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Note 11 - Stock-based Compensation (Tables) | 12 Months Ended
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Dec. 31, 2020
Notes Tables |
Share-based Payment Arrangement, Restricted Stock Unit, Activity [Table Text Block] |
|  | 2020 |  |  | 2019 |  |  | 2018 |
|  | Shares |  |  | Weighted Average Fair Value |  |  | Shares |  |  | Weighted Average Fair Value |  |  | Shares |  |  | Weighted Average Fair Value |
Nonvested at beginning of year |  |  | 262,260 |  |  | $ | 34.91 |  |  |  | 262,967 |  |  | $ | 33.97 |  |  |  | 239,637 |  |  | $ | 32.37 |
Granted |  |  | 121,518 |  |  |  | 24.65 |  |  |  | 84,596 |  |  |  | 35.29 |  |  |  | 91,400 |  |  |  | 31.82 |
Vested |  |  | (85,445 | ) |  |  | 37.08 |  |  |  | (81,772 | ) |  |  | 32.19 |  |  |  | (55,792 | ) |  |  | 25.14 |
Forfeited |  |  | (35,997 | ) |  |  | 33.71 |  |  |  | (3,531 | ) |  |  | 34.85 |  |  |  | (12,278 | ) |  |  | 31.62 |
Nonvested at end of year |  |  | 262,336 |  |  | $ | 29.42 |  |  |  | 262,260 |  |  | $ | 34.91 |  |  |  | 262,967 |  |  | $ | 33.97 |
Share-based Payment Arrangement, Option, Activity [Table Text Block] |
|  | 2020 |  |  | 2019 |  |  | 2018 |
|  | Shares |  |  | Weighted Average Exercise Price |  |  | Shares |  |  | Weighted Average Exercise Price |  |  | Shares |  |  | Weighted Average Exercise Price |
Outstanding at beginning of year |  |  | 10,700 |  |  | $ | 30.25 |  |  |  | 18,900 |  |  | $ | 23.92 |  |  |  | 30,908 |  |  | $ | 18.67 |
Granted |  |  | 0 |  |  | NA |  |  |  | 0 |  |  | NA |  |  |  | 0 |  |  | NA |
Exercised |  |  | (1,000 | ) |  |  | 5.19 |  |  |  | (8,200 | ) |  |  | 15.69 |  |  |  | (12,008 | ) |  |  | 10.38 |
Forfeited or expired |  |  | 0 |  |  | NA |  |  |  | 0 |  |  | NA |  |  |  | 0 |  |  | NA |
Outstanding at end of year |  |  | 9,700 |  |  | $ | 32.83 |  |  |  | 10,700 |  |  | $ | 30.25 |  |  |  | 18,900 |  |  | $ | 23.92 |
Options exercisable at year-end |  |  | 9,700 |  |  | $ | 32.83 |  |  |  | 10,700 |  |  | $ | 30.25 |  |  |  | 18,900 |  |  | $ | 23.92 |
Share-based Payment Arrangement, Option, Exercise Price Range [Table Text Block] |
|  |  |  | Outstanding |  |  | Exercisable |
|  |  |  |  |  |  |  | Weighted Average |  |  | Weighted |  |  |  |  |  |  | Weighted |
Range of |  |  |  |  |  |  |  | Remaining |  |  | Average |  |  |  |  |  |  | Average |
Exercise |  |  |  |  |  |  |  | Contractual |  |  | Exercise |  |  |  |  |  |  | Exercise |
Prices |  |  |  | Number |  |  | Life (Years) |  |  | Price |  |  | Number |  |  | Price |
$22.00 | - | $23.00 |  |  | 1,000 |  |  |  | 0.9 |  |  | $ | 22.15 |  |  |  | 1,000 |  |  |  | 22.15 |
$27.00 | - | $28.00 |  |  | 2,200 |  |  |  | 1.9 |  |  |  | 27.66 |  |  |  | 2,200 |  |  |  | 27.66 |
$36.00 | - | $37.00 |  |  | 6,500 |  |  |  | 2.9 |  |  |  | 36.22 |  |  |  | 6,500 |  |  |  | 36.22 |
Outstanding at year end |  |  | 9,700 |  |  |  | 2.4 |  |  | $ | 32.83 |  |  |  | 9,700 |  |  |  | 32.83 |
Schedule of Share-based Compensation Shares Authorized Under Stock Option Plans Information Related to Option Outstanding [Table Text Block] |
|  | 2020 |  |  | 2019 |  |  | 2018 |
Minimum exercise price |  | $ | 22.15 |  |  | $ | 5.19 |  |  | $ | 5.19 |
Maximum exercise price |  |  | 36.22 |  |  |  | 36.22 |  |  |  | 36.22 |
Average remaining option term (years) |  |  | 2.4 |  |  |  | 3.2 |  |  |  | 3.4 |
Schedule of Share Based Compensation Arrangement by Share Based Payment Award Options Information Related to Stock Option Grants and Exercised [Table Text Block] |
|  | 2020 |  |  | 2019 |  |  | 2018 |
Aggregate intrinsic value of stock options exercised |  | $ | 17,000 |  |  | $ | 157,000 |  |  | $ | 317,000 |
Cash received from stock option exercises |  |  | 3,000 |  |  |  | 126,000 |  |  |  | 141,000 |
Tax benefit realized from stock option exercises |  |  | 0 |  |  |  | 0 |  |  |  | 0 |
Weighted average per share fair value of stock options granted |  |  | NA |  |  |  | NA |  |  | NA |

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