Summary of Significant Accounting Policies - Real Estate Loans Receivable (Details)	Sep. 30, 2018 mezzanine_loan
Mezzanine Loan Receivable
Property, Plant and Equipment [Line Items]
Number of mezzanine loans collateralized	7
Term Loan Receivable
Property, Plant and Equipment [Line Items]
Number of mezzanine loans collateralized	1

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration