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Stock Option Plans - Stock Options Issued (Details) | 3 Months Ended
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Mar. 31, 2019 USD ($) $ / shares shares
Share Based Compensation Arrangements By Share Based Payment Award Options [Line Items] |
Total grant (in shares) | 1,904,000
Vested (in shares) | 1,174,500
Exercised (in shares) | 566,081
Forfeited (in shares) | 231,250
Exercisable at end of period (in shares) | 593,419
Remaining unexercised (in shares) | 1,106,669
Exercise price (in usd per share) | $ / shares | $ 0.00
Total value at grant date | $ | $ 13,059,865
Estimated forfeitures | $ | 1,727,338
Expensed in previous years | $ | 9,001,988
Expensed in 2019 | $ | 396,542
Future expense | $ | $ 1,933,997
Weighted average term of remaining future expense (in years) | 2 years 4 months 11 days
Directors |
Share Based Compensation Arrangements By Share Based Payment Award Options [Line Items] |
Total grant (in shares) | 320,000
Vested (in shares) | 320,000
Exercised (in shares) | 170,000
Forfeited (in shares) | 15,000
Exercisable at end of period (in shares) | 135,000
Remaining unexercised (in shares) | 135,000
Total value at grant date | $ | $ 2,064,650
Expensed in previous years | $ | 2,064,650
Expensed in 2019 | $ | 0
Future expense | $ | $ 0
Directors | 4/24/2009 |
Share Based Compensation Arrangements By Share Based Payment Award Options [Line Items] |
Total grant (in shares) | 32,500
Vested (in shares) | 32,500
Exercised (in shares) | 30,000
Forfeited (in shares) | 0
Exercisable at end of period (in shares) | 2,500
Remaining unexercised (in shares) | 2,500
Exercise price (in usd per share) | $ / shares | $ 32.68
Volatility (percentage) | 0.344
Expected life (years) | 6 years
Assumed yield (percentage) | 4.54%
Risk-free rate (percentage) | 2.19%
Total value at grant date | $ | $ 222,950
Expensed in previous years | $ | 222,950
Expensed in 2019 | $ | 0
Future expense | $ | $ 0
Directors | 5/7/2010 |
Share Based Compensation Arrangements By Share Based Payment Award Options [Line Items] |
Total grant (in shares) | 32,500
Vested (in shares) | 32,500
Exercised (in shares) | 27,500
Forfeited (in shares) | 2,500
Exercisable at end of period (in shares) | 2,500
Remaining unexercised (in shares) | 2,500
Exercise price (in usd per share) | $ / shares | $ 38.76
Volatility (percentage) | 0.369
Expected life (years) | 5 years
Assumed yield (percentage) | 4.23%
Risk-free rate (percentage) | 2.17%
Total value at grant date | $ | $ 287,950
Expensed in previous years | $ | 287,950
Expensed in 2019 | $ | 0
Future expense | $ | $ 0
Directors | 5/13/2011 |
Share Based Compensation Arrangements By Share Based Payment Award Options [Line Items] |
Total grant (in shares) | 32,500
Vested (in shares) | 32,500
Exercised (in shares) | 25,000
Forfeited (in shares) | 2,500
Exercisable at end of period (in shares) | 5,000
Remaining unexercised (in shares) | 5,000
Exercise price (in usd per share) | $ / shares | $ 41.82
Volatility (percentage) | 0.358
Expected life (years) | 5 years
Assumed yield (percentage) | 4.16%
Risk-free rate (percentage) | 1.86%
Total value at grant date | $ | $ 297,375
Expensed in previous years | $ | 297,375
Expensed in 2019 | $ | 0
Future expense | $ | $ 0
Directors | 5/4/2012 |
Share Based Compensation Arrangements By Share Based Payment Award Options [Line Items] |
Total grant (in shares) | 35,000
Vested (in shares) | 35,000
Exercised (in shares) | 25,000
