Real Estate Fund Investments - Summary of Investments of Alternative Investment Funds (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2015	Dec. 31, 2014
Investment Holdings [Line Items]
Mezzanine Loans, Interest Rate	5.50%
Investment , total	$ 141,131	$ 140,171
Property Fund VIII
Investment Holdings [Line Items]
Mezzanine Loans, Ownership	1.70%
Mezzanine Loans, Initial Maturity	Oct. 31, 2019
Mezzanine Loans, Initial Maturity	Jan. 31, 2022
Mezzanine loans	$ 86,813	45,947
Property Fund VIII | Minimum
Investment Holdings [Line Items]
Mezzanine Loans, Interest Rate	6.00%
Property Fund VIII | Maximum
Investment Holdings [Line Items]
Mezzanine Loans, Interest Rate	8.30%
PGRESS Funds
Investment Holdings [Line Items]
Preferred Equity Investments, Ownership	4.90%
Preferred Equity Investments, Dividend Rate	10.30%
Preferred Equity Investments, Initial Maturity	2017-04
Preferred Equity Investments, Initial Maturity	2019-02
Preferred Equity Investments, Investment	$ 54,318	$ 94,224