Stock Award Plans (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Feb. 15, 2012
Stock Award Plans [Abstract]
Compensation cost	$ 9,796,000	$ 9,228,000	$ 10,867,000
Income tax benefit	3,644,000	3,534,000	4,162,000
Share-based Compensation Plans Combined Disclosure [Abstract]
Intrinsic value of stock options exercised	6,768,000	4,072,000	2,835,000
Tax benefit from stock options exercised	2,518,000	1,560,000	1,086,000
Intrinsic value of restricted stock vestings	11,878,000	7,921,000	8,809,000
Tax benefit from restricted stock vesting	4,418,000	3,034,000	3,374,000
Fair value of options vested	2,846,000	2,618,000	3,491,000
Fair value of restricted stock vested	11,878,000	7,921,000	8,809,000
Fair value of stock options granted (in dollars per share)	$ 22.21	$ 18.84	$ 13.81
Fair value of stock options granted	3,691,000	3,081,000	2,231,000
Employee Stock Award Plan [Member]
Stock Award Plan Information [Abstract]
Shares available for future grants (in shares)	2,909,458
Number of shares authorized under the plan (in shares)				3,000,000
Number of shares authorized after the amendment under the plan (in shares)				5,000,000
Elected director first grant vesting period	The options granted when first elected a director vest immediately
Options Exercisable [Abstract]
Stock options exercisable	149,544	226,900	200,210
Unvested Restricted Stock Award Shares [Roll Forward]
Nonvested balance beginning of period, Unvested Restricted Stock Award Shares	475,632	499,335	542,679
Granted, Unvested Restricted Stock Award Shares (in shares)	121,953	150,612	197,994
Vested, Unvested Restricted Stock Award Shares (in shares)	(168,166)	(163,480)	(234,831)
Forfeited, Unvested Restricted Stock Award Shares (in shares)	(11,291)	(10,835)	(6,507)
Nonvested balance end of period, Unvested Restricted Stock Award Shares	418,128	475,632	499,335
Weighted Average Grant Date Fair Value Per Share [Abstract]
Nonvested balance beginning of period, Weighted Average Grant Date Fair Value Per Share	$ 36.43	$ 31.98	$ 30.70
Granted, Weighted Average Grant Date Fair Value Per Share (in dollars per share)	$ 67.79	$ 46.50	$ 33.42
Vested, Weighted Average Grant Date Fair Value Per Share (in dollars per share)	$ 35.43	$ 33.27	$ 39.34
Forfeited, Weighted Average Grant Date Fair Value Per Share (in dollars per share)	$ 58.64	$ 38.90	$ 32.00
Nonvested balance end of period, Weighted Average Grant Date Fair Value Per Share	$ 45.39	$ 36.43	$ 31.98
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)	$ 32.56
Range of Exercise Prices, lower limit (in dollars per share)	$ 23.98
Options Outstanding [Abstract]
Number Outstanding (in shares)	126,698
Weighted Average Remaining Contractual Life (in years)	3 years 6 months
Weighted Average Exercise Price, Options Outstanding (in dollars per share)	$ 30.67
Options Exercisable [Abstract]
Number Exercisable (in shares)	93,363
Weighted Average Exercise Price, Options Exercisable (in dollars per share)	$ 30.03
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)	$ 36.35
Range of Exercise Prices, lower limit (in dollars per share)	$ 34.4
Options Outstanding [Abstract]
Number Outstanding (in shares)	24,000
Weighted Average Remaining Contractual Life (in years)	1 year 4 months 24 days
Weighted Average Exercise Price, Options Outstanding (in dollars per share)	$ 34.73
Options Exercisable [Abstract]
Number Exercisable (in shares)	22,666
Weighted Average Exercise Price, Options Exercisable (in dollars per share)	$ 34.63
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)	$ 46.74
Options Outstanding [Abstract]
Number Outstanding (in shares)	100,569
Weighted Average Remaining Contractual Life (in years)	5 years
Weighted Average Exercise Price, Options Outstanding (in dollars per share)	$ 46.74
Options Exercisable [Abstract]
Number Exercisable (in shares)	33,515
Weighted Average Exercise Price, Options Exercisable (in dollars per share)	$ 46.74
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)	$ 66.72
Range of Exercise Prices, lower limit (in dollars per share)	$ 65.28
Options Outstanding [Abstract]
Number Outstanding (in shares)	99,906
Weighted Average Remaining Contractual Life (in years)	6 years 1 month 6 days
Weighted Average Exercise Price, Options Outstanding (in dollars per share)	$ 65.80
Options Exercisable [Abstract]
Number Exercisable (in shares)	0
Weighted Average Exercise Price, Options Exercisable (in dollars per share)	$ 0
