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Stock Option Plan - Stock Options Issued (Detail) | 12 Months Ended
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Dec. 31, 2015 USD ($) $ / shares shares | Dec. 31, 2014 USD ($) $ / shares shares | Dec. 31, 2013 USD ($) $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Total grant (in shares) | shares | 1,425,000 |  |
Vested (in shares) | shares | 724,375 |  |
Exercised (in shares) | shares | 265,976 |  |
Forfeited (in shares) | shares | 298,750 |  |
Exercisable at December 31 (in shares) | shares | 435,899 | 380,708 | 413,000
Remaining unexercised (in shares) | shares | 860,274 |  |
Exercise price (in usd per share) | $ / shares | $ 43.67 | $ 37.71 | $ 33.15
Total value at grant date | $ 10,822,000 |  |
Estimated forfeitures | 1,911,000 |  |
Expensed in previous years | 3,588,000 |  |
Future expense | 2,302,000 |  |
Expensed in 2013 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Allocated share based compensation | 880,000 |  |
Expensed in 2014 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Allocated share based compensation | 965,000 |  |
Expensed in 2015 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Allocated share based compensation | 1,176,000 |  |
Directors |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Allocated share based compensation | $ 143,000 | $ 112,900 | $ 124,400
Directors | 5/1/2006 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Total grant (in shares) | shares | 30,000 |  |
Vested (in shares) | shares | 30,000 |  |
Exercised (in shares) | shares | 20,000 |  |
Forfeited (in shares) | shares | 2,500 |  |
Exercisable at December 31 (in shares) | shares | 7,500 |  |
Remaining unexercised (in shares) | shares | 7,500 |  |
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 | $ 144,000 |  |
Expensed in previous years | 144,000 |  |
Future expense | 0 |  |
Directors | 5/1/2006 | Expensed in 2013 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Allocated share based compensation | 0 |  |
Directors | 5/1/2006 | Expensed in 2014 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Allocated share based compensation | 0 |  |
Directors | 5/1/2006 | Expensed in 2015 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Allocated share based compensation | $ 0 |  |
Directors | 4/27/2007 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Total grant (in shares) | shares | 30,000 |  |
Vested (in shares) | shares | 30,000 |  |
Exercised (in shares) | shares | 5,000 |  |
Forfeited (in shares) | shares | 7,500 |  |
Exercisable at December 31 (in shares) | shares | 17,500 |  |
Remaining unexercised (in shares) | shares | 17,500 |  |
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 | $ 285,000 |  |
Expensed in previous years | 285,000 |  |
Future expense | 0 |  |
Directors | 4/27/2007 | Expensed in 2013 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Allocated share based compensation | 0 |  |
Directors | 4/27/2007 | Expensed in 2014 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Allocated share based compensation | 0 |  |
Directors | 4/27/2007 | Expensed in 2015 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Allocated share based compensation | $ 0 |  |
Directors | 4/25/2008 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Total grant (in shares) | shares | 30,000 |  |
Vested (in shares) | shares | 30,000 |  |
Exercised (in shares) | shares | 7,500 |  |
Forfeited (in shares) | shares | 7,500 |  |
Exercisable at December 31 (in shares) | shares | 15,000 |  |
Remaining unexercised (in shares) | shares | 15,000 |  |
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 | $ 255,000 |  |
Expensed in previous years | 255,000 |  |
Future expense | 0 |  |
Directors | 4/25/2008 | Expensed in 2013 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Allocated share based compensation | 0 |  |
Directors | 4/25/2008 | Expensed in 2014 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Allocated share based compensation | 0 |  |
Directors | 4/25/2008 | Expensed in 2015 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Allocated share based compensation | $ 0 |  |
Directors | 4/24/2009 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Total grant (in shares) | shares | 32,500 |  |
Vested (in shares) | shares | 32,500 |  |
Exercised (in shares) | shares | 22,500 |  |
Forfeited (in shares) | shares | 0 |  |
Exercisable at December 31 (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 | $ 223,000 |  |
Expensed in previous years | 223,000 |  |
