Note 2 - Operating Property Activities (Details) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2015 USD ($)	Sep. 30, 2014 USD ($)	Sep. 30, 2015 USD ($)	Sep. 30, 2014 USD ($)	Feb. 28, 2015	Dec. 31, 2014 USD ($)
Note 2 - Operating Property Activities (Details) [Line Items]
Proceeds from Delayed Tax Exempt Exchange				$ 39,800
Business Combination, Step Acquisition, Equity Interest in Acquiree, Remeasurement Gain		$ 6,342	$ 14,431	146,143	$ 83,773
Payments to Acquire Real Estate				619,622	$ 382,128
Business Combination, Consideration Transferred				1,554,744
Payments to Acquire Additional Interest in Subsidiaries				30,500
Proceeds from Sale of Real Estate				276,300
Gains (Losses) on Sales of Investment Real Estate				86,200
Impairment of Real Estate				2,200
Real Estate Investment Property, Accumulated Depreciation		$ 2,092,375		2,092,375			$ 1,955,406
Operating Expense [Member]
Note 2 - Operating Property Activities (Details) [Line Items]
Impairment of Real Estate				27,900
Operating Expense [Member] | Real Estate, Operating Properties [Member]
Note 2 - Operating Property Activities (Details) [Line Items]
Impairment of Real Estate				2,200
Operating Expense [Member] | Real Estate, Carrying Value Adjustment [Member]
Note 2 - Operating Property Activities (Details) [Line Items]
Impairment of Real Estate				19,600
Operating Expense [Member] | Other Real Estate Investments [Member]
Note 2 - Operating Property Activities (Details) [Line Items]
Impairment of Real Estate				5,300
Operating Expense [Member] | Certain Marketable Securities [Member]
Note 2 - Operating Property Activities (Details) [Line Items]
Impairment of Real Estate				$ 800
Acquired Land [Member]
Note 2 - Operating Property Activities (Details) [Line Items]
Number of Real Estate Properties		4		4
Payments to Acquire Real Estate				$ 37,500
Sold [Member] | Operating Properties [Member]
Note 2 - Operating Property Activities (Details) [Line Items]
Number of Real Estate Properties		74		74
Sold [Member] | Other Property [Member]
Note 2 - Operating Property Activities (Details) [Line Items]
Number of Real Estate Properties		6		6
Elmont Plaza [Member]
Note 2 - Operating Property Activities (Details) [Line Items]
Noncontrolling Interest, Ownership Percentage by Parent							50.00%
Business Combination, Step Acquisition, Equity Interest in Acquiree, Remeasurement Loss				$ 200
Business Combination, Consideration Transferred	[1]			$ 5,758
Kimstone [Member]
Note 2 - Operating Property Activities (Details) [Line Items]
Noncontrolling Interest, Ownership Percentage by Parent							33.30%
Number of Real Estate Properties		39		39		39
Business Combination, Step Acquisition, Equity Interest in Acquiree, Remeasurement Gain				$ 140,000
Business Combination, Consideration Transferred	[2]			1,387,500
Montgomery Plaza [Member]
Note 2 - Operating Property Activities (Details) [Line Items]
Noncontrolling Interest, Ownership Percentage by Parent							20.00%
Business Combination, Step Acquisition, Equity Interest in Acquiree, Remeasurement Gain				6,300
Business Combination, Consideration Transferred	[3]			$ 72,877
Enclosed Mall in Owings Mills, MD [Member]
Note 2 - Operating Property Activities (Details) [Line Items]
Business Acquisition, Percentage of Remaining Interests Acquired		50.00%		50.00%
Business Combination, Consideration Transferred		$ 23,000
Remaining Interest In Joint Ventures [Member]
Note 2 - Operating Property Activities (Details) [Line Items]
Noncontrolling Interest, Period Increase (Decrease)				$ (25,000)
Adjustments to Additional Paid in Capital, Other				5,400
Other Liabilities [Member] | Enclosed Mall in Owings Mills, MD [Member]
Note 2 - Operating Property Activities (Details) [Line Items]
Liability to Purchase Partners Interest		11,500		$ 11,500
Real Estate under Development [Member] | Enclosed Mall in Owings Mills, MD [Member]
Note 2 - Operating Property Activities (Details) [Line Items]
Business Combination, Consideration Transferred		8,400
Operating Real Estate [Member] | Enclosed Mall in Owings Mills, MD [Member]
Note 2 - Operating Property Activities (Details) [Line Items]
Business Combination, Consideration Transferred		$ 14,600
Disposal Group, Held-for-sale or Disposed of by Sale, Not Discontinued Operations [Member]
Note 2 - Operating Property Activities (Details) [Line Items]
Number of Real Estate Properties		3		3
Real Estate Held-for-sale		$ 23,400		$ 23,400
Real Estate Investment Property, Accumulated Depreciation		10,000		10,000
Adjustments for New Accounting Pronouncement [Member]
Note 2 - Operating Property Activities (Details) [Line Items]
Depreciation and Amortization Expense Adjustments				5,800
Rental Income Adjustments				(100)
Preferred Equity Investment [Member]
Note 2 - Operating Property Activities (Details) [Line Items]
Proceeds from Sale of Real Estate				18,700
Gains (Losses) on Sales of Investment Real Estate				0
Preferred Equity Investment [Member] | Mortgage Debt [Member]
Note 2 - Operating Property Activities (Details) [Line Items]
Non-Recourse Debt		$ 16,300		$ 16,300

[1] The Company acquired from its partner the remaining ownership interest in a property that was held in a joint venture in which the Company had a 50.0%noncontrolling interest. The Company evaluated this transaction pursuant to the FASB's Consolidation guidance and as a result, recognized a loss on change in control of interest of $0.2 million resulting from the fair value adjustment associated with the Company's previously held equity interest, which is reflected in the purchase price above in Other.

[2] The Company acquired from its partner the remaining ownership interest in 39 properties that were held in a joint venture in which the Company had a 33.3%noncontrolling interest. The Company evaluated this transaction pursuant to the FASB's Consolidation guidance and as a result, recognized a gain on change in control of interest of $140.0 million resulting from the fair value adjustment associated with the Company's previously held equity interest, which is reflected in the purchase price above in Other.

[3] The Company acquired from its partner the remaining ownership interest in a property that was held in a joint venture in which the Company had a 20.0%noncontrolling interest. The Company evaluated this transaction pursuant to the FASB's Consolidation guidance and as a result, recognized a gain on change in control of interest of $6.3 million resulting from the fair value adjustment associated with the Company's previously held equity interest, which is reflected in the purchase price above in Other.