Note 11 - Common Stock and Stock-based Compensation Plans (Details Textual) - USD ($) | Feb. 18, 2021 | Feb. 16, 2021 | Feb. 15, 2021 | Feb. 20, 2020 | Jun. 30, 2021 | Jun. 30, 2020 | Jun. 30, 2021 | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2020 |
Share-based Compensation Arrangement by Share-based Payment Award, Options and Stock Appreciation Rights, Outstanding Number (in shares) | [2] | | | | | 135,774 | [1] | | 135,774 | [1] | | | 289,069 |
Share-based Compensation Arrangement by Share-based Payment Award, Options and Stock Appreciation Rights, Exercisable Number (in shares) | [2],[3] | | | | | 135,774 | | | 135,774 | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Options and Stock Appreciation Rights, Grants in Period (in shares) | [2] | | | | | | | | 0 | | | | |
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount, Total | | | | | | $ 19,313,000 | | | $ 19,313,000 | | | | |
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition (Year) | | | | | | | | | 1 year 7 months 6 days | | | | |
Non-employee Director [Member] | | | | | | | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Annual Vesting, Percentage | | | | | | 25.00% | | | 25.00% | | | | |
The2011 Stock Incentive Plan [Member] | | | | | | | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Options and Stock Appreciation Rights Vesting Percentage, Year One | | | | | | 25.00% | | | 25.00% | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Remaining Vesting Period (Month) | | | | | | | | | 36 months | | | | |
Maximum [Member] | | | | | | | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Options and Stock Appreciation Rights, Outstanding Number (in shares) | | | | | | 131,581 | | | 131,581 | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Options and Stock Appreciation Rights, Exercisable Number (in shares) | | | | | | 131,581 | | | 131,581 | | | | |
Maximum [Member] | The2011 Stock Incentive Plan [Member] | | | | | | | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period (Year) | | | | | | | | | 4 years | | | | |
Stock Appreciation Rights (SARs) [Member] | Maximum [Member] | | | | | | | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Percentage of Awards Granted | | | | | | 400.00% | | | 400.00% | | | | |
Percentage of Stock Appreciation Rights Units Subject to Grant | | | | | | | | | 75.00% | | | | |
Restricted Stock Units (RSUs) [Member] | Vesting on February 18, 2022 [Member] | | | | | | | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage | | 33.40% | | | | | | | | | | | |
Restricted Stock Units (RSUs) [Member] | Vesting on February 18, 2023 [Member] | | | | | | | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage | | 33.30% | | | | | | | | | | | |
Restricted Stock Units (RSUs) [Member] | Vesting on February 18, 2024 [Member] | | | | | | | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage | | 33.30% | | | | | | | | | | | |
Restricted Stock Units (RSUs) [Member] | Non-employee Director [Member] | | | | | | | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period (Year) | | | | | | | | | | | 2 years | 1 year | |
Share-based Compensation Arrangement by Share-based Payment Award, Accelerated Vesting, Number (in shares) | | | | 5,902 | | | | | | | | | |
Restricted Stock Units (RSUs) [Member] | Employees [Member] | | | | | | | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period (Year) | | | | | | | | | 3 years | | | | |
Restricted Stock Units (RSUs) [Member] | The2011 Stock Incentive Plan [Member] | Non-employee Director [Member] | | | | | | | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period (Year) | | | 2 years | | | | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period (in shares) | | | 1,784 | | | | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Fair Value | | | $ 124,670 | | | | | | | | | | |
Restricted Stock Units (RSUs) [Member] | The2011 Stock Incentive Plan [Member] | Non-employee Director [Member] | Vesting After the First Anniversary Grant Date [Member] | | | | | | | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage | | | 50.00% | | | | | | | | | | |
Restricted Stock Units (RSUs) [Member] | The2011 Stock Incentive Plan [Member] | Chief Executive Officer [Member] | | | | | | | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period (in shares) | | 5,962 | | | | | | | | | | | |
