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Note 8 - Shareholders' Equity (Details Textual) $ / shares in Units, $ in Millions		1 Months Ended		3 Months Ended		6 Months Ended		28 Months Ended	74 Months Ended
	Aug. 08, 2018 USD ($) $ / shares	Jun. 30, 2018 USD ($) $ / item shares	Mar. 31, 2018 USD ($) shares	Jun. 30, 2018 USD ($) $ / shares $ / item shares	Jun. 30, 2017 $ / shares	Jun. 30, 2018 USD ($) $ / shares $ / item shares	Jun. 30, 2017 USD ($) $ / shares shares	Jun. 30, 2018 USD ($) $ / item shares	Jun. 30, 2018 USD ($) $ / shares $ / item shares	Aug. 07, 2018 $ / shares	Feb. 23, 2016 USD ($)	May 08, 2012 shares
Share-based Compensation Arrangement by Share-based Payment Award, Shares Issued in Period \| shares			1,237,369
Allocated Share-based Compensation Expense, Total			$ 4.9
Share-based Compensation Arrangement by Share-based Payment Award, Measurement Period Used to Value Performance-based Awards		3 years
Shares Paid for Tax Withholding for Share Based Compensation \| shares						697,341	488,634
Payments Related to Tax Withholding for Share-based Compensation						$ 2.7	$ 2.5
Treasury Stock Acquired, Average Cost Per Share \| $ / shares						$ 3.86	$ 5.06
Common Stock, Dividends, Per Share, Declared \| $ / shares				$ 0.0025	$ 0.0025	$ 0.005	$ 0.005
Average Realized Silver Price \| $ / item						16.61
Average Realized Silver Price, Minimum Dividend, Threshold \| $ / item		30		30		30		30	30
Stock Issued During Period, Shares, New Issues \| shares						0		4,608,847
Stock Issued During Period, Value, New Issues								$ 17.7
Payments for Brokerage Fees								$ 0.4
Common Stock Repurchase Program [Member]
Treasury Stock Acquired, Average Cost Per Share \| $ / shares									$ 3.99
Stock Repurchase Program, Number of Shares Authorized to be Repurchased \| shares												20,000,000
Cumulative Stock Repurchased \| shares		934,100		934,100		934,100		934,100	934,100
Stock Repurchase Program, Remaining Number of Shares Authorized to be Repurchased \| shares		19,100,000		19,100,000		19,100,000		19,100,000	19,100,000
Subsequent Event [Member]
Common Stock, Dividends, Per Share, Declared \| $ / shares	$ 0.0025
Dividends, Common Stock, Total	$ 1.0
Subsequent Event [Member] \| Common Stock Repurchase Program [Member]
Share Price \| $ / shares										$ 2.92
Minimum [Member]
Common Stock, Dividends, Per Share, Declared \| $ / shares						$ 0.01
Maximum [Member]
Common Stock, Aggregate Offering Price											$ 75.0
Restricted Stock Units (RSUs) [Member]
Allocated Share-based Compensation Expense, Total		$ 5.6
Restricted Stock Units RSUs, Vesting In June 2019, June 2020, and June 2021 [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period \| shares		1,322,461
Restricted Stock Units RSUs, Vesting In June 2019, June 2020, and June 2021 [Member] \| Share-based Compensation Award, Tranche One [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage		33.00%
Restricted Stock Units RSUs, Vesting In June 2019, June 2020, and June 2021 [Member] \| Share-based Compensation Award, Tranche Two [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage		33.00%
Restricted Stock Units RSUs, Vesting In June 2019, June 2020, and June 2021 [Member] \| Share-based Compensation Award, Tranche Three [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage		33.00%
Restricted Stock Units RSUs, Vesting in June 2019 and June 2020 [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period \| shares		96,604
Restricted Stock Units RSUs, Vesting in June 2019 and June 2020 [Member] \| Share-based Compensation Award, Tranche One [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage		50.00%
Restricted Stock Units RSUs, Vesting in June 2019 and June 2020 [Member] \| Share-based Compensation Award, Tranche Two [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage		50.00%
Restricted Stock Units RSUs, Vesting in June 2019 [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period \| shares		28,721
Employee Service Share-based Compensation, Nonvested Awards, Compensation Not yet Recognized, Share-based Awards Other than Options		$ 2.0		$ 2.0		$ 2.0		$ 2.0	$ 2.0
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition		1 year
Restricted Stock Units (RSUs) Vesting in June 2020 [Member]
Employee Service Share-based Compensation, Nonvested Awards, Compensation Not yet Recognized, Share-based Awards Other than Options		$ 1.9		1.9		1.9		1.9	1.9
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition		2 years
Restricted Stock Units (RSUs) Vesting in June 2021 [Member]
Employee Service Share-based Compensation, Nonvested Awards, Compensation Not yet Recognized, Share-based Awards Other than Options		$ 1.7		$ 1.7		1.7		$ 1.7	$ 1.7
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition		3 years
Performance Shares [Member]
Allocated Share-based Compensation Expense, Total						$ 2.4	$ 2.8
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition		30 years