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Note 3 - Stock-based Compensation - Stock Option Activity (Details)
6 Months Ended
Jun. 30, 2018
$ / shares
shares
Outstanding (in shares) | shares 19,750
Outstanding, weighted average exercise price (in dollars per share) | $ / shares $ 20.94
Exercised (in shares) | shares (6,000)
Exercised, weighted average exercise price (in dollars per share) | $ / shares $ 23
Outstanding (in shares) | shares 13,750
Outstanding, weighted average exercise price (in dollars per share) | $ / shares $ 20.05
Exercisable (in shares) | shares 13,750
Exercisable, weighted average exercise price (in dollars per share) | $ / shares $ 20.05