Related Party Transactions and Investments in Non-Consolidated Entities - Equity in losses of investment in non-consolidated REITs (Details) - USD ($)	1 Months Ended		3 Months Ended		6 Months Ended
	May 31, 2009	Dec. 31, 2007	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Sponsored REITs
Equity in losses of non-consolidated REITs			$ 282,000	$ 201,000	$ 387,000	$ 598,000
Impairment charge					309,000
Distributions received from non-consolidated REITs
Distributions from non-consolidated REITs					710,000	691,000
East Wacker
Sponsored REITs
Equity in losses of non-consolidated REITs					26,000	251,000
Preferred shares purchased		965.75
Percentage of outstanding preferred shares purchased		43.70%
Net cost of preferred shares purchased		$ 82,813,000
Offering price of preferred shares purchased		96,575,000
Commissions excluded		7,726,000
Loan fees excluded		5,553,000
Acquisition fees excluded		$ 483,000
Grand Boulevard
Sponsored REITs
Equity in losses of non-consolidated REITs					$ 52,000	$ 347,000
Preferred shares purchased	175.5
Percentage of outstanding preferred shares purchased	27.00%
Net cost of preferred shares purchased	$ 15,049,000
Offering price of preferred shares purchased	17,550,000
Commissions excluded	1,404,000
Loan fees excluded	1,009,000
Acquisition fees excluded	$ 88,000