Note 5 - Investments In and Advances to Real Estate Joint Ventures (Details Textual) ft² in Thousands, $ in Thousands		9 Months Ended
		Sep. 30, 2019 USD ($) ft²	Sep. 30, 2018 USD ($)	Dec. 31, 2018 ft²
Gross Leasable Area | ft²	[1]	125
Proceeds from Equity Method Investment, Distribution		$ 78,940	$ 80,900
All Equity Method Investments [Member]
Number of Real Estate Properties		101		109
Gross Leasable Area | ft²		21,600		23,200
Real Estate Joint Ventures [Member] | Operating Properties [Member]
Number of Real Estate Properties, Interest Disposed of or Transferred		1	1
Equity Method Investment, Sales Price		$ 240,900	$ 48,400
Impairment of Long-Lived Assets to be Disposed of		$ 13,700	6,100
Other Joint Venture Programs [Member]
Proceeds from Equity Method Investment, Distribution			$ 3,600

[1] Gross leasable area ("GLA")