Note 11 - Fair Value Measurements (Details Textual) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Asset Impairment Charges, Total		$ 397	$ 19,609	$ 3,509	$ 41,235
Estimate of Fair Value Measurement [Member]
Notes Payable, Fair Value Disclosure	[1]	5,298,739		5,298,739		$ 4,983,763
Fair Value, Inputs, Level 2 [Member] | Estimate of Fair Value Measurement [Member]
Notes Payable, Fair Value Disclosure		$ 5,300		$ 5,300		4,800,000
Fair Value, Inputs, Level 3 [Member] | Estimate of Fair Value Measurement [Member]
Notes Payable, Fair Value Disclosure						$ 199,900

[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, 2020 and December 31, 2019, were $5.3 billion and $4.8 billion, respectively. The estimated fair value amounts classified as Level 3, as of December 31, 2019, was $199.9 million.