Forfeited (in shares) | 0
Exercisable at end of period (in shares) | 10,000
Remaining unexercised (in shares) | 10,000
Exercise price (in usd per share) | $ / shares | $ 39.29
Volatility (percentage) | 0.348
Expected life (years) | 5 years
Assumed yield (percentage) | 4.61%
Risk-free rate (percentage) | 0.78%
Total value at grant date | $ | $ 257,250
Expensed in previous years | $ | 257,250
Expensed in 2019 | $ | 0
Future expense | $ | $ 0
Directors | 5/10/2013 |
Share Based Compensation Arrangements By Share Based Payment Award Options [Line Items] |
Total grant (in shares) | 35,000
Vested (in shares) | 35,000
Exercised (in shares) | 22,500
Forfeited (in shares) | 0
Exercisable at end of period (in shares) | 12,500
Remaining unexercised (in shares) | 12,500
Exercise price (in usd per share) | $ / shares | $ 44.42
Volatility (percentage) | 0.333
Expected life (years) | 5 years
Assumed yield (percentage) | 4.53%
Risk-free rate (percentage) | 0.82%
Total value at grant date | $ | $ 278,250
Expensed in previous years | $ | 278,250
Expensed in 2019 | $ | 0
Future expense | $ | $ 0
Directors | 5/9/2014 |
Share Based Compensation Arrangements By Share Based Payment Award Options [Line Items] |
Total grant (in shares) | 30,000
Vested (in shares) | 30,000
Exercised (in shares) | 17,500
Forfeited (in shares) | 0
Exercisable at end of period (in shares) | 12,500
Remaining unexercised (in shares) | 12,500
Exercise price (in usd per share) | $ / shares | $ 47.03
Volatility (percentage) | 0.173
Expected life (years) | 5 years
Assumed yield (percentage) | 4.48%
Risk-free rate (percentage) | 1.63%
Total value at grant date | $ | $ 109,500
Expensed in previous years | $ | 109,500
Expensed in 2019 | $ | 0
Future expense | $ | $ 0
Directors | 5/8/2015 |
Share Based Compensation Arrangements By Share Based Payment Award Options [Line Items] |
Total grant (in shares) | 35,000
Vested (in shares) | 35,000
Exercised (in shares) | 12,500
Forfeited (in shares) | 2,500
Exercisable at end of period (in shares) | 20,000
Remaining unexercised (in shares) | 20,000
Exercise price (in usd per share) | $ / shares | $ 51.07
Volatility (percentage) | 0.166
Expected life (years) | 5 years
Assumed yield (percentage) | 4.54%
Risk-free rate (percentage) | 1.50%
Total value at grant date | $ | $ 125,300
Expensed in previous years | $ | 125,300
Expensed in 2019 | $ | 0
Future expense | $ | $ 0
Directors | 5/6/2016 |
Share Based Compensation Arrangements By Share Based Payment Award Options [Line Items] |
Total grant (in shares) | 32,500
Vested (in shares) | 32,500
Exercised (in shares) | 7,500
Forfeited (in shares) | 2,500
Exercisable at end of period (in shares) | 22,500
Remaining unexercised (in shares) | 22,500
Exercise price (in usd per share) | $ / shares | $ 57.74
Volatility (percentage) | 0.166
Expected life (years) | 5 years
Assumed yield (percentage) | 3.75%
Risk-free rate (percentage) | 1.23%
Total value at grant date | $ | $ 151,125
Expensed in previous years | $ | 151,125
Expensed in 2019 | $ | 0
Future expense | $ | $ 0
Directors | 5/5/2017 |
Share Based Compensation Arrangements By Share Based Payment Award Options [Line Items] |
Total grant (in shares) | 27,500
Vested (in shares) | 27,500
Exercised (in shares) | 0
Forfeited (in shares) | 5,000
Exercisable at end of period (in shares) | 22,500
Remaining unexercised (in shares) | 22,500
Exercise price (in usd per share) | $ / shares | $ 59.41
Volatility (percentage) | 0.173
Expected life (years) | 5 years
