Note 4 - Real Estate Under Development (Details Textual) ft² in Thousands		12 Months Ended
		Dec. 31, 2016 USD ($) ft²		Dec. 31, 2015 USD ($) ft²		Dec. 31, 2014 USD ($)
Gross Leasable Area | ft²	[1]	2,665		7,519
Real Estate Investment Property, Net		$ 9,729,783,503		$ 9,453,489,000
Payments to Acquire Businesses, Gross		255,910,000	[2]	712,055,000	[3]
Payments to Acquire Real Estate		$ 203,190,000		$ 661,423,000		$ 384,828,000
Real Estate Under Development [Member]
Number of Real Estate Properties		6
Gross Leasable Area | ft²		2,200
Real Estate Investment Property, Net		$ 514,000,000
Business Combination, Step Acquisition, Equity Interest in Acquiree, Percentage		55.00%
Payments to Acquire Businesses, Gross		$ 84,200,000
Real Estate Under Development, Completed [Member]
Real Estate Investment Property, Net		$ 38,000,000
Acquired Land [Member]
Number of Real Estate Properties		3		2
Payments to Acquire Real Estate		$ 13,800,000		$ 20,700,000

[1] Gross leasable area ("GLA")

[2] The Company utilized $66.0 million associated with Internal Revenue Code 1031 sales proceeds.

[3] The Company utilized $89.5 million associated with Internal Revenue Code 1031 sales proceeds.