Future expense | 0 |  |
Directors | 4/24/2009 | Expensed in 2013 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Allocated share based compensation | 0 |  |
Directors | 4/24/2009 | Expensed in 2014 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Allocated share based compensation | 0 |  |
Directors | 4/24/2009 | Expensed in 2015 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Allocated share based compensation | $ 0 |  |
Directors | 5/7/2010 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Total grant (in shares) | shares | 32,500 |  |
Vested (in shares) | shares | 32,500 |  |
Exercised (in shares) | shares | 15,000 |  |
Forfeited (in shares) | shares | 2,500 |  |
Exercisable at December 31 (in shares) | shares | 15,000 |  |
Remaining unexercised (in shares) | shares | 15,000 |  |
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 | $ 288,000 |  |
Expensed in previous years | 288,000 |  |
Future expense | 0 |  |
Directors | 5/7/2010 | Expensed in 2013 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Allocated share based compensation | 0 |  |
Directors | 5/7/2010 | Expensed in 2014 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Allocated share based compensation | 0 |  |
Directors | 5/7/2010 | Expensed in 2015 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Allocated share based compensation | $ 0 |  |
Directors | 5/13/2011 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Total grant (in shares) | shares | 32,500 |  |
Vested (in shares) | shares | 32,500 |  |
Exercised (in shares) | shares | 15,000 |  |
Forfeited (in shares) | shares | 2,500 |  |
Exercisable at December 31 (in shares) | shares | 15,000 |  |
Remaining unexercised (in shares) | shares | 15,000 |  |
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 | $ 297,000 |  |
Expensed in previous years | 297,000 |  |
Future expense | 0 |  |
Directors | 5/13/2011 | Expensed in 2013 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Allocated share based compensation | 0 |  |
Directors | 5/13/2011 | Expensed in 2014 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Allocated share based compensation | 0 |  |
Directors | 5/13/2011 | Expensed in 2015 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Allocated share based compensation | $ 0 |  |
Directors | 5/4/2012 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Total grant (in shares) | shares | 35,000 |  |
Vested (in shares) | shares | 35,000 |  |
Exercised (in shares) | shares | 15,000 |  |
Forfeited (in shares) | shares | 0 |  |
Exercisable at December 31 (in shares) | shares | 20,000 |  |
Remaining unexercised (in shares) | shares | 20,000 |  |
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 | $ 257,000 |  |
Expensed in previous years | 257,000 |  |
Future expense | 0 |  |
Directors | 5/4/2012 | Expensed in 2013 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Allocated share based compensation | 0 |  |
Directors | 5/4/2012 | Expensed in 2014 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Allocated share based compensation | 0 |  |
Directors | 5/4/2012 | Expensed in 2015 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Allocated share based compensation | $ 0 |  |
Directors | 5/10/2013 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Total grant (in shares) | shares | 35,000 |  |
Vested (in shares) | shares | 35,000 |  |
Exercised (in shares) | shares | 12,500 |  |
Forfeited (in shares) | shares | 0 |  |
Exercisable at December 31 (in shares) | shares | 22,500 |  |
Remaining unexercised (in shares) | shares | 22,500 |  |
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 | $ 278,000 |  |
Expensed in previous years | 0 |  |
Future expense | 0 |  |
Directors | 5/10/2013 | Expensed in 2013 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Allocated share based compensation | 278,000 |  |
Directors | 5/10/2013 | Expensed in 2014 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Allocated share based compensation | 0 |  |
Directors | 5/10/2013 | Expensed in 2015 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Allocated share based compensation | $ 0 |  |
Directors | 5/9/2014 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Total grant (in shares) | shares | 30,000 |  |
Vested (in shares) | shares | 30,000 |  |
Exercised (in shares) | shares | 7,500 |  |
Forfeited (in shares) | shares | 0 |  |
Exercisable at December 31 (in shares) | shares | 22,500 |  |
Remaining unexercised (in shares) | shares | 22,500 |  |
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 | $ 110,000 |  |
