Note 5 - Investments In and Advances to Real Estate Joint Ventures (Details Textual) $ in Thousands, ft² in Millions		3 Months Ended	6 Months Ended
		Jun. 30, 2018 USD ($) ft²	Jun. 30, 2018 USD ($) ft²	Jun. 30, 2017 USD ($)	Mar. 31, 2018 USD ($)	Jan. 01, 2018 USD ($)	Dec. 31, 2017 USD ($) ft²
Deferred Gain on Sale of Property							$ 6,900
Equity Method Investments		$ 568,698	$ 568,698				483,861
Proceeds from Equity Method Investment, Distribution			$ 67,005	$ 27,678
Accounting Standards Update 2017-05 [Member]
Cumulative Effect of New Accounting Principle in Period of Adoption	[1]						$ 8,098
All Equity Method Investments [Member]
Number of Real Estate Properties		116	116				118
Gross Leasable Area | ft²		23.9	23.9				23.5
Kim Pru and Kim Pru II [Member]
Number of Joint Ventures		4	4
Number Of Accounts		4	4
Kim Pru [Member]
Number of Joint Ventures		3	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
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		$ 62,400
Real Estate Joint Ventures [Member] | Operating Properties [Member]
Number of Real Estate Properties, Interest Disposed of or Transferred			4	6
Equity Method Investment, Sales Price		$ 37,900	$ 37,900	$ 49,300
Equity Method Investment, Realized Gain (Loss) on Disposal, Total			$ 3,500	$ 100
Number of Real Estate Properties, Remaining Interest Acquired				3
Business Combination, Consideration Transferred, Total				$ 320,100

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