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Stock Option Plans - Stock Options Issued (Details) | 9 Months Ended
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Sep. 30, 2016 USD ($) $ / shares shares
Share Based Compensation Arrangements By Share Based Payment Award Options [Line Items] |
Total grant (in shares) | 1,621,500
Vested (in shares) | 883,125
Exercised (in shares) | 460,932
Forfeited (in shares) | 296,250
Exercisable at end of period (in shares) | 402,193
Remaining unexercised (in shares) | 864,318
Exercise price (in usd per share) | $ / shares | $ 45.99
Total value at grant date | $ | $ 11,966,115
Estimated forfeitures | $ | 1,952,662
Expensed in previous years | $ | 6,465,083
Expensed in 2016 | $ | 1,051,286
Future expense | $ | $ 2,497,084
Weighted average term of remaining future expense (in years) | 2 years 7 months 23 days
Directors |
Share Based Compensation Arrangements By Share Based Payment Award Options [Line Items] |
Total grant (in shares) | 325,000
Vested (in shares) | 325,000
Exercised (in shares) | 130,000
Forfeited (in shares) | 20,000
Exercisable at end of period (in shares) | 175,000
Remaining unexercised (in shares) | 175,000
Total value at grant date | $ | $ 2,269,700
Expensed in previous years | $ | 2,118,575
Expensed in 2016 | $ | 151,125
Future expense | $ | $ 0
Directors | 4/27/2007 |
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) | 10,000
Forfeited (in shares) | 7,500
Exercisable at end of period (in shares) | 12,500
Remaining unexercised (in shares) | 12,500
Exercise price (in usd per share) | $ / shares | $ 54.17
Volatility | 0.225
Expected life (years) | 8 years
Assumed yield | 4.39%
Risk-free rate | 4.65%
Total value at grant date | $ | $ 285,300
Expensed in previous years | $ | 285,300
Expensed in 2016 | $ | 0
Future expense | $ | $ 0
Directors | 4/25/2008 |
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) | 12,500
Forfeited (in shares) | 7,500
Exercisable at end of period (in shares) | 10,000
Remaining unexercised (in shares) | 10,000
Exercise price (in usd per share) | $ / shares | $ 50.15
Volatility | 0.237
Expected life (years) | 7 years
Assumed yield | 4.09%
Risk-free rate | 3.49%
Total value at grant date | $ | $ 254,700
Expensed in previous years | $ | 254,700
Expensed in 2016 | $ | 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) | 25,000
Forfeited (in shares) | 0
Exercisable at end of period (in shares) | 7,500
Remaining unexercised (in shares) | 7,500
Exercise price (in usd per share) | $ / shares | $ 32.68
Volatility | 0.344
Expected life (years) | 6 years
Assumed yield | 4.54%
Risk-free rate | 2.19%
Total value at grant date | $ | $ 222,950
Expensed in previous years | $ | 222,950
Expensed in 2016 | $ | 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) | 17,500
Forfeited (in shares) | 2,500
Exercisable at end of period (in shares) | 12,500
Remaining unexercised (in shares) | 12,500
Exercise price (in usd per share) | $ / shares | $ 38.76
Volatility | 0.369
Expected life (years) | 5 years
Assumed yield | 4.23%
Risk-free rate | 2.17%
Total value at grant date | $ | $ 287,950
Expensed in previous years | $ | 287,950
Expensed in 2016 | $ | 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) | 17,500
Forfeited (in shares) | 2,500
Exercisable at end of period (in shares) | 12,500
Remaining unexercised (in shares) | 12,500
Exercise price (in usd per share) | $ / shares | $ 41.82
Volatility | 0.358
Expected life (years) | 5 years
Assumed yield | 4.16%
Risk-free rate | 1.86%
Total value at grant date | $ | $ 297,375
Expensed in previous years | $ | 297,375
Expensed in 2016 | $ | 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) | 17,500
Forfeited (in shares) | 0
Exercisable at end of period (in shares) | 17,500
Remaining unexercised (in shares) | 17,500
Exercise price (in usd per share) | $ / shares | $ 39.29
Volatility | 0.348
Expected life (years) | 5 years
Assumed yield | 4.61%
Risk-free rate | 0.78%
Total value at grant date | $ | $ 257,250
Expensed in previous years | $ | 257,250
Expensed in 2016 | $ | 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) | 15,000
Forfeited (in shares) | 0
Exercisable at end of period (in shares) | 20,000
Remaining unexercised (in shares) | 20,000
Exercise price (in usd per share) | $ / shares | $ 44.42
Volatility | 0.333
Expected life (years) | 5 years
Assumed yield | 4.53%
Risk-free rate | 0.82%
Total value at grant date | $ | $ 278,250
Expensed in previous years | $ | 278,250
Expensed in 2016 | $ | 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) | 10,000
Forfeited (in shares) | 0
Exercisable at end of period (in shares) | 20,000
Remaining unexercised (in shares) | 20,000
Exercise price (in usd per share) | $ / shares | $ 47.03
Volatility | 0.173
Expected life (years) | 5 years
Assumed yield | 4.48%
Risk-free rate | 1.63%
Total value at grant date | $ | $ 109,500
Expensed in previous years | $ | 109,500
Expensed in 2016 | $ | 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) | 5,000
Forfeited (in shares) | 0
Exercisable at end of period (in shares) | 30,000
Remaining unexercised (in shares) | 30,000
