Note 8 - Capital Stock - Dividends Declared (Details) - USD ($) $ / shares in Units, $ in Thousands				2 Months Ended			12 Months Ended											132 Months Ended
		Feb. 14, 2024	Jan. 10, 2024	Feb. 27, 2024	Feb. 17, 2024	[1]	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	Dec. 31, 2023
Per share amount (in dollars per share)							$ 1.8	$ 2.475	$ 3.9	$ 3.95	$ 4.8	$ 5.35	$ 8.4	$ 8.4	$ 9.6	$ 10.8	$ 6.975	$ 66.69
Dividends							$ 81,127	$ 87,906	$ 97,601	$ 53,570	$ 54,421	$ 55,814	$ 70,717	$ 41,388	$ 38,748	$ 22,643	$ 4,662	$ 620,959
Subsequent Event [Member]
Per share amount (in dollars per share)		$ 0.12	$ 0.12		$ 0.24
Dividends	[1]			$ 12,362

[1] On January 10, 2024, the Company declared a dividend of $0.12 per share to be paid on February 27, 2024. On February 14, 2024, the Company declared a dividend of $0.12 per share to be paid on March 29, 2024. The effect of these dividends are included in the table above, but are not reflected in the Company’s financial statements as of December 31, 2023.