Note 8 - Capital Stock - Dividends Declared (Details) - USD ($)			2 Months Ended		3 Months Ended		12 Months Ended												147 Months Ended
		Apr. 09, 2025	May 29, 2025		Mar. 31, 2025	Mar. 31, 2024	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	Mar. 31, 2025
Common Stock, Dividends, Per Share, Declared (in dollars per share)					$ 0.36	$ 0.36	$ 1.44	$ 1.8	$ 2.475	$ 3.9	$ 3.95	$ 4.8	$ 5.35	$ 8.4	$ 8.4	$ 9.6	$ 10.8	$ 6.975	$ 68.37
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	$ 753,469,000
Subsequent Event [Member]
Common Stock, Dividends, Per Share, Declared (in dollars per share)		$ 0.12	$ 0.48	[1]
Dividends	[1]		$ 48,563,000

[1] On April 9, 2025, the Company declared a dividend of $0.12 per share to be paid on May 29, 2025. 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, 2025.