Organization, Basis of Presentation and Summary of Significant Accounting Policies (Details)	3 Months Ended								12 Months Ended
	Dec. 31, 2016 USD ($) property	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Sep. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)	Mar. 31, 2015 USD ($)	Dec. 31, 2016 USD ($) segment property	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Organization, Consolidation and Presentation of Financial Statements [Line Items]
Number of reporting units | segment									3
Rental income									$ 152,814,000	$ 158,632,000	$ 145,103,000
Depreciation and amortization									70,011,000	60,751,000	49,645,000
Interest expense									34,645,000	37,297,000	39,426,000
Equity in earnings and gains of unconsolidated affiliates									39,449,000	37,330,000	111,578,000
Net income	$ 34,236,000	$ 326,000	$ 26,155,000	$ 73,875,000	$ 7,871,000	$ 18,104,000	$ 85,458,000	$ 38,537,000	134,592,000	149,970,000	152,146,000
Net income for the period January 1 through December 31, 2015	14,415,000	$ (5,786,000)	$ 8,237,000	$ 44,950,000	(1,019,000)	$ 4,328,000	$ 58,963,000	$ 21,990,000	61,816,000	84,262,000	81,082,000
Noncontrolling interests	589,548,000				420,866,000				589,548,000	420,866,000
Impairment of asset									0	5,000,000	0
Deferred rent receivables, net	31,700,000				31,300,000				31,700,000	31,300,000
Allowance for doubtful accounts receivable	$ 5,700,000				7,500,000				$ 5,700,000	7,500,000
Required distribution rate to maintain REIT status (in percent)	90.00%								90.00%
Capitalized internal leasing costs	$ 1,100,000				1,400,000				$ 1,100,000	1,400,000	900,000
Minimum [Member] | Building [Member]
Organization, Consolidation and Presentation of Financial Statements [Line Items]
Property, plant and equipment, useful life (In Years)									30 years
Minimum [Member] | Furniture and Fixtures [Member]
Organization, Consolidation and Presentation of Financial Statements [Line Items]
Property, plant and equipment, useful life (In Years)									5 years
Maximum [Member] | Building [Member]
Organization, Consolidation and Presentation of Financial Statements [Line Items]
Property, plant and equipment, useful life (In Years)									40 years
Maximum [Member] | Furniture and Fixtures [Member]
Organization, Consolidation and Presentation of Financial Statements [Line Items]
Property, plant and equipment, useful life (In Years)									20 years
Out-of-period Adjustments [Member]
Organization, Consolidation and Presentation of Financial Statements [Line Items]
Rental income									$ (2,100,000)
Depreciation and amortization									1,700,000
Interest expense									700,000
Equity in earnings and gains of unconsolidated affiliates									200,000
Net income	(4,200,000)
Net income for the period January 1 through December 31, 2015	(1,600,000)
Noncontrolling interests	$ (35,700,000)				$ (31,800,000)				$ (35,700,000)	$ (31,800,000)
Operating Partnership, as General Partner or Managing Member [Member]
Organization, Consolidation and Presentation of Financial Statements [Line Items]
Equity Interest Held By Operating Partnership									95.00%	95.00%
Remaining funds rate of distribution to operating partnership (in percent)	20.00%								20.00%
Equity in earnings and gains of unconsolidated affiliates									$ 39,449,000	$ 37,330,000	111,578,000
Institutional Investors [Member]
Organization, Consolidation and Presentation of Financial Statements [Line Items]
Remaining funds rate of distribution to all partners (in percent)	80.00%								80.00%
Core Portfolio [Member]
Organization, Consolidation and Presentation of Financial Statements [Line Items]
Number of retail properties | property	117								117
Properties owned percentage	100.00%								100.00%
Depreciation and amortization									$ 54,582,000	46,223,000	35,875,000
Interest expense									27,435,000	27,945,000	27,024,000
Equity in earnings and gains of unconsolidated affiliates									3,774,000	1,169,000	(77,000)
Net income									32,370,000	34,757,000	41,526,000
Net income for the period January 1 through December 31, 2015									$ 3,411,000	140,000	3,222,000
Impairment of asset										5,000,000
Opportunity Funds
Organization, Consolidation and Presentation of Financial Statements [Line Items]
Number of retail properties | property	65								65
Depreciation and amortization									$ 15,429,000	14,528,000	13,770,000
Interest expense									7,210,000	9,352,000	12,402,000
Equity in earnings and gains of unconsolidated affiliates									35,675,000	36,161,000	111,655,000
Net income									116,936,000	129,169,000	123,351,000
Net income for the period January 1 through December 31, 2015									$ 58,405,000	84,122,000	$ 77,860,000
Impairment of asset										0
Core Portfolio and Opportunity Funds [Member]
Organization, Consolidation and Presentation of Financial Statements [Line Items]
Number of retail properties | property	182								182
Non-Recourse Mortgage [Member]
Organization, Consolidation and Presentation of Financial Statements [Line Items]
Borrowings, amount	$ 26,300,000.0								$ 26,300,000.0
Brandywine Portfolio [Member]
Organization, Consolidation and Presentation of Financial Statements [Line Items]
Impairment of asset										$ 5,000,000
Brandywine Portfolio [Member] | Operating Partnership, as General Partner or Managing Member [Member]
Organization, Consolidation and Presentation of Financial Statements [Line Items]
Impairment of asset									$ 1,100,000