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Stock Options (Details) - USD ($) | 12 Months Ended |
--- | --- | ---
Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017 | Apr. 05, 2012
Stock options under 2012 Plan |  |  |  |
Stock option details |  |  |  |
Shares available for future grants | 28,651 |  |  | 800,000
Maximum exercisable period for options granted | 10 years |  |  |
Black-Scholes-Merton option valuation model assumptions |  |  |  |
Expected Life (Years) | 7 years | 7 years |  |
Dividend yield (as a percent) | 2.93% | 1.73% |  |
Interest rate (as a percent) | 1.97% | 2.68% |  |
Volatility (as a percent) | 26.97% | 31.65% |  |
Number of options granted (in shares) | 16,500 |  | 0 |
Stock option activity |  |  |  |
Options outstanding at the beginning of the period (in shares) | 788,977 |  |  |
Plus: Options granted (in shares) | 16,500 |  | 0 |
Less: |  |  |  |
Exercise of stock options (in shares) | 110,938 |  |  |
Options forfeited (in shares) | 35,951 |  |  |
Options outstanding at the end of the period (in shares) | 658,588 | 788,977 |  |
Options fully vested and exercisable at the end of the period (in shares) | 319,085 |  |  |
Stock Options, Weighted average exercise price |  |  |  |
Options outstanding at the beginning, weighted average exercise price (in dollars per share) | $ 25.91 |  |  |
Plus: Options granted, weighted average exercise price (in dollars per share) | 35.34 |  |  |
Less: |  |  |  |
Options exercised, weighted average exercise price (in dollars per share) | 17.29 |  |  |
Options forfeited, weighted average exercise price (in dollars per share) | 26.74 |  |  |
Options outstanding at the end, weighted average exercise price (in dollars per share) | 27.55 | $ 25.91 |  |
Options fully vested and exercisable at the end, weighted average exercise price (in dollars per share) | $ 22.14 |  |  |
Stock Options, Weighted average remaining contractual term (years) |  |  |  |
Options outstanding at the end, weighted average remaining contractual term (years) | 5 years 9 months 3 days |  |  |
Options fully vested and exercisable at the end, weighted average remaining contractual term (years) | 4 years 4 months 17 days |  |  |
Stock Options, Aggregate intrinsic value |  |  |  |
Options outstanding at the end, aggregate intrinsic value | $ 10,219,000 |  |  |
Options fully vested and exercisable at the end, aggregate intrinsic value | 6,680,000 |  |  |
Stock-based compensation expense | 980,000 | $ 1,035,000 | $ 903,000 |
Stock-based compensation cost, unrecognized, related to non-vested options | $ 1,922,000 |  |  |
Stock-based compensation cost, unrecognized, related to non-vested options, weighted-average period of recognition | 1 year 10 months 24 days |  |  |
Other information pertaining to option activity |  |  |  |
Weighted average grant date fair value of stock options granted (in dollars per share) | $ 7.38 | $ 11.78 |  |
Total fair value of stock options vested | $ 1,333,000 | $ 1,077,000 | 1,182,000 |
Total intrinsic value of stock options exercised | $ 2,373,000 | $ 2,045,000 | $ 2,595,000 |
Incentive stock options granted to 10% shareholders |  |  |  |
Stock option details |  |  |  |
Maximum exercisable period for options granted | 5 years |  |  |

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- Definition The estimated measure of the percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (f)(2)(ii) -URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901 + Details
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