Investments in Unconsolidated Real Estate Ventures - Schedule of Equity in Earnings of Unconsolidated Real Estate Ventures (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Schedule of Equity Method Investments [Line Items]
Equity in earnings	$ 15,331	$ 12,895	$ 12,351
PREXR
Schedule of Equity Method Investments [Line Items]
Equity in earnings	3,562	2,919	4,041
SP I
Schedule of Equity Method Investments [Line Items]
Equity in earnings	2,684	2,380	1,951
PRISA
Schedule of Equity Method Investments [Line Items]
Equity in earnings	33	0	0
ESW II
Schedule of Equity Method Investments [Line Items]
Equity in earnings	2,430	1,912	1,013
Clarendon
Schedule of Equity Method Investments [Line Items]
Equity in earnings	1,210	174	145
ESS PRISA II LLC Joint Venture
Schedule of Equity Method Investments [Line Items]
Equity in earnings	1,033	614	569
ESW
Schedule of Equity Method Investments [Line Items]
Equity in earnings	2,502	2,269	1,875
ESNPS
Schedule of Equity Method Investments [Line Items]
Equity in earnings	918	823	633
Other Minority Owned Properties
Schedule of Equity Method Investments [Line Items]
Equity in earnings	$ 959	$ 1,804	$ 2,124