Note 7 - Capital Stock (Details Textual) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended				12 Months Ended										92 Months Ended	123 Months Ended
	Apr. 12, 2023	Apr. 12, 2023	[1]	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	Mar. 31, 2023	Apr. 28, 2023	Oct. 12, 2022	Aug. 30, 2022	Dec. 09, 2021	Feb. 08, 2018	Feb. 01, 2018	Jul. 29, 2015
Common Stock, Par or Stated Value Per Share (in dollars per share)				$ 0.01		$ 0.01										$ 0.01	$ 0.01			$ 0.01
Stock Repurchased and Retired During Period, Value				$ 3,963
Common Stock, Dividends, Per Share, Declared (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
Subsequent Event [Member]
Common Stock, Dividends, Per Share, Declared (in dollars per share)	$ 0.16	$ 0.640
Share Repurchase Program [Member]
Stock Repurchase Program, Number of Shares Authorized to be Repurchased (in shares)																								400,000
Stock Repurchase Program, Additional Shares Authorized (in shares)																			4,300,000		3,372,399		904,564
Stock Repurchase Program, Remaining Number of Shares Authorized to be Repurchased (in shares)																			6,183,601		3,539,861	1,061,316		156,751
Stock Repurchased and Retired During Period, Shares (in shares)				373,041		2,538,470										4,048,613
Stock Repurchased and Retired During Period, Value				$ 4,000		$ 24,500										$ 68,800
Shares Acquired, Average Cost Per Share (in dollars per share)				$ 10.62		$ 9.63										$ 16.99
Share Repurchase Program [Member] | Subsequent Event [Member]
Stock Repurchase Program, Remaining Number of Shares Authorized to be Repurchased (in shares)																		4,928,350

[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.