Note 12 - Fair Value Measurements (Details Textual) $ in Thousands		9 Months Ended
		Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Dec. 31, 2018 USD ($)
Impairment of Real Estate		$ 41,200	$ 33,900
Measurement Input, Cap Rate [Member] | Minimum [Member]
Real Estate, Measurement Input		0.0800
Measurement Input, Cap Rate [Member] | Maximum [Member]
Real Estate, Measurement Input		0.1100
Measurement Input, Discount Rate [Member] | Minimum [Member]
Real Estate, Measurement Input		0.0850
Measurement Input, Discount Rate [Member] | Maximum [Member]
Real Estate, Measurement Input		0.1250
Estimate of Fair Value Measurement [Member]
Notes Payable, Fair Value Disclosure	[1]	$ 5,000,047		$ 4,126,450
Fair Value, Inputs, Level 2 [Member] | Estimate of Fair Value Measurement [Member]
Notes Payable, Fair Value Disclosure		4,800,000		4,000,000
Fair Value, Inputs, Level 3 [Member] | Estimate of Fair Value Measurement [Member]
Notes Payable, Fair Value Disclosure		$ 199,800		$ 97,600

[1] The Company determined that the valuation of its Senior Unsecured Notes were classified within Level 2 of the fair value hierarchy and its unsecured revolving credit facility was classified within Level 3 of the fair value hierarchy. The estimated fair value amounts classified as Level 2, as of September 30, 2019 and December 31, 2018, were $4.8 billion and $4.0 billion, respectively. The estimated fair value amounts classified as Level 3, as of September 30, 2019 and December 31, 2018, were $199.8 million and $97.6 million, respectively.