Investments in and Advances to Unconsolidated Affiliates - Fund Investments (Details) - USD ($) $ in Thousands	1 Months Ended				3 Months Ended	12 Months Ended
	Dec. 31, 2016	Jan. 31, 2016	Sep. 30, 2015	Apr. 30, 2015	Jun. 30, 2015	Dec. 31, 2016	Dec. 31, 2015	Mar. 31, 2016
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage								65.00%
Purchase Price						$ 756,842	$ 451,220
Mortgages [Member]
Schedule of Equity Method Investments [Line Items]
Repayments of debt						292,300
Fund III [Member] | White City Shopping Center [Member]
Schedule of Equity Method Investments [Line Items]
Consideration received				$ 96,800
Gain (loss) on disposal				$ 16,200	$ 17,100
Fund III [Member] | Cortlandt Towne Center [Member]
Schedule of Equity Method Investments [Line Items]
Consideration received	$ 57,800	$ 107,300				57,800
Gain (loss) on disposal	$ 36,000	$ 65,400
Percentage of disposition	35.00%	65.00%
Proceeds from sale of equity method investments	$ 25,200
Fund III [Member] | Cortlandt Towne Center [Member] | Mortgages [Member]
Schedule of Equity Method Investments [Line Items]
Repayments of debt	$ 32,600
Fund IV [Member]
Schedule of Equity Method Investments [Line Items]
Purchase Price						$ 237,250	$ 146,177
Fund IV [Member] | 650 Bald Hill Road [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage	90.00%		90.00%			90.00%
Purchase Price			$ 9,200
Partnership Interest [Member] | Fund III [Member] | Cortlandt Towne Center [Member]
Schedule of Equity Method Investments [Line Items]
Gain (loss) on disposal	$ 8,800