Note 7 - Capital Stock (Details Textual) - USD ($) $ / shares in Units, $ in Thousands			2 Months Ended		12 Months Ended										89 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	Dec. 31, 2022	Feb. 24, 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
Stock Repurchased and Retired During Period, Value					$ 24,610		$ 68
Common Stock, Dividends, Per Share, Declared (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
Subsequent Event [Member]
Common Stock, Dividends, Per Share, Declared (in dollars per share)	$ 0.16	$ 0.16	$ 0.320	[1]
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)					2,538,470	0									3,675,572
Stock Repurchased and Retired During Period, Value					$ 24,500										$ 64,800
Treasury Stock Acquired, Average Cost Per Share (in dollars per share)					$ 9.63										$ 17.63
Share Repurchase Program [Member] | Subsequent Event [Member]
Stock Repurchase Program, Remaining Number of Shares Authorized to be Repurchased (in shares)			4,928,350													4,928,350
Stock Repurchased and Retired During Period, Shares (in shares)			373,041
Stock Repurchased and Retired During Period, Value			$ 4,000
Treasury Stock Acquired, Average Cost Per Share (in dollars per share)			$ 10.62

[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.