 5,027,000