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Stock-Based Compensation (Details) - USD ($)
12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Percentage of eligible earnings to purchase common stock through the employee stock purchase plan (in hundredths) 10.00%    
Discount rate to the average closing price at which employees may purchase stock (in hundredths) 5.00%    
Stock based compensation expense $ 61,800,000 $ 63,000,000 $ 53,400,000
Tax effect recognized in net income 21,600,000 22,100,000 18,700,000
Windfall tax benefit, net $ 22,200,000 $ 21,500,000 $ 16,000,000
Weighted average assumptions used in calculating the weighted average fair value of options granted      
Weighted average fair value of options granted (per share) $ 33.98 $ 34.95 $ 37.08
Risk-free interest rate (%) (in hundredths) 1.53% 1.63% 0.86%
Average expected option life (in years) 5 years 1 month 6 days 5 years 2 months 19 days 5 years 2 months 8 days
Expected volatility (%) (in hundredths) 22.17% 27.01% 36.09%
Expected dividend yield (%) (in hundredths) 0.62% 0.58% 0.56%
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]      
Number of shares outstanding, beginning balance (in shares) 2,981,111 2,988,436  
Number of shares granted (in shares) 628,155 650,000  
Options Exercised (in shares) (400,050) (587,661)  
Number of shares canceled (in shares) (91,600) (69,664)  
Number of shares outstanding, ending balance (in shares) 3,117,616 2,981,111 2,988,436
Number of shares, options, exercisable, number (in shares) 1,935,351    
Weighted Average Exercise Price [Abstract]      
Weighted average exercise price per share outstanding, beginning balance (in dollars per share) $ 90.48 $ 74.00  
Weighted average exercise price per share granted (in dollars per share) 162.77 137.05  
Weighted average exercise price per share exercised (in dollars per share) 82.50 55.98  
Weighted average exercise price per share cancelled (in dollars per share) 142.36 116.29  
Weighted average exercise price per share outstanding, ending balance (in dollars per share) $ 104.54 $ 90.48 $ 74.00
Weighted average remaining contractual term of options outstanding (in years) 6 years 29 days 6 years 4 months 13 days  
Aggregate intrinsic value of options outstanding $ 265,782,636 $ 196,378,239  
Options, Exercisable, Weighted Average Exercise Price (in dollars per share) $ 78.76    
Options, Exercisable, Weighted Average Remaining Contractual Term (in years) 4 years 6 months 18 days    
Options, Exercisable, Aggregate intrinsic value $ 214,879,670    
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]      
Total unrecognized compensation expense related to nonvested restricted stock granted to both employees and directors $ 26,500,000    
Weighted-average period over which unrecognized compensation costs on non-vested stock options are expected to be recognized (in years) 1 year 10 months 24 days    
Intrinsic value of options exercised $ 36,900,000 50,300,000 $ 28,800,000
Cash received from option exercises under all plans $ 33,000,000 $ 32,500,000  
Summary of nonvested shares activity [Rollforward]      
Non-vested shares outstanding, beginning of period (in shares) 542,555 573,850  
Nonvested shares granted (in shares) 437,035 375,060  
Nonvested shares vested (in shares) (243,423) (378,994)  
Nonvested shares forfeited (in shares) (26,892) (27,361)  
Nonvested shares outstanding, end of period (in shares) 709,275 542,555 573,850
Restricted Stock Awards [Abstract]      
Weighted average fair value of nonvested shares, beginning of period (in dollars per share) $ 130.29 $ 103.44  
Weighted Average Restricted Award Grant Date Fair Value (in dollars per share) 159.32 142.30  
Weighted average fair value of shares vested (in dollars per share) 183.10 153.16  
Weighted average fair value of nonvested shares forfeited (in dollars per share) 148.82 106.60  
Weighted average fair value of nonvested shares, end of period (in dollars per share) $ 183.90 $ 130.29 $ 103.44
Total unrecognized compensation expense related to nonvested restricted stock granted to both employees and directors $ 62,200,000    
Restricted Awards Outstanding, Weighted Average Remaining Contractual Terms 2 years 4 months 24 days    
Employee Stock Purchase Plan      
Shares of stock purchased during the period by participants in the employee stock purchase plan (in shares) 18,132 20,368 20,211
Amount paid for stock purchased during the period by participants in the employee stock purchase plan $ 2,900,000 $ 2,800,000 $ 2,400,000
Employee Stock Ownership Plan (ESOP), Compensation Expense $ 0 0 0
Earliest [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Percentage of market value at which stock option are granted (in hundredths) 100.00%    
Employee Stock Options [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Stock based compensation expense $ 15,300,000 16,600,000 16,900,000
Expiration period (in years) 10 years    
Employee Stock Options [Member] | Earliest [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Vesting period (in years) 3 years    
Employee Stock Options [Member] | Latest [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Vesting period (in years) 5 years    
Restricted Stock [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Stock based compensation expense $ 46,500,000 $ 46,400,000 $ 36,500,000
Restricted Stock [Member] | Earliest [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Vesting period (in years) 1 year    
Restricted Stock [Member] | Latest [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Vesting period (in years) 3 years    
