Notes Receivable, Net - Schedule of Notes Receivable (Details) $ in Thousands	Sep. 30, 2017 USD ($) debtinstrument	Dec. 31, 2016 USD ($)
Mortgage Loans on Real Estate [Line Items]
Net carrying amount of notes receivable | $	$ 250,194	$ 276,163
Number of instruments held | debtinstrument	7
Fund II
Mortgage Loans on Real Estate [Line Items]
Net carrying amount of notes receivable | $	$ 31,593	31,007
Number of instruments held | debtinstrument	1
Effective interest rate	2.50%
Fund III
Mortgage Loans on Real Estate [Line Items]
Net carrying amount of notes receivable | $	$ 4,956	4,506
Number of instruments held | debtinstrument	1
Effective interest rate	18.00%
Fund IV
Mortgage Loans on Real Estate [Line Items]
Net carrying amount of notes receivable | $	$ 15,250	24,250
Number of instruments held | debtinstrument	1
Effective interest rate	15.30%
Core Portfolio
Mortgage Loans on Real Estate [Line Items]
Net carrying amount of notes receivable | $	$ 198,395	$ 216,400
Number of instruments held | debtinstrument	4
Core Portfolio | Minimum
Mortgage Loans on Real Estate [Line Items]
Effective interest rate	6.00%
Core Portfolio | Maximum
Mortgage Loans on Real Estate [Line Items]
Effective interest rate	8.70%