Expensed in previous years | 0 |  |
Future expense | 0 |  |
Directors | 5/9/2014 | Expensed in 2013 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Allocated share based compensation | 0 |  |
Directors | 5/9/2014 | Expensed in 2014 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Allocated share based compensation | 110,000 |  |
Directors | 5/9/2014 | Expensed in 2015 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Allocated share based compensation | $ 0 |  |
Directors | 5/8/2015 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Total grant (in shares) | shares | 35,000 |  |
Vested (in shares) | shares | 35,000 |  |
Exercised (in shares) | shares | 5,000 |  |
Forfeited (in shares) | shares | 0 |  |
Exercisable at December 31 (in shares) | shares | 30,000 |  |
Remaining unexercised (in shares) | 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 | $ 125,000 |  |
Expensed in previous years | 0 |  |
Future expense | 0 |  |
Directors | 5/8/2015 | Expensed in 2013 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Allocated share based compensation | 0 |  |
Directors | 5/8/2015 | Expensed in 2014 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Allocated share based compensation | 0 |  |
Directors | 5/8/2015 | Expensed in 2015 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Allocated share based compensation | $ 125,000 |  |
Directors | Subtotals |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Total grant (in shares) | shares | 322,500 |  |
Vested (in shares) | shares | 322,500 |  |
Exercised (in shares) | shares | 125,000 |  |
Forfeited (in shares) | shares | 22,500 |  |
Exercisable at December 31 (in shares) | shares | 175,000 |  |
Remaining unexercised (in shares) | shares | 175,000 |  |
Total value at grant date | $ 2,262,000 |  |
Expensed in previous years | 1,749,000 |  |
Future expense | 0 |  |
Directors | Subtotals | Expensed in 2013 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Allocated share based compensation | 278,000 |  |
Directors | Subtotals | Expensed in 2014 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Allocated share based compensation | 110,000 |  |
Directors | Subtotals | Expensed in 2015 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Allocated share based compensation | $ 125,000 |  |
Officers | 4/27/2007 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Total grant (in shares) | shares | 135,000 |  |
Vested (in shares) | shares | 67,500 |  |
Exercised (in shares) | shares | 14,097 |  |
Forfeited (in shares) | shares | 67,500 |  |
Exercisable at December 31 (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 | $ 1,339,000 |  |
Estimated forfeitures | 62,000 |  |
Expensed in previous years | 1,277,000 |  |
Future expense | $ 0 |  |
Weighted average term of remaining future expense | 2 years 7 months 25 days |  |
Officers | 4/27/2007 | Expensed in 2013 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Allocated share based compensation | $ 0 |  |
Officers | 4/27/2007 | Expensed in 2014 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Allocated share based compensation | 0 |  |
Officers | 4/27/2007 | Expensed in 2015 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Allocated share based compensation | $ 0 |  |
Officers | 5/13/2011 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Total grant (in shares) | shares | 162,500 |  |
Vested (in shares) | shares | 118,750 |  |
Exercised (in shares) | shares | 58,754 |  |
Forfeited (in shares) | shares | 43,750 |  |
Exercisable at December 31 (in shares) | shares | 59,996 |  |
Remaining unexercised (in shares) | shares | 59,996 |  |
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 | $ 1,367,000 |  |
Estimated forfeitures | 368,000 |  |
Expensed in previous years | 457,000 |  |
Future expense | 0 |  |
Officers | 5/13/2011 | Expensed in 2013 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Allocated share based compensation | 236,000 |  |
Officers | 5/13/2011 | Expensed in 2014 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Allocated share based compensation | 217,000 |  |
Officers | 5/13/2011 | Expensed in 2015 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Allocated share based compensation | $ 89,000 |  |
Officers | 5/4/2012 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Total grant (in shares) | shares | 242,500 |  |
Vested (in shares) | shares | 81,875 |  |
Exercised (in shares) | shares | 40,625 |  |
Forfeited (in shares) | shares | 135,000 |  |