Restricted Stock Units (RSUs) [Member] | The2011 Stock Incentive Plan [Member] | Executive Vice President, Worldwide Sales [Member] | | | | | | | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period (in shares) | | 4,024 | | | | | | | | | | | |
Restricted Stock Units (RSUs) [Member] | The2011 Stock Incentive Plan [Member] | Chief Financial Officer [Member] | | | | | | | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period (in shares) | | 3,577 | | | | | | | | | | | |
Restricted Stock Units (RSUs) [Member] | The2011 Stock Incentive Plan [Member] | Chief Operating Officer [Member] | | | | | | | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period (in shares) | | 3,577 | | | | | | | | | | | |
Performance Share Units [Member] | The2011 Stock Incentive Plan [Member] | Chief Executive Officer [Member] | | | | | | | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period (in shares) | | 8,943 | | | | | | | | | | | |
Performance Share Units [Member] | The2011 Stock Incentive Plan [Member] | Executive Vice President, Worldwide Sales [Member] | | | | | | | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period (in shares) | | 2,683 | | | | | | | | | | | |
Performance Share Units [Member] | The2011 Stock Incentive Plan [Member] | Chief Financial Officer [Member] | | | | | | | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period (in shares) | | 2,385 | | | | | | | | | | | |
Performance Share Units [Member] | The2011 Stock Incentive Plan [Member] | Chief Operating Officer [Member] | | | | | | | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period (in shares) | | 2,385 | | | | | | | | | | | |
Short-Term Executive PSUs [Member] | | | | | | | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Addtional Shares Issuable, Performance Goals Exceeded, Percentage | | | | | 20.00% | | | | | | | | |
Short-Term Executive PSUs [Member] | Goals One [Member] | | | | | | | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage | | 50.00% | | | | | | | | | | | |
Short-Term Executive PSUs [Member] | Goals Two [Member] | | | | | | | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage | | 50.00% | | | | | | | | | | | |
Short-Term Executive PSUs [Member] | Vesting on February 20, 2021 [Member] | | | | | | | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage | | | | | | | | | 33.40% | | | | |
Short-Term Executive PSUs [Member] | Vesting on February 22, 2022 [Member] | | | | | | | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage | | | | | | | | | 33.30% | | | | |
Short-Term Executive PSUs [Member] | Vesting on February 20, 2023 [Member] | | | | | | | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage | | | | | | | | | 33.30% | | | | |
Short-Term Executive PSUs [Member] | Chief Executive Officer [Member] | | | | | | | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Addtional Shares Issuable, Performance Goals Exceeded (in shares) | | | | | 1,788 | | | | | | | | |
Short-Term Executive PSUs [Member] | Executive Vice President, Worldwide Sales [Member] | | | | | | | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Addtional Shares Issuable, Performance Goals Exceeded (in shares) | | | | | 536 | | | | | | | | |
Short-Term Executive PSUs [Member] | Chief Financial Officer [Member] | | | | | | | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Addtional Shares Issuable, Performance Goals Exceeded (in shares) | | | | | 477 | | | | | | | | |
Short-Term Executive PSUs [Member] | Chief Operating Officer [Member] | | | | | | | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Addtional Shares Issuable, Performance Goals Exceeded (in shares) | | | | | 477 | | | | | | | | |
Purchase Rights [Member] | The 2002 Employee Stock Purchase Plan [Member] | | | | | | | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period (in shares) | | | | | | 0 | | 0 | | | | | |
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[1] | Due to the ceiling imposed on the SAR grants, the outstanding amount equals a maximum of 131,581 shares of the Company’s common stock issuable upon exercise. | |
[2] | The SAR units are convertible for a maximum number of shares of the Company's common stock equal to 75% of the SAR units subject to the grant. | |
[3] | Due to the ceiling imposed on the SAR grants, the exercisable amount equals a maximum of 131,581 shares of the Company’s common stock issuable upon exercise. | |