Real Estate Fund Investments - Summary of Ownership Interest in Fund VIII and Underlying Investments in Fund VIII (Parenthetical) (Details)	3 Months Ended
	Mar. 31, 2016 USD ($) ft²
Investment Holdings [Line Items]
Area of office properties	10,400,000
Mezzanine Secured Loan | 26 Broadway [Member]
Investment Holdings [Line Items]
Area of office properties	836,000
Subordinate loan | $	$ 220,000
Subordinate to other debt	The loan has a fixed interest rate and is subordinate to $220,000 of other debt.
Mezzanine Secured Loan | 1440 Broadway [Member]
Investment Holdings [Line Items]
Area of office properties	751,546
Subordinate loan | $	$ 265,000
Subordinate to other debt	The loan bears interest at LIBOR plus 600 bps, has a one-year extension option and is subordinate to $265,000 of other debt
Loan extension term	1 year
Mezzanine Secured Loan | 1440 Broadway [Member] | London Interbank Offered Rate L I B O R
Investment Holdings [Line Items]
Basis spread on variable rate	6.00%
Mezzanine Secured Loan | 700 Eighth Avenue [Member]
Investment Holdings [Line Items]
Area of office properties	26,126
Loan extension term	1 year
Mezzanine Secured Loan | 700 Eighth Avenue [Member] | London Interbank Offered Rate L I B O R
Investment Holdings [Line Items]
Basis spread on variable rate	6.00%