Investments in Unconsolidated Joint Ventures - Summary of Investments and Income from Investments In Unconsolidated Joint Ventures (Parenthetical) (Details) - USD ($)		6 Months Ended
	May 05, 2017	Jun. 30, 2017	Jun. 13, 2017	May 04, 2017
Schedule Of Equity Method Investments [Line Items]
Distributions of capital from unconsolidated joint ventures		$ 20,000,000
712 Fifth Avenue [Member]
Schedule Of Equity Method Investments [Line Items]
Mortgage refinancing extended amount			$ 300,000,000
Basis of investment property		4,928,000
Distributions of capital from unconsolidated joint ventures		$ 20,000,000
Property ownership, percentage		50.00%
712 Fifth Avenue [Member] | Income From Unconsolidated Joint Ventures [Member]
Schedule Of Equity Method Investments [Line Items]
Distributions of capital from unconsolidated joint ventures		$ 15,072,000
RDF [Member] | 75 Howard [Member]
Schedule Of Equity Method Investments [Line Items]
Property ownership, percentage				100.00%
Ownership percentage in residential fund	7.40%	7.40%
Economic interest percentage	1.50%	1.50%