Note 6 - Stockholders' Equity - Schedule of Accumulated other comprehensive income (loss) (Details) - USD ($) $ in Thousands	3 Months Ended
	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022
Balance Begning	$ 1,992,836		$ 1,978,967	$ 1,782,882		$ 1,760,787
Balance Ending	1,977,770	$ 1,992,836		1,954,768	$ 1,782,882
Changes in fair value of derivative contracts designated as hedge transactions [Member]
Balance Begning	20,910	15,678	9,162	27,508	(37,840)	(4,675)
Changes in fair value of derivative contracts	(5,265)	7,445	8,665	(16,701)	61,939	(31,798)
Gains and deferred gains transferred from accumulated other comprehensive income	(6,119)	(2,213)	(2,149)	4,009	3,409	(1,367)
Balance Ending	9,526	20,910	15,678	14,816	27,508	(37,840)
Adjustments For Pension Plans [Member]
Balance Begning	(6,714)	(6,714)	(6,714)	(23,781)	(23,781)	(23,781)
Changes in fair value of derivative contracts	0	0	0	0	0	0
Gains and deferred gains transferred from accumulated other comprehensive income	0	0	0	0	0	0
Balance Ending	(6,714)	(6,714)	(6,714)	(23,781)	(23,781)	(23,781)
Accumulated Distributions in Excess of Net Income [Member]
Balance Begning	14,196	8,964	2,448	3,727	(61,621)	(28,456)
Changes in fair value of derivative contracts	(5,265)	7,445	8,665	(16,701)	61,939	(31,798)
Gains and deferred gains transferred from accumulated other comprehensive income	(6,119)	(2,213)	(2,149)	4,009	3,409	(1,367)
Balance Ending	$ 2,812	$ 14,196	$ 8,964	$ (8,965)	$ 3,727	$ (61,621)