Note 6 - Stockholders' Equity (Details Textual) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended			6 Months Ended
	May 05, 2022	Jun. 30, 2022	Mar. 31, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Share-Based Payment Arrangement, Expense		$ 1,300		$ 2,800	$ 2,500	$ 3,300
Share-Based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount, Total		$ 9,100			$ 9,100
Share-Based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition (Year)					2 years 4 months 24 days
Share-Based Payment Arrangement, Shares Withheld for Tax Withholding Obligation (in shares)					737,258	574,251
Share-Based Payment Arrangement, Decrease for Tax Withholding Obligation					$ 3,700	$ 4,500
Shares Withheld for Tax Withholding Obligation, Price Per Share (in dollars per share)		$ 4.99		$ 7.88	$ 4.99	$ 7.88
Common Stock, Dividends, Per Share, Declared (in dollars per share)		$ 0.00625		$ 0.01	$ 0.01225	$ 0.02
Dividends, Common Stock, Total		$ 3,380		$ 6,027	$ 6,751	$ 10,715
Average Realized Silver Price Per Ounce (in dollars per share)			$ 24.68
Quarterly Dividends [Member]
Common Stock, Dividends, Per Share, Declared (in dollars per share)	$ 0.00625
Quarterly Dividends, Common Stock, Cash, Minimum Dividend Component (in dollars per share)	0.00375
Quarterly Dividends, Common Stock, Cash, Silver Price-linked Component (in dollars per share)	$ 0.0025
Dividends, Common Stock, Total		$ 3,400
Dividends Payable, Date Declared	May 05, 2022