Note 8 - Capital Stock - Dividends Declared (Details) - USD ($) $ / shares in Units, $ in Thousands			3 Months Ended		4 Months Ended		12 Months Ended											135 Months Ended
		Apr. 10, 2024	Mar. 31, 2024	Mar. 31, 2023	Apr. 26, 2024		Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Mar. 31, 2024
Cash dividends declared, per share (in dollars per share)			$ 0.36	$ 0.48			$ 1.8	$ 2.475	$ 3.9	$ 3.95	$ 4.8	$ 5.35	$ 8.4	$ 8.4	$ 9.6	$ 10.8	$ 6.975	$ 66.93
Dividends							$ 81,127	$ 87,906	$ 97,601	$ 53,570	$ 54,421	$ 55,814	$ 70,717	$ 41,388	$ 38,748	$ 22,643	$ 4,662	$ 633,686
Subsequent Event [Member]
Cash dividends declared, per share (in dollars per share)		$ 0.12			$ 0.48	[1]
Dividends	[1]				$ 25,089

[1] On April 10, 2024, the Company declared a dividend of $0.12 per share to be paid on May 30, 2024. The effect of this dividend is included in the table above but is not reflected in the Company’s financial statements as of March 31, 2024.