Summary of Significant Accounting Policies - Real Estate Loans Receivable (Details)	Mar. 31, 2019 mezzanine_loan
Mezzanine Loan Receivable
Property, Plant and Equipment [Line Items]
Number of mezzanine loans collateralized	10
Term Loan Receivable
Property, Plant and Equipment [Line Items]
Number of mezzanine loans collateralized	2
Construction Loans
Property, Plant and Equipment [Line Items]
Number of mezzanine loans collateralized	1