Investments in Real Estate Partnerships - Schedule of Acquisitions by Real Estate Partnerships (Details) (USD $)	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Business Acquisition [Line Items]
Proceeds from sale of real estate investments	$ 118,787,000	$ 212,632,000	$ 352,707,000
Gain on sale of real estate	28,856,000	15,695,000	40,437,000
Equity in income of investments in real estate partnerships (note 4)	31,270,000	31,718,000	23,807,000
Investments in real estate partnerships (note 4)	333,167,000	358,849,000
Columbia Regency Partners II, LLC [Member]
Business Acquisition [Line Items]
Equity in income of investments in real estate partnerships (note 4)	233,000	1,274,000
Equity Method Investment, Ownership Percentage	0.00%	0.00%
Investments in real estate partnerships (note 4)	9,343,000	8,797,000
BRE Throne Holdings LLC (BRET) [Member]
Business Acquisition [Line Items]
Equity in income of investments in real estate partnerships (note 4)		4,499,000
Equity Method Investment, Ownership Percentage		0.00%
Proceeds from Sale of Real Estate		321,000,000
Investments in real estate partnerships (note 4)		0
GRI - Regency, LLC [Member]
Business Acquisition [Line Items]
Equity in income of investments in real estate partnerships (note 4)	13,727,000	12,789,000
Equity Method Investment, Ownership Percentage	0.00%	0.00%
Investments in real estate partnerships (note 4)	247,175,000	250,118,000
Other Investments in Real Estate Partnerships [Member]
Business Acquisition [Line Items]
Equity in income of investments in real estate partnerships (note 4)	13,311,000	2,146,000
Equity Method Investment, Ownership Percentage	0.00%	0.00%
Investments in real estate partnerships (note 4)	34,459,000	47,761,000
RegCal, LLC [Member]
Business Acquisition [Line Items]
Equity in income of investments in real estate partnerships (note 4)	966,000	332,000
Equity Method Investment, Ownership Percentage	0.00%	0.00%
Investments in real estate partnerships (note 4)	13,354,000	15,576,000
Unconsolidated Properties [Member]
Business Acquisition [Line Items]
Proceeds from sale of real estate investments	88,106,000	145,295,000	119,275,000
Corporate Joint Venture [Member]
Business Acquisition [Line Items]
Mortgage loans assumed for the acquisition of real estate	0	7,496,000
Acquired Finite-lived Intangible Asset, Amount	7,604,000	8,438,000
Acquired Finite Lived Intangible Liability Amount	3,487,000	332,000
Significant Acquisitions and Disposals, Acquisition Costs or Sale Proceeds	43,000,000	13,600,000
Corporate Joint Venture [Member] \| Shoppes of Burnt Mills [Member]
Business Acquisition [Line Items]
Business Acquisition, Effective Date of Acquisition		Jul. 23, 2013
Business Acquisition, Name of Acquired Entity		Shoppes of Burnt Mills
Business Acquisition Location, City and State		Silver Spring, MD
Business Acquisition, Property type		Operating
Equity Method Investment, Ownership Percentage		0.00%
Mortgage loans assumed for the acquisition of real estate		7,496,000
Acquired Finite-lived Intangible Asset, Amount		8,438,000
Acquired Finite Lived Intangible Liability Amount		332,000
Significant Acquisitions and Disposals, Acquisition Costs or Sale Proceeds		13,600,000
Corporate Joint Venture [Member] \| Broadway [Member]
Business Acquisition [Line Items]
Business Acquisition, Effective Date of Acquisition	Dec. 30, 2014
Business Acquisition, Name of Acquired Entity	Broadway
Business Acquisition Location, City and State	Seattle, WA
Business Acquisition, Property type	Operating
Equity Method Investment, Ownership Percentage	0.00%
Mortgage loans assumed for the acquisition of real estate	0
Acquired Finite-lived Intangible Asset, Amount	7,604,000
Acquired Finite Lived Intangible Liability Amount	3,487,000
Significant Acquisitions and Disposals, Acquisition Costs or Sale Proceeds	43,000,000
Corporate Joint Venture [Member] \| Columbia Regency Partners II, LLC [Member] \| Shoppes of Burnt Mills [Member]
Business Acquisition [Line Items]
Business Acquisition, Description of Acquired Entity		Columbia II
Corporate Joint Venture [Member] \| GRI - Regency, LLC [Member] \| Broadway [Member]
Business Acquisition [Line Items]
Business Acquisition, Description of Acquired Entity	Columbia II
Partnership Interest [Member]
Business Acquisition [Line Items]
Proceeds from sale of real estate investments	118,787,000	212,632,000	352,707,000
Equity in income of investments in real estate partnerships (note 4)	31,270,000	31,718,000	23,807,000
Mortgage loans assumed for the acquisition of real estate	103,187,000	0	30,467,000
Investments in real estate partnerships (note 4)	333,167,000	358,849,000
Gain on sale of real estate investments [Member]
Business Acquisition [Line Items]
Equity in income of investments in real estate partnerships (note 4)	$ 13,615,000	$ 3,847,000	$ 8,962,000
Operating Segments [Member]
Business Acquisition [Line Items]
Number of Real Estate Properties Sold	11	12	20
Operating Segments [Member] \| Unconsolidated Properties [Member]
Business Acquisition [Line Items]
Number of Real Estate Properties Sold	6	15	7
Land [Member]
Business Acquisition [Line Items]
Number of Real Estate Properties Sold	6	10	7
Land [Member] \| Unconsolidated Properties [Member]
Business Acquisition [Line Items]
Number of Real Estate Properties Sold	2	3	1

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The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

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Total investments in (A) an entity in which the entity has significant influence, but does not have control, (B) subsidiaries that are not required to be consolidated and are accounted for using the equity and or cost method, and (C) an entity in which the reporting entity shares control of the entity with another party or group. Includes long-term advances receivable from a party that is affiliated with the reporting entity by means of direct or indirect ownership.

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Cash received for the sale of real estate that is not part of an investing activity during the current period.

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