Stock Award Plans (Details) - USD ($) | 12 Months Ended |
Dec. 31, 2015 | Dec. 31, 2014 | Dec. 31, 2013 |
Stock Award Plans [Abstract] | | | |
Compensation cost | $ 11,104,000 | $ 11,591,000 | $ 11,621,000 |
Income tax benefit | $ 4,120,000 | 4,358,000 | 4,370,000 |
Stock Award Plan Information [Abstract] | | | |
Term of grant | 7 years | | |
Vesting period | 3 years | | |
Share-based Compensation Plans Combined Disclosure [Abstract] | | | |
Intrinsic value of stock options exercised | $ 2,555,000 | 11,671,000 | 6,703,000 |
Tax benefit from stock options exercised | 948,000 | 4,388,000 | 2,520,000 |
Intrinsic value of restricted stock vestings | 10,270,000 | 14,847,000 | 10,993,000 |
Tax benefit from restricted stock vesting | 3,810,000 | 5,583,000 | 4,133,000 |
Fair value of options vested | 2,180,000 | 3,759,000 | 3,341,000 |
Fair value of restricted stock vested | $ 10,270,000 | $ 14,847,000 | $ 10,993,000 |
Fair value of stock options granted (in dollars per share) | $ 25.18 | $ 36.05 | $ 25.14 |
Fair value of stock options granted | $ 2,893,000 | $ 4,226,000 | $ 4,184,000 |
Employee Stock Award Plan [Member] | | | |
Stock Award Plan Information [Abstract] | | | |
Shares available for future grants (in shares) | 2,329,238 | | |
Options Exercisable [Abstract] | | | |
Stock options exercisable (in shares) | 239,518 | 157,140 | 175,170 |
Unvested Restricted Stock Award Shares [Roll Forward] | | | |
Nonvested balance beginning of period, Unvested Restricted Stock Award Shares (in shares) | 321,453 | 399,278 | 418,128 |
Granted, Unvested Restricted Stock Award Shares (in shares) | 122,740 | 97,706 | 139,971 |
Vested, Unvested Restricted Stock Award Shares (in shares) | (113,958) | (141,870) | (149,162) |
Forfeited, Unvested Restricted Stock Award Shares (in shares) | (18,508) | (33,661) | (9,659) |
Nonvested balance end of period, Unvested Restricted Stock Award Shares (in shares) | 311,727 | 321,453 | 399,278 |
Weighted Average Grant Date Fair Value Per Share [Abstract] | | | |
Nonvested balance end of period, Weighted Average Grant Date Fair Value Per Share (in dollars per share) | $ 71.04 | $ 54.92 | $ 45.39 |
Granted, Weighted Average Grant Date Fair Value Per Share (in dollars per share) | 75.04 | 97.46 | 69.85 |
Vested, Weighted Average Grant Date Fair Value Per Share (in dollars per share) | 60.73 | 45.64 | 44.30 |
Forfeited, Weighted Average Grant Date Fair Value Per Share (in dollars per share) | 82 | 63.56 | 61.20 |
Nonvested balance end of period, Weighted Average Grant Date Fair Value Per Share (in dollars per share) | 75.73 | $ 71.04 | $ 54.92 |
Employee Stock Award Plan [Member] | First Price Range [Member] | | | |
Outstanding and Exercisable Stock options [Abstract] | | | |
Range of Exercise Prices, upper limit (in dollars per share) | 36.35 | | |
Range of Exercise Prices, lower limit (in dollars per share) | $ 31.35 | | |
Options Outstanding [Abstract] | | | |
Number Outstanding (in shares) | 16,910 | | |
Weighted Average Remaining Contractual Life | 1 year 1 month 6 days | | |
Weighted Average Exercise Price, Options Outstanding (in dollars per share) | $ 32.82 | | |
Options Exercisable [Abstract] | | | |
Number Exercisable (in shares) | 16,910 | | |
Weighted Average Exercise Price, Options Exercisable (in dollars per share) | $ 32.82 | | |
Employee Stock Award Plan [Member] | Second Price Range [Member] | | | |
Outstanding and Exercisable Stock options [Abstract] | | | |
Range of Exercise Prices, upper limit (in dollars per share) | $ 46.74 | | |
Options Outstanding [Abstract] | | | |
Number Outstanding (in shares) | 56,629 | | |
Weighted Average Remaining Contractual Life | 2 years 1 month 6 days | | |
Weighted Average Exercise Price, Options Outstanding (in dollars per share) | $ 46.74 | | |
Options Exercisable [Abstract] | | | |
Number Exercisable (in shares) | 56,629 | | |
