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Note 13 - Stock-based Compensation (Tables) | 12 Months Ended
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Dec. 31, 2021
Notes Tables |
Share-based Payment Arrangement, Cost by Plan [Table Text Block] |
|  | Year Ended December 31, |
(in thousands) |  | 2021 |  |  | 2020 |  |  | 2019 |
Stock options and other |  | $ | 17,553 |  |  | $ | 13,327 |  |  | $ | 9,591 |
Employee stock purchase plan |  |  | 1,542 |  |  |  | 1,346 |  |  |  | 1,190 |
Total stock-based compensation expense |  | $ | 19,095 |  |  | $ | 14,673 |  |  | $ | 10,781 |
Cost of revenue |  | $ | 2,595 |  |  | $ | 2,451 |  |  | $ | 2,056 |
Operating expenses: |  |  |  |  |  |  |  |  |  |  |  |
Marketing and sales |  |  | 3,736 |  |  |  | 3,121 |  |  |  | 2,632 |
Research and development |  |  | 2,833 |  |  |  | 2,440 |  |  |  | 1,851 |
General and administrative |  |  | 9,931 |  |  |  | 6,661 |  |  |  | 4,242 |
Total stock-based compensation expense |  | $ | 19,095 |  |  | $ | 14,673 |  |  | $ | 10,781 |
Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions [Table Text Block] |
|  | Year Ended December 31, |
|  | 2021 |  |  | 2020 |  |  | 2019 |
Risk-free interest rate |  |  | 0.80 - 1.12% |  |  |  | 0.50 - 1.47% |  |  |  | 2.35 - 2.58% |
Expected life (years) |  |  | 6.25 |  |  |  | 6.25 |  |  |  | 6.25 |
Expected volatility |  |  | 45.28 - 45.53% |  |  |  | 42.40 - 43.83% |  |  |  | 42.52 - 42.74% |
Expected dividend yield |  |  | 0% |  |  |  | 0% |  |  |  | 0% |
Weighted average grant date fair value |  |  | $128.14 |  |  |  | $45.32 |  |  |  | $47.84 |
Share-based Payment Arrangement, Option, Activity [Table Text Block] |
|  |  |  |  |  | Weighted- |
|  |  |  |  |  | Average |
|  | Stock Options |  |  | Exercise Price |
Options outstanding at January 1, 2019 |  |  | 252,616 |  |  | $ | 64.71 |
Granted |  |  | 53,708 |  |  |  | 105.81 |
Exercised |  |  | (16,079 | ) |  |  | 48.67 |
Cancelled |  |  | (13,979 | ) |  |  | 89.50 |
Options outstanding at December 31, 2019 |  |  | 276,266 |  |  |  | 72.38 |
Granted |  |  | 60,065 |  |  |  | 105.79 |
Exercised |  |  | (68,958 | ) |  |  | 57.00 |
Cancelled |  |  | (37,842 | ) |  |  | 67.92 |
Options outstanding at December 31, 2020 |  |  | 229,531 |  |  |  | 86.46 |
Granted |  |  | 57,901 |  |  |  | 128.14 |
Exercised |  |  | (28,991 | ) |  |  | 58.78 |
Cancelled |  |  | (25,057 | ) |  |  | 109.31 |
Options outstanding at December 31, 2021 |  |  | 233,384 |  |  | $ | 97.78 |
Exercisable at December 31, 2021 |  |  | 115,700 |  |  | $ | 81.30 |
Share-based Payment Arrangement, Option, Exercise Price Range [Table Text Block] |
|  | Options Outstanding, Vested and Expected to Vest |  |  | Options Exercisable |
Range of Exercise Prices |  | Number Outstanding |  |  | Weighted Average Remaining Contractual Life |  |  | Weighted Average Exercise Price ($) |  |  | Number Exercisable |  |  | Weighted Average Exercise Price ($) |
