Note 7 - Investment In and Advances to Real Estate Joint Ventures (Details Textual) ft² in Thousands, $ in Thousands, a in Millions		12 Months Ended
		Dec. 31, 2018 USD ($) a	Dec. 31, 2017 USD ($) ft²	Dec. 31, 2016 USD ($)	Mar. 31, 2018 USD ($)	Jan. 01, 2018 USD ($)
Gross Leasable Area | ft²	[1]		2,875
Deferred Gain on Sale of Property			$ 6,900
Equity Method Investments		$ 570,922	483,861
Proceeds from Equity Method Investment, Distribution		104,626	58,189	$ 90,589
Business Combination, Consideration Transferred, Total			688,326
Other Liabilities, Total		$ 385,328	431,915
Accumulated Foreign Currency Adjustment Attributable to Noncontrolling Interest [Member] | CANADA
Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Tax, Total			(4,800)
Accounting Standards Update 2017-05 [Member]
Cumulative Effect of New Accounting Principle in Period of Adoption	[2]		$ 8,098
All Equity Method Investments [Member]
Number of Real Estate Properties		109	118
Gross Leasable Area		23.2	23,500
Kim Pru and Kim Pru II [Member]
Number of Joint Ventures		4
Number Of Accounts		4
Kim Pru [Member]
Number of Joint Ventures		3
Kim Pru II [Member]
Deferred Gain on Sale of Property			$ 5,100
Other Joint Venture Programs [Member]
Deferred Gain on Sale of Property			1,800
Proceeds from Equity Method Investment, Distribution		$ 3,600
Impairment of Long-Lived Assets to be Disposed of		5,200	3,400
Other Liabilities, Total		2,500	$ 2,100
Other Joint Venture Programs [Member] | Accounting Standards Update 2017-05 [Member]
Cumulative Effect of New Accounting Principle in Period of Adoption						$ 6,900
Investment in Unconsolidated Property, Unconsolidated 2017 [Member]
Equity Method Investments		$ 62,400			$ 62,400
Real Estate Joint Ventures [Member] | Operating Properties [Member]
Number of Real Estate Properties, Interest Disposed of or Transferred		11	13	45
Equity Method Investment, Sales Price		$ 213,500	$ 180,800	$ 1,100,000
Equity Method Investment, Realized Gain (Loss) on Disposal, Total		$ 18,500	$ 7,500	$ 151,200
Number of Real Estate Properties, Remaining Interest Acquired			3	9
Business Combination, Consideration Transferred, Total			$ 320,100	$ 590,100
Real Estate Joint Ventures [Member] | Land Parcels [Member]
Number of Real Estate Properties, Interest Disposed of or Transferred				1
Real Estate Joint Ventures [Member] | Development Properties [Member]
Number of Real Estate Properties, Remaining Interest Acquired				1

[1] Gross leasable area ("GLA")

[2] Represents the impact of change in accounting principles for its respective Accounting Standard Updates ("ASU"). See Footnote 1 of the Notes to Consolidated Financial Statements for additional disclosure.