Note 8 - Share-based Compensation - Stock Option Activity (Details) - $ / shares	6 Months Ended
Jun. 30, 2021	Jun. 30, 2020
Share-based Payment Arrangement, Option [Member]
Outstanding (in shares)	844,455
Outstanding, weighted average exercise price (in dollars per share)	$ 2.00
Exercised (in shares)	(100,269)
Exercised, weighted average exercise price (in dollars per share)	$ 1.36
Forfeited (in shares)	(1,146)
Forfeited, weighted average exercise price (in dollars per share)	$ 5.69
Expired (in shares)	(35,714)
Expired, weighted average exercise price (in dollars per share)	$ 1.73
Outstanding (in shares)	707,326
Outstanding as of June 30, 2021 (in dollars per share)	$ 2.09
Options exercisable (in shares)	703,787
Options exercisable, weighted average exercise price (in dollars per share)	$ 2.09
Performance Shares [Member]
Outstanding (in shares)		686,001
Outstanding, weighted average exercise price (in dollars per share)		$ 1.64
Exercised (in shares)		(287,490)
Exercised, weighted average exercise price (in dollars per share)		$ 1.64
Outstanding (in shares)		398,511
Outstanding as of June 30, 2021 (in dollars per share)		$ 1.64
Options exercisable (in shares)		398,511
Options exercisable, weighted average exercise price (in dollars per share)		$ 1.64

The number of shares into which fully or partially vested stock options outstanding as of the balance sheet date can be currently converted under the option plan.

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The weighted-average price as of the balance sheet date at which grantees can acquire the shares reserved for issuance on vested portions of options outstanding and currently exercisable under the stock option plan.

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Number of options outstanding, including both vested and non-vested options.

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Weighted average price at which grantees can acquire the shares reserved for issuance under the stock option plan.

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Weighted average price at which option holders acquired shares when converting their stock options into shares.

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Weighted average price at which grantees could have acquired the underlying shares with respect to stock options of the plan that expired.

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