Assumed yield (percentage) | 3.45%
Risk-free rate (percentage) | 1.89%
Total value at grant date | $ | $ 165,550
Expensed in previous years | $ | 165,550
Expensed in 2019 | $ | 0
Future expense | $ | $ 0
Directors | 5/11/2018 |
Share Based Compensation Arrangements By Share Based Payment Award Options [Line Items] |
Total grant (in shares) | 27,500
Vested (in shares) | 27,500
Exercised (in shares) | 2,500
Forfeited (in shares) | 0
Exercisable at end of period (in shares) | 25,000
Remaining unexercised (in shares) | 25,000
Exercise price (in usd per share) | $ / shares | $ 49.46
Volatility (percentage) | 0.192
Expected life (years) | 5 years
Assumed yield (percentage) | 3.70%
Risk-free rate (percentage) | 2.84%
Total value at grant date | $ | $ 169,400
Expensed in previous years | $ | 169,400
Expensed in 2019 | $ | 0
Future expense | $ | $ 0
Officers |
Share Based Compensation Arrangements By Share Based Payment Award Options [Line Items] |
Total grant (in shares) | 1,584,000
Vested (in shares) | 854,500
Exercised (in shares) | 396,081
Forfeited (in shares) | 216,250
Exercisable at end of period (in shares) | 458,419
Remaining unexercised (in shares) | 971,669
Total value at grant date | $ | $ 10,995,215
Estimated forfeitures | $ | 1,727,338
Expensed in previous years | $ | 6,937,338
Expensed in 2019 | $ | 396,542
Future expense | $ | $ 1,933,997
Officers | 5/13/2011 |
Share Based Compensation Arrangements By Share Based Payment Award Options [Line Items] |
Total grant (in shares) | 162,500
Vested (in shares) | 118,750
Exercised (in shares) | 103,750
Forfeited (in shares) | 43,750
Exercisable at end of period (in shares) | 15,000
Remaining unexercised (in shares) | 15,000
Exercise price (in usd per share) | $ / shares | $ 41.82
Volatility (percentage) | 0.330
Expected life (years) | 8 years
Assumed yield (percentage) | 4.81%
Risk-free rate (percentage) | 2.75%
Total value at grant date | $ | $ 1,366,625
Estimated forfeitures | $ | 367,937
Expensed in previous years | $ | 998,688
Expensed in 2019 | $ | 0
Future expense | $ | $ 0
Officers | 5/4/2012 |
Share Based Compensation Arrangements By Share Based Payment Award Options [Line Items] |
Total grant (in shares) | 242,500
Vested (in shares) | 107,500
Exercised (in shares) | 92,455
Forfeited (in shares) | 135,000
Exercisable at end of period (in shares) | 15,045
Remaining unexercised (in shares) | 15,045
Exercise price (in usd per share) | $ / shares | $ 39.29
Volatility (percentage) | 0.315
Expected life (years) | 8 years
Assumed yield (percentage) | 5.28%
Risk-free rate (percentage) | 1.49%
Total value at grant date | $ | $ 1,518,050
Estimated forfeitures | $ | 845,100
Expensed in previous years | $ | 672,950
Expensed in 2019 | $ | 0
Future expense | $ | $ 0
Officers | 5/10/2013 |
Share Based Compensation Arrangements By Share Based Payment Award Options [Line Items] |
Total grant (in shares) | 202,500
Vested (in shares) | 171,875
Exercised (in shares) | 129,375
Forfeited (in shares) | 30,625
Exercisable at end of period (in shares) | 42,500
Remaining unexercised (in shares) | 42,500
Exercise price (in usd per share) | $ / shares | $ 44.42
Volatility (percentage) | 0.304
Expected life (years) | 8 years
Assumed yield (percentage) | 5.12%
Risk-free rate (percentage) | 1.49%
Total value at grant date | $ | $ 1,401,300
Estimated forfeitures | $ | 211,925
Expensed in previous years | $ | 1,189,375
Expensed in 2019 | $ | 0
Future expense | $ | $ 0
Officers | 5/9/2014 |
