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, 2019 USD ($) ft²	Dec. 31, 2018 USD ($) a	Dec. 31, 2017 USD ($)	Mar. 31, 2018 USD ($)
Gross Leasable Area | ft²	[1]	290
Equity Method Investments		$ 578,100	$ 570,900
Proceeds from Equity Method Investment, Distribution		93,877	104,626	$ 58,189
Business Combination, Consideration Transferred, Total		43,158
Other Liabilities, Total		346,183	$ 385,328
Accumulated Foreign Currency Adjustment Attributable to Noncontrolling Interest [Member] | CANADA
Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Tax, Total				(4,800)
Prudential Investment Program [Member]
Tangible Asset Impairment Charges, Total		$ 29,900
All Equity Method Investments [Member]
Number of Real Estate Properties		98	109
Gross Leasable Area		21,300	23.2
Kim Pru and Kim Pru II [Member]
Number of Joint Ventures		4
Number Of Accounts		4
Equity Method Investment, Ownership Percentage	[2],[3]	15.00%
Investment in Unconsolidated Property, Unconsolidated 2017 [Member]
Equity Method Investments			$ 62,400		$ 62,400
Equity Method Investment, Ownership Percentage			54.80%
Prudential Investment Program [Member]
Tangible Asset Impairment Charges, Total		$ 3,700
Other Joint Venture Programs [Member]
Proceeds from Equity Method Investment, Distribution			$ 3,600
Impairment of Long-Lived Assets to be Disposed of			5,200	$ 3,400
Other Liabilities, Total		$ 3,500	$ 2,500
Real Estate Joint Ventures [Member] | Operating Properties [Member]
Number of Real Estate Properties, Interest Disposed of or Transferred		9	11	13
Equity Method Investment, Sales Price		$ 247,400	$ 213,500	$ 180,800
Equity Method Investment, Realized Gain (Loss) on Disposal, Total		$ 14,400	$ 18,500	$ 7,500
Number of Real Estate Properties, Remaining Interest Acquired				3
Business Combination, Consideration Transferred, Total				$ 320,100
KIR [Member]
Equity Method Investment, Ownership Percentage		48.60%

[1] Gross leasable area ("GLA")

[2] Represents four separate joint ventures, with four separate accounts managed by Prudential Global Investment Management. One of these ventures disposed of all its properties during 2019.

[3] The Company manages these joint venture investments and, where applicable, earns acquisition fees, leasing commissions, property management fees, asset management fees and construction management fees.