Weighted Average Exercise Price, Options Exercisable (in dollars per share) | $ 46.74 | | |
Employee Stock Award Plan [Member] | Third Price Range [Member] | | | |
Outstanding and Exercisable Stock options [Abstract] | | | |
Range of Exercise Prices, upper limit (in dollars per share) | 74.99 | | |
Range of Exercise Prices, lower limit (in dollars per share) | $ 65.28 | | |
Options Outstanding [Abstract] | | | |
Number Outstanding (in shares) | 283,963 | | |
Weighted Average Remaining Contractual Life | 4 years 7 months 6 days | | |
Weighted Average Exercise Price, Options Outstanding (in dollars per share) | $ 70.98 | | |
Options Exercisable [Abstract] | | | |
Number Exercisable (in shares) | 141,669 | | |
Weighted Average Exercise Price, Options Exercisable (in dollars per share) | $ 67.90 | | |
Employee Stock Award Plan [Member] | Fourth Price Range [Member] | | | |
Outstanding and Exercisable Stock options [Abstract] | | | |
Range of Exercise Prices, upper limit (in dollars per share) | 96.85 | | |
Range of Exercise Prices, lower limit (in dollars per share) | $ 93.64 | | |
Options Outstanding [Abstract] | | | |
Number Outstanding (in shares) | 35,763 | | |
Weighted Average Remaining Contractual Life | 5 years 1 month 6 days | | |
Weighted Average Exercise Price, Options Outstanding (in dollars per share) | $ 94.27 | | |
Options Exercisable [Abstract] | | | |
Number Exercisable (in shares) | 11,921 | | |
Weighted Average Exercise Price, Options Exercisable (in dollars per share) | $ 94.27 | | |
Employee Stock Award Plan [Member] | Fifth Price Range [Member] | | | |
Outstanding and Exercisable Stock options [Abstract] | | | |
Range of Exercise Prices, upper limit (in dollars per share) | 114.11 | | |
Range of Exercise Prices, lower limit (in dollars per share) | $ 101.46 | | |
Options Outstanding [Abstract] | | | |
Number Outstanding (in shares) | 37,167 | | |
Weighted Average Remaining Contractual Life | 5 years 2 months 12 days | | |
Weighted Average Exercise Price, Options Outstanding (in dollars per share) | $ 103.22 | | |
Options Exercisable [Abstract] | | | |
Number Exercisable (in shares) | 12,389 | | |
Weighted Average Exercise Price, Options Exercisable (in dollars per share) | $ 103.22 | | |
Employee Stock Award Plan [Member] | Full Exercise Price Range [Member] | | | |
Outstanding and Exercisable Stock options [Abstract] | | | |
Range of Exercise Prices, upper limit (in dollars per share) | 114.11 | | |
Range of Exercise Prices, lower limit (in dollars per share) | $ 31.35 | | |
Options Outstanding [Abstract] | | | |
Number Outstanding (in shares) | 430,432 | | |
Weighted Average Remaining Contractual Life | 4 years 2 months 12 days | | |
Weighted Average Exercise Price, Options Outstanding (in dollars per share) | $ 71.01 | | |
Aggregate Intrinsic Value, Options Outstanding | $ 668,000 | | |
Options Exercisable [Abstract] | | | |
Number Exercisable (in shares) | 239,518 | | |
Weighted Average Exercise Price, Options Exercisable (in dollars per share) | $ 63.56 | | |
Aggregate Intrinsic Value, Options Exercisable | $ 668,000 | | |
2000 Director Plan [Member] | | | |
Stock Award Plan Information [Abstract] | | | |
Term of grant | 10 years | | |
Vesting period | 6 months | | |
Shares available for future grants (in shares) | 539,531 | | |
Options Exercisable [Abstract] | | | |
Stock options exercisable (in shares) | 220,429 | 298,334 | 320,082 |
Unvested Restricted Stock Award Shares [Roll Forward] | | | |
Nonvested balance beginning of period, Unvested Restricted Stock Award Shares (in shares) | 292 | 384 | 348 |
Granted, Unvested Restricted Stock Award Shares (in shares) | 20,350 | 8,160 | 10,536 |
Vested, Unvested Restricted Stock Award Shares (in shares) | (18,851) | (8,252) | (10,500) |
Nonvested balance end of period, Unvested Restricted Stock Award Shares (in shares) | 1,791 | 292 | 384 |