Exercise Price Range 1 [Member]      
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]      
Exercise price range, lower range limit (in dollars per share) $ 38.46    
Exercise price range, upper range limit (in dollars per share) $ 57.68    
Options outstanding (in shares) 896,590    
Average exercise price of options outstanding (in dollars per share) $ 53.04    
Average remaining life of options outstanding (in years) 2 years 4 months 24 days    
Exercisable options (in shares) 896,590    
Average exercise price of exercisable options (in dollars per share) $ 53.04    
Exercise Price Range 2 [Member]      
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]      
Exercise price range, lower range limit (in dollars per share) 57.69    
Exercise price range, upper range limit (in dollars per share) $ 76.91    
Options outstanding (in shares) 298,733    
Average exercise price of options outstanding (in dollars per share) $ 72.65    
Average remaining life of options outstanding (in years) 5 years 1 month 6 days    
Exercisable options (in shares) 298,733    
Average exercise price of exercisable options (in dollars per share) $ 72.65    
Exercise Price Range 3 [Member]      
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]      
Exercise price range, lower range limit (in dollars per share) 76.92    
Exercise price range, upper range limit (in dollars per share) $ 96.14    
Options outstanding (in shares) 295,684    
Average exercise price of options outstanding (in dollars per share) $ 93.16    
Average remaining life of options outstanding (in years) 6 years 1 month 6 days    
Exercisable options (in shares) 294,434    
Average exercise price of exercisable options (in dollars per share) $ 93.15    
Exercise Price Range 4 [Member]      
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]      
Exercise price range, lower range limit (in dollars per share) 96.15    
Exercise price range, upper range limit (in dollars per share) $ 115.37    
Options outstanding (in shares) 310,597    
Average exercise price of options outstanding (in dollars per share) $ 114.82    
Average remaining life of options outstanding (in years) 7 years    
Exercisable options (in shares) 200,319    
Average exercise price of exercisable options (in dollars per share) $ 114.60    
Exercise Price Range 5 [Member]      
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]      
Exercise price range, lower range limit (in dollars per share) 115.38    
Exercise price range, upper range limit (in dollars per share) $ 134.60    
Options outstanding (in shares) 562,626    
Average exercise price of options outstanding (in dollars per share) $ 130.96    
Average remaining life of options outstanding (in years) 8 years    
Exercisable options (in shares) 195,520    
Average exercise price of exercisable options (in dollars per share) $ 130.52    
Exercise Price Range 6 [Member]      
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]      
Exercise price range, lower range limit (in dollars per share) 134.61    
Exercise price range, upper range limit (in dollars per share) $ 153.82    
Options outstanding (in shares) 272,036    
Average exercise price of options outstanding (in dollars per share) $ 144.28    
Average remaining life of options outstanding (in years) 8 years 8 months 12 days    
Exercisable options (in shares) 37,422    
Average exercise price of exercisable options (in dollars per share) $ 142.12    
Exercise Price Range 7 [Member]      
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]      
Exercise price range, lower range limit (in dollars per share) 153.83    
Exercise price range, upper range limit (in dollars per share) $ 173.05    
Options outstanding (in shares) 413,350    
Average exercise price of options outstanding (in dollars per share) $ 165.00    
Average remaining life of options outstanding (in years) 9 years 2 months 12 days    
Exercisable options (in shares) 11,000    
Average exercise price of exercisable options (in dollars per share) $ 156.57    
Exercise Price Range 8 [Member]      
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]      
Exercise price range, lower range limit (in dollars per share) 173.06    
Exercise price range, upper range limit (in dollars per share) $ 192.28    
Options outstanding (in shares) 68,000    
Average exercise price of options outstanding (in dollars per share) $ 181.14    
Average remaining life of options outstanding (in years) 9 years 8 months 12 days    
Exercisable options (in shares) 1,333    
Average exercise price of exercisable options (in dollars per share) $ 175.00    
Exercise Price Range 9 [Member]      
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]      
Exercise price range, lower range limit (in dollars per share) 38.46    
Exercise price range, upper range limit (in dollars per share) $ 192.28    
Options outstanding (in shares) 3,117,616    
Average exercise price of options outstanding (in dollars per share) $ 104.54    
Average remaining life of options outstanding (in years) 6 years 1 month 6 days    
Exercisable options (in shares) 1,935,351    
Average exercise price of exercisable options (in dollars per share) $ 78.76    
2006 Plan [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Number of shares reserved for issuance 14,000,000    
Shares available for grant (in shares) 3,175,605    
2000 Plan [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Number of shares reserved for issuance 17,000