Summary of Significant Accounting Policies - Real Estate Loans Receivable (Details)	9 Months Ended
	Sep. 30, 2017 buildings mezzanine_loan
Property, Plant and Equipment [Line Items]
Number of medical office building developments as collateral for real estate loans receivable | buildings	2
Mezzanine Loan Receivable
Property, Plant and Equipment [Line Items]
Number of mezzanine loans collateralized	11
Term Loan Receivable
Property, Plant and Equipment [Line Items]
Number of mezzanine loans collateralized	2