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Stock Options (Details) - USD ($) | 3 Months Ended | 9 Months Ended |
--- | --- | --- | ---
Sep. 30, 2018 | Sep. 30, 2017 | Sep. 30, 2018 | Sep. 30, 2017 | Apr. 05, 2012
Stock options under 2012 Plan |  |  |  |  |
Stock option details |  |  |  |  |
Shares available for future grants | 7,625 |  | 7,625 |  | 800,000
Maximum exercisable period for options granted |  |  | 10 years |  |
Stock option activity |  |  |  |  |
Options outstanding at the beginning of the period (in shares) |  |  | 668,166 |  |
Plus: Options granted (in shares) |  |  | 229,700 |  |
Less: |  |  |  |  |
Options exercised (in shares) |  |  | 64,026 |  |
Options forfeited (in shares) |  |  | 21,113 |  |
Options outstanding at the end of the period (in shares) | 812,727 |  | 812,727 |  |
Options fully vested and exercisable at the end of the period (in shares) | 322,360 |  | 322,360 |  |
Stock Options, Weighted average exercise price |  |  |  |  |
Options outstanding at the beginning, weighted average exercise price (in dollars per share) |  |  | $ 20.41 |  |
Plus: Options granted, weighted average exercise price (in dollars per share) |  |  | 38.30 |  |
Less: |  |  |  |  |
Options exercised, weighted average exercise price (in dollars per share) |  |  | 18.00 |  |
Options forfeited, weighted average exercise price (in dollars per share) |  |  | 20.83 |  |
Options outstanding at the end, weighted average exercise price (in dollars per share) | $ 25.65 |  | 25.65 |  |
Options fully vested and exercisable at the end, weighted average exercise price (in dollars per share) | $ 19.77 |  | $ 19.77 |  |
Stock Options, Weighted average remaining contractual term (years) |  |  |  |  |
Options outstanding at the end, weighted average remaining contractual term (years) |  |  | 6 years 2 months 19 days |  |
Options fully vested and exercisable at the end, weighted average remaining contractual term (years) |  |  | 4 years 4 months 13 days |  |
Stock Options, Aggregate intrinsic value |  |  |  |  |
Options outstanding at the end, aggregate intrinsic value | $ 15,728,000 |  | $ 15,728,000 |  |
Options fully vested and exercisable at the end, aggregate intrinsic value | 8,135,000 |  | 8,135,000 |  |
Stock-based compensation expense | 285,000 | $ 215,000 | 755,000 | $ 699,000 |
Stock-based compensation cost, unrecognized, related to non-vested options | $ 3,032,000 |  | $ 3,032,000 |  |
Stock-based compensation cost, unrecognized, related to non-vested options, weighted-average period of recognition |  |  | 2 years 1 month 6 days |  |
Incentive stock options granted to 10% shareholders |  |  |  |  |
Stock option details |  |  |  |  |
Maximum exercisable period for options granted |  |  | 5 years |  |

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