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Stock Option Plans - Stock Options Issued (Details) | 9 Months Ended
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Sep. 30, 2015 USD ($) $ / shares shares
Share Based Compensation Arrangements By Share Based Payment Award Options [Line Items] |
Exercisable at end of period (in shares) | shares | 476,524
Exercise price (in usd per share) | $ / shares | $ 42.71
Weighted average term of remaining future expense (in years) | 2 years 10 months 6 days
Directors | 5/1/2006 |
Share Based Compensation Arrangements By Share Based Payment Award Options [Line Items] |
Grant date | May 01, 2006
Total grant (in shares) | shares | 30,000
Vested (in shares) | $ 30,000
Exercised (in shares) | shares | 15,000
Forfeited (in shares) | shares | 2,500
Exercisable at end of period (in shares) | shares | 12,500
Remaining unexercised (in shares) | shares | 12,500
Exercise price (in usd per share) | $ / shares | $ 40.35
Volatility | 0.206
Expected life (years) | 9 years
Assumed yield | 5.93%
Risk-free rate | 5.11%
Total value at grant date | $ 143,400
Expensed in previous years | 143,400
Expensed in 2015 | 0
Future expense | $ 0
Directors | 4/27/2007 |
Share Based Compensation Arrangements By Share Based Payment Award Options [Line Items] |
Grant date | Apr. 27, 2007
Total grant (in shares) | shares | 30,000
Vested (in shares) | $ 30,000
Exercised (in shares) | shares | 2,500
Forfeited (in shares) | shares | 7,500
Exercisable at end of period (in shares) | shares | 20,000
Remaining unexercised (in shares) | shares | 20,000
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 2015 | 0
Future expense | $ 0
Directors | 4/25/2008 |
Share Based Compensation Arrangements By Share Based Payment Award Options [Line Items] |
Grant date | Apr. 25, 2008
Total grant (in shares) | shares | 30,000
Vested (in shares) | $ 30,000
Exercised (in shares) | shares | 2,500
Forfeited (in shares) | shares | 7,500
Exercisable at end of period (in shares) | shares | 20,000
Remaining unexercised (in shares) | shares | 20,000
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 2015 | 0
Future expense | $ 0
Directors | 4/24/2009 |
Share Based Compensation Arrangements By Share Based Payment Award Options [Line Items] |
Grant date | Apr. 24, 2009
Total grant (in shares) | shares | 32,500
Vested (in shares) | $ 32,500
Exercised (in shares) | shares | 22,500
Forfeited (in shares) | shares | 0
Exercisable at end of period (in shares) | shares | 10,000
Remaining unexercised (in shares) | shares | 10,000
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 2015 | 0
Future expense | $ 0
Directors | 5/7/2010 |
Share Based Compensation Arrangements By Share Based Payment Award Options [Line Items] |
Grant date | May 07, 2010
Total grant (in shares) | shares | 32,500
Vested (in shares) | $ 32,500
Exercised (in shares) | shares | 12,500
Forfeited (in shares) | shares | 2,500
Exercisable at end of period (in shares) | shares | 17,500
Remaining unexercised (in shares) | shares | 17,500
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 2015 | 0
Future expense | $ 0
Directors | 5/13/2011 |
Share Based Compensation Arrangements By Share Based Payment Award Options [Line Items] |
Grant date | May 13, 2011
Total grant (in shares) | shares | 32,500
Vested (in shares) | $ 32,500
Exercised (in shares) | shares | 12,500
Forfeited (in shares) | shares | 2,500
Exercisable at end of period (in shares) | shares | 17,500
Remaining unexercised (in shares) | shares | 17,500
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 2015 | 0
Future expense | $ 0
Directors | 5/4/2012 |
Share Based Compensation Arrangements By Share Based Payment Award Options [Line Items] |
Grant date | May 04, 2012
Total grant (in shares) | shares | 35,000
Vested (in shares) | $ 35,000
Exercised (in shares) | shares | 12,500
Forfeited (in shares) | shares | 0
Exercisable at end of period (in shares) | shares | 22,500
Remaining unexercised (in shares) | shares | 22,500
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 2015 | 0
Future expense | $ 0
Directors | 5/10/2013 |
Share Based Compensation Arrangements By Share Based Payment Award Options [Line Items] |
Grant date | May 10, 2013
Total grant (in shares) | shares | 35,000
Vested (in shares) | $ 35,000
Exercised (in shares) | shares | 10,000
Forfeited (in shares) | shares | 0
Exercisable at end of period (in shares) | shares | 25,000
Remaining unexercised (in shares) | shares | 25,000
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 2015 | 0
Future expense | $ 0
Directors | 5/9/2014 |
Share Based Compensation Arrangements By Share Based Payment Award Options [Line Items] |
Grant date | May 09, 2014
Total grant (in shares) | shares | 30,000
Vested (in shares) | $ 30,000
Exercised (in shares) | shares | 2,500
Forfeited (in shares) | shares | 0
Exercisable at end of period (in shares) | shares | 27,500
Remaining unexercised (in shares) | shares | 27,500
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 2015 | 0
Future expense | $ 0
Directors | 5/8/2015 |
Share Based Compensation Arrangements By Share Based Payment Award Options [Line Items] |
