Real Estate - Dispositions (Details) - Disposal Group, Not Discontinued Operations - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Sales Price	$ 52,654	$ 153,750
Gain on Sale	12,972	81,965
Fund II | Heritage Shops
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Sales Price	30,579
Gain on Sale	6,539
Fund III | Cortlandt Towne Center
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Sales Price	22,075	107,250
Gain on Sale	$ 6,433	65,393
Fund III | Heritage Shops
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Sales Price		46,500
Gain on Sale		$ 16,572