Investments in Real Estate Partnerships - Schedule of Acquisitions by Real Estate Partnerships (Details) ratio in Thousands	12 Months Ended
Dec. 31, 2015 USD ($) property	Dec. 31, 2014 USD ($) property	Dec. 31, 2013 USD ($) property
Business Acquisition [Line Items]
Proceeds from sale of real estate investments	$ 108,822,000	$ 118,787,000	$ 212,632,000
Gain on sale of real estate	2,766,000	28,856,000	15,695,000
Equity in income of investments in real estate partnerships (note 4)	22,508,000	31,270,000	31,718,000
Investments in real estate partnerships (note 4)	306,206,000	333,167,000
Columbia Regency Partners II, LLC [Member]
Business Acquisition [Line Items]
Equity in income of investments in real estate partnerships (note 4)	$ 755,000	$ 233,000
Equity Method Investment, Ownership Percentage	0.00%	0.00%
Investments in real estate partnerships (note 4)	$ 8,496,000	$ 9,343,000
GRI - Regency, LLC [Member]
Business Acquisition [Line Items]
Equity in income of investments in real estate partnerships (note 4)	$ 18,148,000	$ 13,727,000
Equity Method Investment, Ownership Percentage	0.00%	0.00%
Investments in real estate partnerships (note 4)	$ 220,099,000	$ 247,175,000
Other Investments in Real Estate Partnerships [Member]
Business Acquisition [Line Items]
Equity in income of investments in real estate partnerships (note 4)	$ 1,857,000	$ 13,338,000
Equity Method Investment, Ownership Percentage	0.00%	0.00%
Investments in real estate partnerships (note 4)	$ 32,371,000	$ 34,459,000
RegCal, LLC [Member]
Business Acquisition [Line Items]
Equity in income of investments in real estate partnerships (note 4)	$ 576,000	$ 966,000
Equity Method Investment, Ownership Percentage	0.00%	0.00%
Investments in real estate partnerships (note 4)	$ 17,967,000	$ 13,354,000
Unconsolidated Properties [Member]
Business Acquisition [Line Items]
Proceeds from sale of real estate investments	39,459,000	88,106,000	145,295,000
Corporate Joint Venture [Member]
Business Acquisition [Line Items]
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
Payments to Acquire Businesses, Gross	0	$ 43,000,000
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
Payments to Acquire Businesses, Gross		$ 43,000,000
Corporate Joint Venture [Member] \| Columbia Regency Partners II, 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	108,822,000	$ 118,787,000	212,632,000
Equity in income of investments in real estate partnerships (note 4)	22,508,000	31,270,000	31,718,000
Mortgage loans assumed for the acquisition of real estate	42,799,000	103,187,000	0
Investments in real estate partnerships (note 4)	306,206,000	333,167,000
Gain on sale of real estate investments [Member]
Business Acquisition [Line Items]
Equity in income of investments in real estate partnerships (note 4)	$ 1,108,000	$ 13,615,000	$ 3,847,000
Operating Segments [Member]
Business Acquisition [Line Items]
Number of Real Estate Properties Sold \| property	5	11	12
Operating Segments [Member] \| Unconsolidated Properties [Member]
Business Acquisition [Line Items]
Number of Real Estate Properties Sold \| property	2	6	15
Land [Member]
Business Acquisition [Line Items]
Number of Real Estate Properties Sold \| property	2	6	10
Land [Member] \| Unconsolidated Properties [Member]
Business Acquisition [Line Items]
Number of Real Estate Properties Sold \| property	0	2	3

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With respect to a business combination completed during the period, this element provides a description of the business, other than the name, which may include the industry, size, products and other important information.

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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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This item represents the entity's proportionate share for the period of the net income (loss) of its investee (such as unconsolidated subsidiaries and joint ventures) to which the equity method of accounting is applied. This item includes income or expense related to stock-based compensation based on the investor's grant of stock to employees of an equity method investee.

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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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The amount of debt that an Entity assumes in acquiring a business or in consideration for an asset received in a noncash (or part noncash) acquisition. Noncash is defined as transactions during a period that affect recognized assets or liabilities but that do not result in cash receipts or cash payments in the period. "Part noncash" refers to that portion of the transaction not resulting in cash receipts or cash payments in the period.

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The cash outflow associated with the acquisition of business during the period. The cash portion only of the acquisition price.

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