Investments in Real Estate Partnerships - Schedule of Acquisitions by Real Estate Partnerships (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Calhoun Commons [Member]
Business Acquisition [Line Items]
Business Acquisition, Effective Date of Acquisition		Jul. 01, 2011
Business Acquisition, Name of Acquired Entity		Calhoun Commons
Business Acquisition Location, City and State		Minneapolis, MN
Rockridge Center [Member]
Business Acquisition [Line Items]
Business Acquisition, Effective Date of Acquisition		Aug. 08, 2011
Business Acquisition, Name of Acquired Entity		Rockridge Center
Business Acquisition Location, City and State		Plymouth, MN
GRI - Regency, LLC [Member]
Business Acquisition [Line Items]
Equity Method Investment, Ownership Percentage	40.00%	40.00%
RegCal, LLC [Member]
Business Acquisition [Line Items]
Equity Method Investment, Ownership Percentage	25.00%	25.00%
Columbia Regency Partners II, LLC [Member]
Business Acquisition [Line Items]
Equity Method Investment, Ownership Percentage	20.00%	20.00%
Corporate Joint Venture [Member]
Business Acquisition [Line Items]
Business Acquisition, Cost of Acquired Entity, Purchase Price	$ 150,800	$ 41,520
Mortgage loans assumed for the acquisition of real estate	76,313	22,511
Acquired Finite-lived Intangible Asset, Amount	8,002	4,246
Acquired Finite Lived Intangible Liability Amount	5,062	2,362
Corporate Joint Venture [Member] | Lake Grove Commons [Member]
Business Acquisition [Line Items]
Business Acquisition, Effective Date of Acquisition	Jan. 17, 2012
Business Acquisition, Name of Acquired Entity	Lake Grove Commons
Business Acquisition Location, City and State	Lake Grove, NY
Equity Method Investment, Ownership Percentage	40.00%
Business Acquisition, Cost of Acquired Entity, Purchase Price	72,500
Mortgage loans assumed for the acquisition of real estate	31,813
Acquired Finite-lived Intangible Asset, Amount	5,397
Acquired Finite Lived Intangible Liability Amount	4,342
Corporate Joint Venture [Member] | Applewood Village Shops [Member]
Business Acquisition [Line Items]
Business Acquisition, Effective Date of Acquisition	Nov. 28, 2012
Business Acquisition, Name of Acquired Entity	Applewood Village Shops
Business Acquisition Location, City and State	Wheat Ridge, CO
Equity Method Investment, Ownership Percentage	40.00%
Business Acquisition, Cost of Acquired Entity, Purchase Price	3,700
Mortgage loans assumed for the acquisition of real estate	0
Acquired Finite-lived Intangible Asset, Amount	363
Acquired Finite Lived Intangible Liability Amount	34
Corporate Joint Venture [Member] | Village Plaza [Member]
Business Acquisition [Line Items]
Business Acquisition, Effective Date of Acquisition	Dec. 19, 2012
Business Acquisition, Name of Acquired Entity	Village Plaza
Business Acquisition Location, City and State	Chapel Hill, NC
Equity Method Investment, Ownership Percentage	20.00%
Business Acquisition, Cost of Acquired Entity, Purchase Price	19,200
Mortgage loans assumed for the acquisition of real estate	0
Acquired Finite-lived Intangible Asset, Amount	2,242
Acquired Finite Lived Intangible Liability Amount	686
Corporate Joint Venture [Member] | Shops at Erwin Mill [Member]
Business Acquisition [Line Items]
Business Acquisition, Effective Date of Acquisition	Dec. 28, 2012
Business Acquisition, Name of Acquired Entity	Phillips Place
Business Acquisition Location, City and State	Charlotte, NC
Equity Method Investment, Ownership Percentage	50.00%
Business Acquisition, Cost of Acquired Entity, Purchase Price	55,400
Mortgage loans assumed for the acquisition of real estate	44,500
Acquired Finite-lived Intangible Asset, Amount	0
Acquired Finite Lived Intangible Liability Amount	0
Corporate Joint Venture [Member] | Calhoun Commons [Member]
Business Acquisition [Line Items]
Equity Method Investment, Ownership Percentage		25.00%
Business Acquisition, Cost of Acquired Entity, Purchase Price		21,020
Mortgage loans assumed for the acquisition of real estate		6,052
Acquired Finite-lived Intangible Asset, Amount		2,130
Acquired Finite Lived Intangible Liability Amount		303
Corporate Joint Venture [Member] | Rockridge Center [Member]
Business Acquisition [Line Items]
Equity Method Investment, Ownership Percentage		20.00%
Business Acquisition, Cost of Acquired Entity, Purchase Price		20,500
Mortgage loans assumed for the acquisition of real estate		16,459
Acquired Finite-lived Intangible Asset, Amount		2,116
Acquired Finite Lived Intangible Liability Amount		$ 2,059
Corporate Joint Venture [Member] | GRI - Regency, LLC [Member] | Lake Grove Commons [Member]
Business Acquisition [Line Items]
Business Acquisition, Description of Acquired Entity	GRIR
Corporate Joint Venture [Member] | GRI - Regency, LLC [Member] | Applewood Village Shops [Member]
Business Acquisition [Line Items]
Business Acquisition, Description of Acquired Entity	GRIR
Corporate Joint Venture [Member] | RegCal, LLC [Member] | Calhoun Commons [Member]
Business Acquisition [Line Items]
Business Acquisition, Description of Acquired Entity		RegCal
Corporate Joint Venture [Member] | Columbia Regency Partners II, LLC [Member] | Village Plaza [Member]
Business Acquisition [Line Items]
Business Acquisition, Description of Acquired Entity	Columbia II
Corporate Joint Venture [Member] | Columbia Regency Partners II, LLC [Member] | Rockridge Center [Member]
Business Acquisition [Line Items]
Business Acquisition, Description of Acquired Entity		Columbia II
Corporate Joint Venture [Member] | Johnny Harris [Member] | Shops at Erwin Mill [Member]
Business Acquisition [Line Items]
Business Acquisition, Description of Acquired Entity	Other