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Summary of Significant Accounting Policies - Narrative (Details) - USD ($)
$ in Thousands
3 Months Ended 9 Months Ended
Jan. 01, 2018
Sep. 30, 2018
Sep. 30, 2017
Sep. 30, 2018
Sep. 30, 2017
Dec. 31, 2017
Mar. 31, 2017
Schedule of Equity Method Investments [Line Items]              
Cumulative effect adjustment to equity   $ 5,071,168   $ 5,071,168   $ 5,301,005  
RIDEA II              
Schedule of Equity Method Investments [Line Items]              
Investment ownership percentage   40.00%   40.00%     40.00%
Equity method investments $ 121,000            
ASU 2014-09 | Difference between Revenue Guidance in Effect before and after Topic 606              
Schedule of Equity Method Investments [Line Items]              
Cumulative effect adjustment to equity 79,000            
Impairment charge 30,000            
ASU 2014-09 | Difference between Revenue Guidance in Effect before and after Topic 606 | RIDEA II              
Schedule of Equity Method Investments [Line Items]              
Fair value of equity method investments $ 107,000            
Ancillary service revenue | ASU 2014-09              
Schedule of Equity Method Investments [Line Items]              
Tenant recoveries and Resident fees and services   $ 10,000 $ 9,000 $ 30,000 $ 28,000