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	9 Months Ended
	Apr. 03, 2019	Feb. 02, 2019	Sep. 27, 2018	Sep. 24, 2018	Aug. 17, 2018	Jul. 19, 2018	May 31, 2009	Dec. 31, 2007	Sep. 30, 2018	Sep. 30, 2018	Sep. 30, 2019
Sponsored REITs
Equity in income (loss)									$ 7,180,000	$ 6,793,000
Impairment charge										(309,000)
Amount received										74,931,000
Distributions received from non-consolidated REITs
Equity Method Investment Distribution in Excess of Earnings										710,000
East Wacker
Sponsored REITs
Equity in income (loss)										7,209,000
Preferred shares purchased								965.75
Percentage of outstanding preferred shares purchased								43.70%
Liquidating distribution receivable				$ 70,000,000
Gain (loss) on liquidation				$ 7,100,000
Amount received	$ 1,000,000		$ 69,000,000
Grand Boulevard
Sponsored REITs
Equity in income (loss)										$ (107,000)
Preferred shares purchased							175.5
Percentage of outstanding preferred shares purchased							27.00%
Liquidating distribution receivable						$ 6,200,000
Gain (loss) on liquidation						$ (100,000)
Amount received		$ 200,000			$ 5,900,000
Beneficial interest											$ 100,000