Note 8 - Capital Stock - Dividends Declared (Details) - USD ($) $ / shares in Units, $ in Thousands			3 Months Ended		9 Months Ended				12 Months Ended										129 Months Ended
		Oct. 11, 2023	Sep. 30, 2023	Sep. 30, 2022	Oct. 11, 2023		Sep. 30, 2023	Sep. 30, 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	Sep. 30, 2023
Dividends declared per common share (in dollars per share)			$ 0.480	$ 0.545			$ 1.440	$ 1.995	$ 2.475	$ 3.900	$ 3.950	$ 4.800	$ 5.350	$ 8.400	$ 8.400	$ 9.600	$ 10.800	$ 6.975	$ 66.210
Dividends									$ 87,906	$ 97,601	$ 53,570	$ 54,421	$ 55,814	$ 70,717	$ 41,388	$ 38,748	$ 22,643	$ 4,662	$ 596,074
Subsequent Event [Member]
Dividends declared per common share (in dollars per share)		$ 0.12			$ 1.560	[1]
Dividends	[1]				$ 68,604

[1] On October 11, 2023, the Company declared a dividend of $0.12 per share to be paid on November 28, 2023. The effect of this dividend is included in the table above but is not reflected in the Company’s financial statements as of September 30, 2023.