Exercise price (in usd per share) | $ / shares | $ 51.07
Volatility | 0.166
Expected life (years) | 5 years
Assumed yield | 4.54%
Risk-free rate | 1.50%
Total value at grant date | $ | $ 125,300
Expensed in previous years | $ | 125,300
Expensed in 2016 | $ | 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) | 0
Forfeited (in shares) | 0
Exercisable at end of period (in shares) | 32,500
Remaining unexercised (in shares) | 32,500
Exercise price (in usd per share) | $ / shares | $ 57.74
Volatility | 0.166
Expected life (years) | 5 years
Assumed yield | 3.75%
Risk-free rate | 1.23%
Total value at grant date | $ | $ 151,125
Expensed in previous years | $ | 0
Expensed in 2016 | $ | 151,125
Future expense | $ | $ 0
Officers |
Share Based Compensation Arrangements By Share Based Payment Award Options [Line Items] |
Total grant (in shares) | 1,296,500
Vested (in shares) | 558,125
Exercised (in shares) | 330,932
Forfeited (in shares) | 276,250
Exercisable at end of period (in shares) | 227,193
Remaining unexercised (in shares) | 689,318
Total value at grant date | $ | $ 9,696,415
Estimated forfeitures | $ | 1,952,662
Expensed in previous years | $ | 4,346,508
Expensed in 2016 | $ | 900,161
Future expense | $ | $ 2,497,084
Officers | 4/27/2007 |
Share Based Compensation Arrangements By Share Based Payment Award Options [Line Items] |
Total grant (in shares) | 135,000
Vested (in shares) | 67,500
Exercised (in shares) | 67,500
Forfeited (in shares) | 67,500
Exercisable at end of period (in shares) | 0
Remaining unexercised (in shares) | 0
Exercise price (in usd per share) | $ / shares | $ 54.17
Volatility | 0.233
Expected life (years) | 6 years 6 months
Assumed yield | 4.13%
Risk-free rate | 4.61%
Total value at grant date | $ | $ 1,339,200
Estimated forfeitures | $ | 62,000
Expensed in previous years | $ | 1,277,200
Expensed in 2016 | $ | 0
Future expense | $ | $ 0
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) | 92,915
Forfeited (in shares) | 43,750
Exercisable at end of period (in shares) | 25,835
Remaining unexercised (in shares) | 25,835
Exercise price (in usd per share) | $ / shares | $ 41.82
Volatility | 0.330
Expected life (years) | 8 years
Assumed yield | 4.81%
Risk-free rate | 2.75%
Total value at grant date | $ | $ 1,366,625
Estimated forfeitures | $ | 367,937
Expensed in previous years | $ | 998,688
Expensed in 2016 | $ | 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) | 76,142
Forfeited (in shares) | 135,000
Exercisable at end of period (in shares) | 31,358
Remaining unexercised (in shares) | 31,358
Exercise price (in usd per share) | $ / shares | $ 39.29
Volatility | 0.315
Expected life (years) | 8 years
Assumed yield | 5.28%
Risk-free rate | 1.49%
Total value at grant date | $ | $ 1,518,050
Estimated forfeitures | $ | 845,100
Expensed in previous years | $ | 575,994
Expensed in 2016 | $ | 96,956
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) | 131,875
Exercised (in shares) | 63,750
Forfeited (in shares) | 30,000
Exercisable at end of period (in shares) | 68,125
Remaining unexercised (in shares) | 108,750
Exercise price (in usd per share) | $ / shares | $ 44.42
Volatility | 0.304
Expected life (years) | 8 years
Assumed yield | 5.12%
Risk-free rate | 1.49%
Total value at grant date | $ | $ 1,401,300
Estimated forfeitures | $ | 280,468
Expensed in previous years | $ | 762,034
Expensed in 2016 | $ | 201,825
Future expense | $ | $ 156,973
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) | 85,000
Exercised (in shares) | 25,000
Forfeited (in shares) | 0
Exercisable at end of period (in shares) | 60,000
Remaining unexercised (in shares) | 145,000
Exercise price (in usd per share) | $ / shares | $ 47.03
Volatility | 0.306
Expected life (years) | 7 years
Assumed yield | 4.89%
Risk-free rate | 2.17%
Total value at grant date | $ | $ 1,349,800
Estimated forfeitures | $ | 168,749
Expensed in previous years | $ | 492,120
Expensed in 2016 | $ | 221,454
Future expense | $ | $ 467,477
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) | 47,500
Exercised (in shares) | 5,625
Forfeited (in shares) | 0
Exercisable at end of period (in shares) | 41,875
Remaining unexercised (in shares) | 184,375
Exercise price (in usd per share) | $ / shares | $ 51.07
Volatility | 0.298
Expected life (years) | 7 years
Assumed yield | 4.94%
Risk-free rate | 1.89%
Total value at grant date | $ | $ 1,584,600
Estimated forfeitures | $ | 141,780
Expensed in previous years | $ | 240,472
Expensed in 2016 | $ | 270,531
Future expense | $ | $ 931,817
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) | 0
Exercised (in shares) | 0
Forfeited (in shares) | 0
Exercisable at end of period (in shares) | 0
Remaining unexercised (in shares) | 194,000
Exercise price (in usd per share) | $ / shares | $ 57.74
Volatility | 0.185
Expected life (years) | 7 years
Assumed yield | 3.80%
Risk-free rate | 1.55%
Total value at grant date | $ | $ 1,136,840
Estimated forfeitures | $ | 86,628
Expensed in previous years | $ | 0
Expensed in 2016 | $ | 109,395
Future expense | $ | $ 940,817

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