Note 5 - Investments In and Advances to Real Estate Joint Ventures (Details Textual) $ in Thousands, ft² in Millions, a in Millions		3 Months Ended
		Mar. 31, 2018 USD ($) a	Mar. 31, 2017 USD ($)	Jan. 01, 2018 USD ($)	Dec. 31, 2017 USD ($) ft²
Deferred Gain on Sale of Property					$ 6,900
Equity Method Investments		$ 560,068			483,861
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		118			118
Gross Leasable Area		24.1			23.5
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
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
Real Estate Joint Ventures [Member] | Operating Properties [Member]
Number of Real Estate Properties, Interest Disposed of or Transferred		2	5
Equity Method Investment, Sales Price		$ 17,100	$ 47,700
Equity Method Investment, Realized Gain (Loss) on Disposal, Total		$ 2,100	$ 900
Number of Real Estate Properties, Remaining Interest Acquired			2
Business Combination, Consideration Transferred, Total			$ 15,400

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