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)	$ 66.72
Range of Exercise Prices, lower limit (in dollars per share)	$ 23.98
Options Outstanding [Abstract]
Number Outstanding (in shares)	351,173
Weighted Average Remaining Contractual Life (in years)	4 years 6 months
Weighted Average Exercise Price, Options Outstanding (in dollars per share)	$ 45.54
Aggregate Intrinsic Value, Options Outstanding	5,741,000
Options Exercisable [Abstract]
Number Exercisable (in shares)	149,544
Weighted Average Exercise Price, Options Exercisable (in dollars per share)	$ 34.47
Aggregate Intrinsic Value, Options Exercisable	4,100,000
2000 Director Plan [Member]
Stock Award Plan Information [Abstract]
Term of grant	10 years
Shares available for future grants (in shares)	675,535
Number of shares authorized under the plan (in shares)				1,000,000
Number of shares authorized after the amendment under the plan (in shares)				1,500,000
Options Exercisable [Abstract]
Stock options exercisable	345,360	352,987	355,555
Unvested Restricted Stock Award Shares [Roll Forward]
Nonvested balance beginning of period, Unvested Restricted Stock Award Shares	1,748	525	732
Granted, Unvested Restricted Stock Award Shares (in shares)	10,383	11,990	11,097
Vested, Unvested Restricted Stock Award Shares (in shares)	(11,783)	(10,767)	(11,304)
Nonvested balance end of period, Unvested Restricted Stock Award Shares	348	1,748	525
Weighted Average Grant Date Fair Value Per Share [Abstract]
Nonvested balance beginning of period, Weighted Average Grant Date Fair Value Per Share	$ 58.07	$ 41.33	$ 29.77
Granted, Weighted Average Grant Date Fair Value Per Share (in dollars per share)	$ 62.99	$ 56.85	$ 41.33
Vested, Weighted Average Grant Date Fair Value Per Share (in dollars per share)	$ 62.26	$ 55.90	$ 40.58
Nonvested balance end of period, Weighted Average Grant Date Fair Value Per Share	$ 62.99	$ 58.07	$ 41.33
2000 Director Plan [Member] | First Price Range [Member]
Outstanding and Exercisable Stock options [Abstract]
Range of Exercise Prices, upper limit (in dollars per share)	$ 12.69
Range of Exercise Prices, lower limit (in dollars per share)	$ 17.88
Options Outstanding [Abstract]
Number Outstanding (in shares)	24,000
Weighted Average Remaining Contractual Life (in years)	9 months 18 days
Weighted Average Exercise Price, Options Outstanding (in dollars per share)	$ 15.29
Options Exercisable [Abstract]
Number Exercisable (in shares)	24,000
Weighted Average Exercise Price, Options Exercisable (in dollars per share)	$ 15.29
2000 Director Plan [Member] | Second Price Range [Member]
Outstanding and Exercisable Stock options [Abstract]
Range of Exercise Prices, upper limit (in dollars per share)	$ 20.28
Range of Exercise Prices, lower limit (in dollars per share)	$ 29.60
Options Outstanding [Abstract]
Number Outstanding (in shares)	36,000
Weighted Average Remaining Contractual Life (in years)	5 years
Weighted Average Exercise Price, Options Outstanding (in dollars per share)	$ 26.49
Options Exercisable [Abstract]
Number Exercisable (in shares)	36,000
Weighted Average Exercise Price, Options Exercisable (in dollars per share)	$ 26.49
2000 Director Plan [Member] | Third Price Range [Member]
Outstanding and Exercisable Stock options [Abstract]
Range of Exercise Prices, upper limit (in dollars per share)	$ 35.17
Range of Exercise Prices, lower limit (in dollars per share)	$ 36.82
Options Outstanding [Abstract]
Number Outstanding (in shares)	62,036
Weighted Average Remaining Contractual Life (in years)	3 years 8 months 12 days
Weighted Average Exercise Price, Options Outstanding (in dollars per share)	$ 35.84
Options Exercisable [Abstract]
Number Exercisable (in shares)	62,036
Weighted Average Exercise Price, Options Exercisable (in dollars per share)	$ 35.84
2000 Director Plan [Member] | Fourth Price Range [Member]
Outstanding and Exercisable Stock options [Abstract]
Range of Exercise Prices, upper limit (in dollars per share)	$ 41.24
Range of Exercise Prices, lower limit (in dollars per share)	$ 56.45
Options Outstanding [Abstract]
Number Outstanding (in shares)	157,596
Weighted Average Remaining Contractual Life (in years)	7 years
Weighted Average Exercise Price, Options Outstanding (in dollars per share)	$ 51.89
Options Exercisable [Abstract]
Number Exercisable (in shares)	157,596
Weighted Average Exercise Price, Options Exercisable (in dollars per share)	$ 51.89