Weighted Average Grant Date Fair Value Per Share [Abstract] | | | |
Nonvested balance end of period, Weighted Average Grant Date Fair Value Per Share (in dollars per share) | $ 99.52 | $ 75.65 | $ 62.99 |
Granted, Weighted Average Grant Date Fair Value Per Share (in dollars per share) | 78.52 | 99.52 | 75.65 |
Vested, Weighted Average Grant Date Fair Value Per Share (in dollars per share) | 79.77 | 98.41 | 75.23 |
Nonvested balance end of period, Weighted Average Grant Date Fair Value Per Share (in dollars per share) | 68.73 | $ 99.52 | $ 75.65 |
2000 Director Plan [Member] | First Price Range [Member] | | | |
Outstanding and Exercisable Stock options [Abstract] | | | |
Range of Exercise Prices, upper limit (in dollars per share) | 36.82 | | |
Range of Exercise Prices, lower limit (in dollars per share) | $ 29.60 | | |
Options Outstanding [Abstract] | | | |
Number Outstanding (in shares) | 30,000 | | |
Weighted Average Remaining Contractual Life | 1 year 10 months 24 days | | |
Weighted Average Exercise Price, Options Outstanding (in dollars per share) | $ 33.60 | | |
Options Exercisable [Abstract] | | | |
Number Exercisable (in shares) | 30,000 | | |
Weighted Average Exercise Price, Options Exercisable (in dollars per share) | $ 33.60 | | |
2000 Director Plan [Member] | Second Price Range [Member] | | | |
Outstanding and Exercisable Stock options [Abstract] | | | |
Range of Exercise Prices, upper limit (in dollars per share) | 56.45 | | |
Range of Exercise Prices, lower limit (in dollars per share) | $ 41.24 | | |
Options Outstanding [Abstract] | | | |
Number Outstanding (in shares) | 71,276 | | |
Weighted Average Remaining Contractual Life | 4 years 3 months 18 days | | |
Weighted Average Exercise Price, Options Outstanding (in dollars per share) | $ 52.34 | | |
Options Exercisable [Abstract] | | | |
Number Exercisable (in shares) | 71,276 | | |
Weighted Average Exercise Price, Options Exercisable (in dollars per share) | $ 52.34 | | |
2000 Director Plan [Member] | Third Price Range [Member] | | | |
Outstanding and Exercisable Stock options [Abstract] | | | |
Range of Exercise Prices, upper limit (in dollars per share) | 62.48 | | |
Range of Exercise Prices, lower limit (in dollars per share) | $ 61.89 | | |
Options Outstanding [Abstract] | | | |
Number Outstanding (in shares) | 41,153 | | |
Weighted Average Remaining Contractual Life | 6 years 6 months | | |
Weighted Average Exercise Price, Options Outstanding (in dollars per share) | $ 62.34 | | |
Options Exercisable [Abstract] | | | |
Number Exercisable (in shares) | 41,153 | | |
Weighted Average Exercise Price, Options Exercisable (in dollars per share) | $ 62.34 | | |
2000 Director Plan [Member] | Fourth Price Range [Member] | | | |
Outstanding and Exercisable Stock options [Abstract] | | | |
Range of Exercise Prices, upper limit (in dollars per share) | 99.52 | | |
Range of Exercise Prices, lower limit (in dollars per share) | $ 75.17 | | |
Options Outstanding [Abstract] | | | |
Number Outstanding (in shares) | 78,000 | | |
Weighted Average Remaining Contractual Life | 7 years 3 months 18 days | | |
Weighted Average Exercise Price, Options Outstanding (in dollars per share) | $ 88.28 | | |
Options Exercisable [Abstract] | | | |
Number Exercisable (in shares) | 78,000 | | |
Weighted Average Exercise Price, Options Exercisable (in dollars per share) | $ 88.28 | | |
2000 Director Plan [Member] | Sixth Price Range [Member] | | | |
Outstanding and Exercisable Stock options [Abstract] | | | |
Range of Exercise Prices, upper limit (in dollars per share) | 99.52 | | |
Range of Exercise Prices, lower limit (in dollars per share) | $ 29.60 | | |
2000 Director Plan [Member] | Full Exercise Price Range [Member] | | | |
Options Outstanding [Abstract] | | | |
Number Outstanding (in shares) | 220,429 | | |