Share Based Compensation Arrangements By Share Based Payment Award Options [Line Items] |
Total grant (in shares) | 170,000
Vested (in shares) | 168,125
Exercised (in shares) | 46,126
Forfeited (in shares) | 1,875
Exercisable at end of period (in shares) | 121,999
Remaining unexercised (in shares) | 121,999
Exercise price (in usd per share) | $ / shares | $ 47.03
Volatility (percentage) | 0.306
Expected life (years) | 7 years
Assumed yield (percentage) | 4.89%
Risk-free rate (percentage) | 2.17%
Total value at grant date | $ | $ 1,349,800
Estimated forfeitures | $ | 14,887
Expensed in previous years | $ | 1,334,913
Expensed in 2019 | $ | 0
Future expense | $ | $ 0
Officers | 5/8/2015 |
Share Based Compensation Arrangements By Share Based Payment Award Options [Line Items] |
Total grant (in shares) | 190,000
Vested (in shares) | 140,625
Exercised (in shares) | 20,625
Forfeited (in shares) | 3,125
Exercisable at end of period (in shares) | 120,000
Remaining unexercised (in shares) | 166,250
Exercise price (in usd per share) | $ / shares | $ 51.07
Volatility (percentage) | 0.298
Expected life (years) | 7 years
Assumed yield (percentage) | 4.94%
Risk-free rate (percentage) | 1.89%
Total value at grant date | $ | $ 1,584,600
Estimated forfeitures | $ | 26,062
Expensed in previous years | $ | 1,322,596
Expensed in 2019 | $ | 176,957
Future expense | $ | $ 58,985
Officers | 5/6/2016 |
Share Based Compensation Arrangements By Share Based Payment Award Options [Line Items] |
Total grant (in shares) | 194,000
Vested (in shares) | 96,375
Exercised (in shares) | 3,750
Forfeited (in shares) | 1,875
Exercisable at end of period (in shares) | 92,625
Remaining unexercised (in shares) | 188,375
Exercise price (in usd per share) | $ / shares | $ 57.74
Volatility (percentage) | 0.185
Expected life (years) | 7 years
Assumed yield (percentage) | 3.80%
Risk-free rate (percentage) | 1.55%
Total value at grant date | $ | $ 1,136,840
Estimated forfeitures | $ | 86,628
Expensed in previous years | $ | 700,128
Expensed in 2019 | $ | 65,637
Future expense | $ | $ 284,447
Officers | 5/5/2017 |
Share Based Compensation Arrangements By Share Based Payment Award Options [Line Items] |
Total grant (in shares) | 205,000
Vested (in shares) | 51,250
Exercised (in shares) | 0
Forfeited (in shares) | 0
Exercisable at end of period (in shares) | 51,250
Remaining unexercised (in shares) | 205,000
Exercise price (in usd per share) | $ / shares | $ 59.41
Volatility (percentage) | 0.170
Expected life (years) | 7 years
Assumed yield (percentage) | 3.50%
Risk-free rate (percentage) | 2.17%
Total value at grant date | $ | $ 1,324,300
Estimated forfeitures | $ | 91,642
Expensed in previous years | $ | 513,600
Expensed in 2019 | $ | 77,040
Future expense | $ | $ 642,018
Officers | 5/11/2018 |
Share Based Compensation Arrangements By Share Based Payment Award Options [Line Items] |
Total grant (in shares) | 217,500
Vested (in shares) | 0
Exercised (in shares) | 0
Forfeited (in shares) | 0
Exercisable at end of period (in shares) | 0
Remaining unexercised (in shares) | 217,500
Exercise price (in usd per share) | $ / shares | $ 49.46
Volatility (percentage) | 0.177
Expected life (years) | 7 years
Assumed yield (percentage) | 3.75%
Risk-free rate (percentage) | 2.94%
Total value at grant date | $ | $ 1,313,700
Estimated forfeitures | $ | 83,157
Expensed in previous years | $ | 205,088
Expensed in 2019 | $ | 76,908
Future expense | $ | $ 948,547

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