Note 8 - Capital Stock - Dividends Declared (Details) - USD ($)				2 Months Ended		12 Months Ended												144 Months Ended
		Feb. 12, 2025	Jan. 08, 2025	Feb. 27, 2025		Dec. 31, 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	Dec. 31, 2024
Common Stock, Dividends, Per Share, Declared (in dollars per share)						$ 1.44	$ 1.8	$ 2.475	$ 3.9	$ 3.95	$ 4.8	$ 5.35	$ 8.4	$ 8.4	$ 9.6	$ 10.8	$ 6.975	$ 68.13
Dividends						$ 96,309	$ 81,127,000	$ 87,906,000	$ 97,601,000	$ 53,570,000	$ 54,421,000	$ 55,814,000	$ 70,717,000	$ 41,388,000	$ 38,748,000	$ 22,643,000	$ 4,662,000	$ 727,003,000
Subsequent Event [Member]
Common Stock, Dividends, Per Share, Declared (in dollars per share)		$ 0.12	$ 0.12	$ 0.24	[1]
Dividends	[1]			$ 22,097,000

[1] On January 8, 2025, the Company declared a dividend of $0.12 per share to be paid on February 27, 2025. On February 12, 2025, the Company declared a dividend of $0.12 per share to be paid on March 28, 2025. 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, 2024.