Weighted Average Remaining Contractual Life | 5 years 4 months 24 days | | |
Weighted Average Exercise Price, Options Outstanding (in dollars per share) | $ 64.37 | | |
Aggregate Intrinsic Value, Options Outstanding | $ 775,000 | | |
Options Exercisable [Abstract] | | | |
Number Exercisable (in shares) | 220,429 | | |
Weighted Average Exercise Price, Options Exercisable (in dollars per share) | $ 64.37 | | |
Aggregate Intrinsic Value, Options Exercisable | $ 775,000 | | |
Stock Options [Member] | | | |
Share-based Compensation Plans Combined Disclosure [Abstract] | | | |
Unrecognized compensation cost related to unvested awards | $ 2,956,000 | | |
Weighted average period of recognition in years | 1 year 2 months 12 days | | |
Fair Value Assumptions [Abstract] | | | |
Dividend yield | 0.00% | 0.00% | 0.00% |
Average risk-free interest rate | 1.30% | 2.00% | 1.10% |
Stock price volatility | 33.00% | 33.00% | 34.00% |
Estimated option term | 6 years | | |
Stock Options [Member] | Minimum [Member] | | | |
Fair Value Assumptions [Abstract] | | | |
Estimated option term | | 6 years | 6 years |
Stock Options [Member] | Maximum [Member] | | | |
Fair Value Assumptions [Abstract] | | | |
Estimated option term | | 7 years | 7 years |
Stock Options [Member] | Employee Stock Award Plan [Member] | | | |
Outstanding Non-Qualified or Nonincentive Stock Awards [Roll Forward] | | | |
Outstanding at Period Start, Outstanding Non-Qualified or Nonincentive Stock Awards (in shares) | 322,956 | 379,604 | 351,173 |
Granted, Outstanding Non-Qualified or Nonincentive Stock Awards (in shares) | 114,894 | 75,204 | 111,527 |
Exercised, Outstanding Non-Qualified or Nonincentive Stock Awards (in shares) | 0 | (119,276) | (83,096) |
Canceled or expired, Outstanding Non-Qualified or Nonincentive Stock Awards (in shares) | (7,418) | (12,576) | 0 |
Outstanding at Period End, Outstanding Non-Qualified or Nonincentive Stock Awards (in shares) | 430,432 | 322,956 | 379,604 |
Weighted Average Exercise Price [Abstract] | | | |
Outstanding at Period Start, Weighted Average Exercise Price (in dollars per share) | $ 69.95 | $ 55.42 | $ 45.54 |
Granted, Weighted Average Exercise Price (in dollars per share) | 74.99 | 98.91 | 70.94 |
Exercised, Weighted Average Exercise Price (in dollars per share) | 0 | 42.07 | 34.51 |
Canceled or expired, Weighted Average Exercise Price (in dollars per share) | 86.28 | 68.89 | 0 |
Outstanding at Period End, Weighted Average Exercise Price (in dollars per share) | $ 71.01 | $ 69.95 | $ 55.42 |
Stock Options [Member] | 2000 Director Plan [Member] | | | |
Outstanding Non-Qualified or Nonincentive Stock Awards [Roll Forward] | | | |
Outstanding at Period Start, Outstanding Non-Qualified or Nonincentive Stock Awards (in shares) | 298,334 | 320,322 | 345,938 |
Granted, Outstanding Non-Qualified or Nonincentive Stock Awards (in shares) | 0 | 42,000 | 54,958 |
Exercised, Outstanding Non-Qualified or Nonincentive Stock Awards (in shares) | (77,905) | (63,988) | (80,574) |
Outstanding at Period End, Outstanding Non-Qualified or Nonincentive Stock Awards (in shares) | 220,429 | 298,334 | 320,322 |
Weighted Average Exercise Price [Abstract] | | | |
Outstanding at Period Start, Weighted Average Exercise Price (in dollars per share) | $ 60.01 | $ 50.64 | $ 45.84 |
Granted, Weighted Average Exercise Price (in dollars per share) | 0 | 99.52 | 75.17 |
Exercised, Weighted Average Exercise Price (in dollars per share) | 47.65 | 39.08 | 46.75 |
Outstanding at Period End, Weighted Average Exercise Price (in dollars per share) | $ 64.37 | $ 60.01 | $ 50.64 |
Restricted Stock [Member] | | | |
Share-based Compensation Plans Combined Disclosure [Abstract] | | | |
Unrecognized compensation cost related to unvested awards | $ 16,920,000 | | |
Weighted average period of recognition in years | 2 years 9 months 18 days | | |