Summary of Significant Accounting Policies - Real Estate Loans Receivable (Details)	Jun. 30, 2018 mezzanine_loan
Mezzanine Loan Receivable
Property, Plant and Equipment [Line Items]
Number of mezzanine loans collateralized	8
Term Loan Receivable
Property, Plant and Equipment [Line Items]
Number of mezzanine loans collateralized	2

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.

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