Investments in and Advances to Unconsolidated Affiliates - Fund Investments - Additional Information (Details)					3 Months Ended
	Aug. 29, 2018 USD ($) property	Jun. 29, 2018 USD ($) property	May 15, 2018 USD ($)	Jan. 18, 2018 USD ($) property	Mar. 31, 2019 USD ($) property
Schedule of Equity Method Investments [Line Items]
Number of retail properties | property					174
Proceeds from the disposition of properties, net					$ 9,779,000
Fund III's Storage Post venture
Schedule of Equity Method Investments [Line Items]
Distribution from cost method investment			$ 3,200,000
Cost method investments			0
Fund III's Storage Post venture | Partnership Interest
Schedule of Equity Method Investments [Line Items]
Distribution from cost method investment			$ 800,000
Fund IV | Disposed of by sale | Broughton St. Portfolio Savannah, GA
Schedule of Equity Method Investments [Line Items]
Number of retail properties | property	1			2
Proceeds from the disposition of properties, net	$ 2,100,000			$ 8,000,000
Gain (loss) on disposal	(300,000)			(400,000)
Fund IV | Partnership Interest | Disposed of by sale | Broughton St. Portfolio Savannah, GA
Schedule of Equity Method Investments [Line Items]
Gain (loss) on disposal				$ 0
Fund IV | Partnership Interest | Disposed of by sale | Broughton St. Portfolio Savannah, GA | Maximum
Schedule of Equity Method Investments [Line Items]
Gain (loss) on disposal	$ (100,000)
Fund IV's Broughton Street Portfolio venture
Schedule of Equity Method Investments [Line Items]
Number of retail properties | property		2
Losses on cost method investments		$ 1,000,000
Fund IV's Broughton Street Portfolio venture | Partnership Interest | Maximum
Schedule of Equity Method Investments [Line Items]
Losses on cost method investments		$ 100,000