Exercisable at December 31 (in shares) | shares | 41,250 |  |
Remaining unexercised (in shares) | shares | 66,875 |  |
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 | $ 1,518,000 |  |
Estimated forfeitures | 890,000 |  |
Expensed in previous years | 105,000 |  |
Future expense | 52,000 |  |
Officers | 5/4/2012 | Expensed in 2013 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Allocated share based compensation | 157,000 |  |
Officers | 5/4/2012 | Expensed in 2014 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Allocated share based compensation | 157,000 |  |
Officers | 5/4/2012 | Expensed in 2015 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Allocated share based compensation | $ 157,000 |  |
Officers | 5/10/2013 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Total grant (in shares) | shares | 202,500 |  |
Vested (in shares) | shares | 91,250 |  |
Exercised (in shares) | shares | 24,375 |  |
Forfeited (in shares) | shares | 30,000 |  |
Exercisable at December 31 (in shares) | shares | 66,875 |  |
Remaining unexercised (in shares) | shares | 148,125 |  |
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 | $ 1,401,000 |  |
Estimated forfeitures | 280,000 |  |
Expensed in previous years | 0 |  |
Future expense | 359,000 |  |
Officers | 5/10/2013 | Expensed in 2013 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Allocated share based compensation | 209,000 |  |
Officers | 5/10/2013 | Expensed in 2014 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Allocated share based compensation | 284,000 |  |
Officers | 5/10/2013 | Expensed in 2015 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Allocated share based compensation | $ 269,000 |  |
Officers | 5/9/2014 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Total grant (in shares) | shares | 170,000 |  |
Vested (in shares) | shares | 42,500 |  |
Exercised (in shares) | shares | 3,125 |  |
Forfeited (in shares) | shares | 0 |  |
Exercisable at December 31 (in shares) | shares | 39,375 |  |
Remaining unexercised (in shares) | shares | 166,875 |  |
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 | $ 1,350,000 |  |
Estimated forfeitures | 169,000 |  |
Expensed in previous years | 0 |  |
Future expense | 689,000 |  |
Officers | 5/9/2014 | Expensed in 2013 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Allocated share based compensation | 0 |  |
Officers | 5/9/2014 | Expensed in 2014 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Allocated share based compensation | 197,000 |  |
Officers | 5/9/2014 | Expensed in 2015 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Allocated share based compensation | $ 295,000 |  |
Officers | 5/8/2015 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Total grant (in shares) | shares | 190,000 |  |
Vested (in shares) | shares | 0 |  |
Exercised (in shares) | shares | 0 |  |
Forfeited (in shares) | shares | 0 |  |
Exercisable at December 31 (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 | $ 1,585,000 |  |
Estimated forfeitures | 142,000 |  |
Expensed in previous years | 0 |  |
Future expense | 1,202,000 |  |
Officers | 5/8/2015 | Expensed in 2013 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Allocated share based compensation | 0 |  |
Officers | 5/8/2015 | Expensed in 2014 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Allocated share based compensation | 0 |  |
Officers | 5/8/2015 | Expensed in 2015 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Allocated share based compensation | $ 241,000 |  |
Officers | Subtotals |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Total grant (in shares) | shares | 1,102,500 |  |
Vested (in shares) | shares | 401,875 |  |
Exercised (in shares) | shares | 140,976 |  |
Forfeited (in shares) | shares | 276,250 |  |
Exercisable at December 31 (in shares) | shares | 260,899 |  |
Remaining unexercised (in shares) | shares | 685,274 |  |
Total value at grant date | $ 8,560,000 |  |
Estimated forfeitures | 1,911,000 |  |
Expensed in previous years | 1,839,000 |  |
Future expense | 2,302,000 |  |
Officers | Subtotals | Expensed in 2013 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Allocated share based compensation | 602,000 |  |
Officers | Subtotals | Expensed in 2014 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Allocated share based compensation | 855,000 |  |
Officers | Subtotals | Expensed in 2015 |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Allocated share based compensation | $ 1,051,000 |  |

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