Grant date | May 08, 2015
Total grant (in shares) | shares | 35,000
Vested (in shares) | $ 35,000
Exercised (in shares) | shares | 0
Forfeited (in shares) | shares | 0
Exercisable at end of period (in shares) | shares | 35,000
Remaining unexercised (in shares) | shares | 35,000
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 | 0
Expensed in 2015 | 125,300
Future expense | $ 0
Directors | Subtotals |
Share Based Compensation Arrangements By Share Based Payment Award Options [Line Items] |
Total grant (in shares) | shares | 322,500
Vested (in shares) | $ 322,500
Exercised (in shares) | shares | 92,500
Forfeited (in shares) | shares | 22,500
Exercisable at end of period (in shares) | shares | 207,500
Remaining unexercised (in shares) | shares | 207,500
Total value at grant date | $ 2,261,975
Expensed in previous years | 2,136,675
Expensed in 2015 | 125,300
Future expense | $ 0
Officers |
Share Based Compensation Arrangements By Share Based Payment Award Options [Line Items] |
Total grant (in shares) | shares | 1,425,000
Vested (in shares) | $ 724,375
Exercised (in shares) | shares | 225,351
Forfeited (in shares) | shares | 298,750
Exercisable at end of period (in shares) | shares | 476,524
Remaining unexercised (in shares) | shares | 900,899
Total value at grant date | $ 10,821,550
Estimated forfeitures | 1,910,624
Expensed in previous years | 5,432,122
Expensed in 2015 | 905,818
Future expense | $ 2,572,986
Officers | 4/27/2007 |
Share Based Compensation Arrangements By Share Based Payment Award Options [Line Items] |
Grant date | Apr. 27, 2007
Total grant (in shares) | shares | 135,000
Vested (in shares) | $ 67,500
Exercised (in shares) | shares | 14,097
Forfeited (in shares) | shares | 67,500
Exercisable at end of period (in shares) | shares | 53,403
Remaining unexercised (in shares) | shares | 53,403
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 2015 | 0
Future expense | $ 0
Officers | 5/13/2011 |
Share Based Compensation Arrangements By Share Based Payment Award Options [Line Items] |
Grant date | May 13, 2011
Total grant (in shares) | shares | 162,500
Vested (in shares) | $ 118,750
Exercised (in shares) | shares | 57,504
Forfeited (in shares) | shares | 43,750
Exercisable at end of period (in shares) | shares | 61,246
Remaining unexercised (in shares) | shares | 61,246
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 | 909,563
Expensed in 2015 | 89,125
Future expense | $ 0
Officers | 5/4/2012 |
Share Based Compensation Arrangements By Share Based Payment Award Options [Line Items] |
Grant date | May 04, 2012
Total grant (in shares) | shares | 242,500
Vested (in shares) | $ 81,875
Exercised (in shares) | shares | 38,750
Forfeited (in shares) | shares | 135,000
Exercisable at end of period (in shares) | shares | 43,125
Remaining unexercised (in shares) | shares | 68,750
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 | 889,690
Expensed in previous years | 418,899
Expensed in 2015 | 117,819
Future expense | $ 91,642
Officers | 5/10/2013 |
Share Based Compensation Arrangements By Share Based Payment Award Options [Line Items] |
Grant date | May 10, 2013
Total grant (in shares) | shares | 202,500
Vested (in shares) | $ 91,250
Exercised (in shares) | shares | 21,875
Forfeited (in shares) | shares | 30,000
Exercisable at end of period (in shares) | shares | 69,375
Remaining unexercised (in shares) | shares | 150,625
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 | 492,937
Expensed in 2015 | 201,825
Future expense | $ 426,070
Officers | 5/9/2014 |
Share Based Compensation Arrangements By Share Based Payment Award Options [Line Items] |
Grant date | May 09, 2014
Total grant (in shares) | shares | 170,000
Vested (in shares) | $ 42,500
Exercised (in shares) | shares | 625
Forfeited (in shares) | shares | 0
Exercisable at end of period (in shares) | shares | 41,875
Remaining unexercised (in shares) | shares | 169,375
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 | 196,848
Expensed in 2015 | 221,454
Future expense | $ 762,749
Officers | 5/8/2015 |
Share Based Compensation Arrangements By Share Based Payment Award Options [Line Items] |
Grant date | May 08, 2015
Total grant (in shares) | shares | 190,000
Vested (in shares) | $ 0
Exercised (in shares) | shares | 0
Forfeited (in shares) | shares | 0
Exercisable at end of period (in shares) | shares | 0
Remaining unexercised (in shares) | shares | 190,000
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 | 0
Expensed in 2015 | 150,295
Future expense | $ 1,292,525
Officers | Subtotals |
Share Based Compensation Arrangements By Share Based Payment Award Options [Line Items] |
Total grant (in shares) | shares | 1,102,500
Vested (in shares) | $ 401,875
Exercised (in shares) | shares | 132,851
Forfeited (in shares) | shares | 276,250
Exercisable at end of period (in shares) | shares | 269,024
Remaining unexercised (in shares) | shares | 693,399
Total value at grant date | $ 8,559,575
Estimated forfeitures | 1,910,624
Expensed in previous years | 3,295,447
Expensed in 2015 | 780,518
Future expense | $ 2,572,986

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