$7.76 to $31.43 |  | 4,624 |  |  | 0.35 |  |  | 30.58 |  |  | 4,624 |  |  | 30.58 |
$31.44 to $66.87 |  | 50,159 |  |  | 3.58 |  |  | 57.13 |  |  | 45,986 |  |  | 57.02 |
$66.88 to $96.20 |  | 41,586 |  |  | 7.82 |  |  | 89.95 |  |  | 9,570 |  |  | 71.68 |
$96.21 to $180.46 |  | 137,015 |  |  | 7.67 |  |  | 117.31 |  |  | 55,520 |  |  | 107.28 |
Share-based Payment Arrangement, Restricted Stock and Restricted Stock Unit, Activity [Table Text Block] |
|  |  |  |  |  | Weighted- |
|  |  |  |  |  | Average |
|  |  |  |  |  | Grant Date |
|  | Restricted |  |  | Fair Value |
|  | Stock Awards |  |  | Per Share |
Restricted stock at January 1, 2019 |  |  | 323,921 |  |  | $ | 79.85 |
Granted |  |  | 115,471 |  |  |  | 106.35 |
Restrictions lapsed |  |  | (92,597 | ) |  |  | 77.25 |
Forfeited |  |  | (31,822 | ) |  |  | 87.58 |
Restricted stock at December 31, 2019 |  |  | 314,973 |  |  |  | 89.55 |
Granted |  |  | 108,179 |  |  |  | 111.76 |
Restrictions lapsed |  |  | (101,941 | ) |  |  | 84.70 |
Forfeited |  |  | (14,012 | ) |  |  | 94.24 |
Restricted stock at December 31, 2020 |  |  | 307,199 |  |  |  | 98.87 |
Granted |  |  | 205,996 |  |  |  | 123.61 |
Restrictions lapsed |  |  | (115,908 | ) |  |  | 91.26 |
Forfeited |  |  | (53,505 | ) |  |  | 128.05 |
Restricted stock at December 31, 2021 |  |  | 343,782 |  |  | $ | 111.79 |
Schedule of Nonvested Performance-based Units Activity [Table Text Block] |
|  |  |  |  |  | Weighted- |
|  |  |  |  |  | Average |
|  |  |  |  |  | Grant Date |
|  | Performance |  |  | Fair Value |
|  | Stock Awards |  |  | Per Share |
Performance stock at January 1, 2019 |  |  | 52,140 |  |  | $ | 76.54 |
Granted |  |  | 21,434 |  |  |  | 104.99 |
Restrictions lapsed |  |  | - |  |  |  | - |
Performance change |  |  | (61,816 | ) |  |  | 88.06 |
Forfeited |  |  | (2,375 | ) |  |  | 105.37 |
Performance stock at December 31, 2019 |  |  | 9,383 |  |  |  | 58.35 |
Granted |  |  | 19,956 |  |  |  | 118.66 |
Restrictions lapsed |  |  | (7,113 | ) |  |  | 58.35 |
Performance change |  |  | - |  |  |  | - |
Forfeited |  |  | (2,270 | ) |  |  | 58.35 |
Performance stock at December 31, 2020 |  |  | 19,956 |  |  |  | 118.66 |
Granted |  |  | 15,078 |  |  |  | 203.64 |
Restrictions lapsed |  |  | - |  |  |  | - |
Performance change |  |  | (10,366 | ) |  |  | 192.95 |
Forfeited |  |  | (7,829 | ) |  |  | 113.91 |
Performance stock at December 31, 2021 |  |  | 16,839 |  |  | $ | 115.56 |
Schedule of Share-based Payment Award, Awards Other Than Stock Options, Valuation Assumptions [Table Text Block] |
|  | Year Ended December 31, |
|  | 2021 |  |  | 2020 |  |  | 2019 |
Risk-free interest rate |  | 0.06 - 0.17% |  |  | 0.12 - 0.17% |  |  | 1.59 - 2.35% |
Expected life (months) |  | 6.00 |  |  | 6.00 |  |  | 6.00 |
Expected volatility |  | 53.44 - 65.53% |  |  | 50.85 - 59.99% |  |  | 42.63 - 53.57% |
Expected dividend yield |  | 0% |  |  | 0% |  |  | 0% |

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