Note 7 - Capital Stock - Dividends Declared (Details) - USD ($) $ / shares in Units, $ in Thousands			3 Months Ended				12 Months Ended										123 Months Ended
		Apr. 12, 2023	Apr. 12, 2023		Mar. 31, 2023	Mar. 31, 2022	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, 2023
Dividends declared per common share (in dollars per share)					$ 0.480	$ 0.775	$ 2.475	$ 3.900	$ 3.950	$ 4.800	$ 5.350	$ 8.400	$ 8.400	$ 9.600	$ 10.800	$ 6.975	$ 65.290
Dividends							$ 87,906	$ 97,601	$ 53,570	$ 54,421	$ 55,814	$ 70,717	$ 41,388	$ 38,748	$ 22,643	$ 4,662	$ 552,568
Subsequent Event [Member]
Dividends declared per common share (in dollars per share)		$ 0.16	$ 0.640	[1]
Dividends	[1]		$ 25,098

[1] On April 12, 2023, the Company declared a dividend of $0.16 per share to be paid on May 26, 2023. 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, 2023.