Real Estate Investments Business Acquisitions (Details) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2012
Business Acquisition [Line Items]
Business Acquisition, Cost of Acquired Entity, Purchase Price	$ 84,619
Business Acquisition, Purchase Price Allocation, Liabilities Assumed	43,523
Acquired Finite-lived Intangible Asset, Amount	7,369
Acquired Finite Lived Intangible Liability, Amount	4,434
Unconsolidated Properties [Member] | Lake Grove [Member] [Member]
Business Acquisition [Line Items]
Business Acquisition, Effective Date of Acquisition	1/17/2012
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
Business Acquisition, Purchase Price Allocation, Liabilities Assumed	31,813
Acquired Finite-lived Intangible Asset, Amount	5,397
Acquired Finite Lived Intangible Liability, Amount	4,342
Consolidated Entities [Member] | Erwin Square [Member]
Business Acquisition [Line Items]
Business Acquisition, Effective Date of Acquisition	5/31/2012
Business Acquisition, Name of Acquired Entity	Erwin Square
Business Acquisition Location, City and State	Durham, NC
Equity Method Investment, Ownership Percentage	55.00%
Business Acquisition, Cost of Acquired Entity, Purchase Price	358
Business Acquisition, Purchase Price Allocation, Liabilities Assumed	0
Acquired Finite-lived Intangible Asset, Amount	0
Acquired Finite Lived Intangible Liability, Amount	0
Consolidated Entities [Member] | Grand Ridge Plaza [Member]
Business Acquisition [Line Items]
Business Acquisition, Effective Date of Acquisition	6/21/2012
Business Acquisition, Name of Acquired Entity	Grand Ridge Plaza
Business Acquisition Location, City and State	Issaquah, WA
Equity Method Investment, Ownership Percentage	100.00%
Business Acquisition, Cost of Acquired Entity, Purchase Price	11,761
Business Acquisition, Purchase Price Allocation, Liabilities Assumed	11,710
Acquired Finite-lived Intangible Asset, Amount	1,972
Acquired Finite Lived Intangible Liability, Amount	$ 92