Note 7 - Capital Stock - Dividends Declared (Details) - USD ($) $ / shares in Units, $ in Thousands				2 Months Ended		12 Months Ended										110 Months Ended
		Feb. 15, 2023	Jan. 11, 2023	Feb. 24, 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	Feb. 24, 2023
Per share amount (in dollars per share)						$ 2.475	$ 3.900	$ 3.950	$ 4.800	$ 5.350	$ 8.400	$ 8.400	$ 9.600	$ 10.800	$ 6.975	$ 64.970
Dividends						$ 87,906	$ 97,601	$ 53,570	$ 54,421	$ 55,814	$ 70,717	$ 41,388	$ 38,748	$ 22,643	$ 4,662	$ 540,010
Subsequent Event [Member]
Per share amount (in dollars per share)		$ 0.16	$ 0.16	$ 0.320	[1]
Dividends	[1]			$ 12,540

[1] On January 11, 2023, the Company declared a dividend of $0.16 per share that was paid on February 24, 2023. On February 15, 2023, the Company declared a dividend of $0.16 per share to be paid on March 29, 2023. 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, 2022.