Notes Receivable, Net - Schedule of Notes Receivable (Details) $ in Thousands	Mar. 31, 2018 USD ($) debtinstrument	Dec. 31, 2017 USD ($)
Mortgage Loans on Real Estate [Line Items]
Net carrying amount of notes receivable | $	$ 108,959	$ 153,829
Number of instruments held | debtinstrument	5
Core Portfolio
Mortgage Loans on Real Estate [Line Items]
Net carrying amount of notes receivable | $	$ 56,475	101,695
Number of instruments held | debtinstrument	2
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	8.10%
Fund Portfolio | Fund II
Mortgage Loans on Real Estate [Line Items]
Net carrying amount of notes receivable | $	$ 31,978	31,778
Number of instruments held | debtinstrument	1
Effective interest rate	2.50%
Fund Portfolio | Fund III
Mortgage Loans on Real Estate [Line Items]
Net carrying amount of notes receivable | $	$ 5,256	5,106
Number of instruments held | debtinstrument	1
Effective interest rate	18.00%
Fund Portfolio | Fund IV
Mortgage Loans on Real Estate [Line Items]
Net carrying amount of notes receivable | $	$ 15,250	$ 15,250
Number of instruments held | debtinstrument	1
Effective interest rate	15.30%