Subsequent Events - Additional Information (Details)	Oct. 29, 2015 USD ($) ft²	Oct. 01, 2015 USD ($)	Sep. 30, 2015 ft²
Subsequent Event [Line Items]
Area of office properties | ft²			10,400,000
Subsequent Events [Member] | Fund VII and VII-H [Member] | 670 Broadway [Member]
Subsequent Event [Line Items]
Business acquisition, consideration amount	$ 112,000,000
Business acquisition, consideration cash	$ 42,000,000
Area of office properties | ft²	77,480
Subsequent Events [Member] | Mortgage Debt [Member] | Fund VII and VII-H [Member] | 670 Broadway [Member]
Subsequent Event [Line Items]
Business acquisition, consideration debt	$ 70,000,000
Subsequent Events [Member] | 31 West 52nd Street [Member]
Subsequent Event [Line Items]
Business acquisition of remaining ownership interest percentage		35.80%
Business acquisition, consideration amount		$ 378,000,000
Business acquisition, consideration cash		230,000,000
Business acquisition, consideration debt		$ 148,000,000