2000 Director Plan [Member] | Fifth Price Range [Member]
Outstanding and Exercisable Stock options [Abstract]
Range of Exercise Prices, upper limit (in dollars per share)	$ 61.89
Range of Exercise Prices, lower limit (in dollars per share)	$ 62.48
Options Outstanding [Abstract]
Number Outstanding (in shares)	66,306
Weighted Average Remaining Contractual Life (in years)	7 years 10 months 24 days
Weighted Average Exercise Price, Options Outstanding (in dollars per share)	$ 62.39
Options Exercisable [Abstract]
Number Exercisable (in shares)	65,728
Weighted Average Exercise Price, Options Exercisable (in dollars per share)	$ 62.39
2000 Director Plan [Member] | Full Exercise Price Range [Member]
Outstanding and Exercisable Stock options [Abstract]
Range of Exercise Prices, upper limit (in dollars per share)	$ 12.69
Range of Exercise Prices, lower limit (in dollars per share)	$ 62.48
Options Outstanding [Abstract]
Number Outstanding (in shares)	345,938
Weighted Average Remaining Contractual Life (in years)	6 years
Weighted Average Exercise Price, Options Outstanding (in dollars per share)	$ 45.84
Aggregate Intrinsic Value, Options Outstanding	5,551,000
Options Exercisable [Abstract]
Number Exercisable (in shares)	345,360
Weighted Average Exercise Price, Options Exercisable (in dollars per share)	$ 45.81
Aggregate Intrinsic Value, Options Exercisable	5,552,000
Employee Stock Award Plan - Options Granted After to January 25, 2010 [Member]
Stock Award Plan Information [Abstract]
Term of grant	7 years
Vesting period	3 years
Employee Stock Award Plan - Options Granted Prior to January 25, 2010 [Member]
Stock Award Plan Information [Abstract]
Term of grant	5 years
Vesting period	3 years
Stock Options [Member]
Share-based Compensation Plans Combined Disclosure [Abstract]
Unrecognized compensation cost related to unvested awards	2,151,000
Weighted average period of recognition in years	1 year 3 months 18 days
Fair Value Assumptions [Abstract]
Dividend yield (in hundredths)	0.00%	0.00%	0.00%
Average risk-free interest rate (in hundredths)	1.10%	2.40%	3.10%
Stock price volatility (in hundredths)	33.00%	33.00%	33.00%
Stock Options [Member] | Minimum [Member]
Fair Value Assumptions [Abstract]
Estimated option term (in years)	6 years	6 years	6 years
Stock Options [Member] | Maximum [Member]
Fair Value Assumptions [Abstract]
Estimated option term (in years)	7 years	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)	445,674	434,447	640,483
Granted, Outstanding Non-Qualified or Nonincentive Stock Awards	99,906	103,021	103,999
Exercised, Outstanding Non-Qualified or Nonincentive Stock Awards	(191,955)	(91,794)	(228,543)
Canceled or expired, Outstanding Non-Qualified or Nonincentive Stock Awards	(2,452)	0	(81,492)
Outstanding at Period End, Outstanding Non-Qualified or Nonincentive Stock Awards (in shares)	351,173	445,674	434,447
Weighted Average Exercise Price [Abstract]
Outstanding at Period Start, Weighted Average Exercise Price (in dollars per share)	$ 36.81	$ 33.53	$ 33.39
Granted, Weighted Average Exercise Price (in dollars per share)	$ 65.80	$ 47.01	$ 32.60
Exercised, Weighted Average Exercise Price (in dollars per share)	$ 35.65	$ 32.75	$ 28.36
Canceled or expired, Weighted Average Exercise Price (in dollars per share)	$ 58.28	$ 0	$ 45.73
Outstanding at Period End, Weighted Average Exercise Price (in dollars per share)	$ 45.54	$ 36.81	$ 33.53
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)	353,625	356,429	301,937
Granted, Outstanding Non-Qualified or Nonincentive Stock Awards	66,306	60,552	57,492
Exercised, Outstanding Non-Qualified or Nonincentive Stock Awards	(73,993)	(63,356)	(3,000)
Outstanding at Period End, Outstanding Non-Qualified or Nonincentive Stock Awards (in shares)	345,938	353,625	356,429
Weighted Average Exercise Price [Abstract]
Outstanding at Period Start, Weighted Average Exercise Price (in dollars per share)	$ 39.05	$ 34.88	$ 33.43
Granted, Weighted Average Exercise Price (in dollars per share)	$ 62.39	$ 56.42	$ 41.24
Exercised, Weighted Average Exercise Price (in dollars per share)	$ 28.22	$ 32.17	$ 10.67
Outstanding at Period End, Weighted Average Exercise Price (in dollars per share)	$ 45.84	$ 39.05	$ 34.88
Restricted Stock [Member]
Share-based Compensation Plans Combined Disclosure [Abstract]
Unrecognized compensation cost related to unvested awards	$ 13,706,000
Weighted average period of recognition in years	2 years 7 months 6 days