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Stock-Based Compensation - Stock Options by Exercise Price Range (Details)
12 Months Ended
Dec. 31, 2017
$ / shares
shares
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]  
Options Outstanding, Number Outstanding (in shares) | shares 440,642
Options Outstanding, Weighted‑ Average Exercise Price (in USD per share) $ 37.25
Options Exercisable, Number Outstanding (in shares) | shares 127,891
Options Exercisable, Weighted‑ Average Exercise Price (in USD per share) $ 39.91
$20.00-30.00  
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]  
Options Outstanding, Number Outstanding (in shares) | shares 6,383
Options Outstanding, Weighted‑ Average Exercise Price (in USD per share) $ 27.58
Options Outstanding, Weighted‑ Average Remaining Contractual Term (Years) 1 year 3 months
Options Exercisable, Number Outstanding (in shares) | shares 6,383
Options Exercisable, Weighted‑ Average Exercise Price (in USD per share) $ 27.58
Options Exercisable, Weighted‑ Average Remaining Contractual Term (Years) 1 year 3 months
30.01-40.00  
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]  
Options Outstanding, Number Outstanding (in shares) | shares 360,895
Options Outstanding, Weighted‑ Average Exercise Price (in USD per share) $ 33.19
Options Outstanding, Weighted‑ Average Remaining Contractual Term (Years) 5 years 7 months
Options Exercisable, Number Outstanding (in shares) | shares 85,957
Options Exercisable, Weighted‑ Average Exercise Price (in USD per share) $ 33.19
Options Exercisable, Weighted‑ Average Remaining Contractual Term (Years) 5 years 7 months
40.01-50.00  
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]  
Options Outstanding, Number Outstanding (in shares) | shares 5,997
Options Outstanding, Weighted‑ Average Exercise Price (in USD per share) $ 42.59
Options Outstanding, Weighted‑ Average Remaining Contractual Term (Years) 4 years 9 months
Options Exercisable, Number Outstanding (in shares) | shares 3,360
Options Exercisable, Weighted‑ Average Exercise Price (in USD per share) $ 43.14
Options Exercisable, Weighted‑ Average Remaining Contractual Term (Years) 3 years 11 months
50.01-60.00  
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]  
Options Outstanding, Number Outstanding (in shares) | shares 50,428
Options Outstanding, Weighted‑ Average Exercise Price (in USD per share) $ 55.86
Options Outstanding, Weighted‑ Average Remaining Contractual Term (Years) 2 years 6 months
Options Exercisable, Number Outstanding (in shares) | shares 23,407
Options Exercisable, Weighted‑ Average Exercise Price (in USD per share) $ 56.12
Options Exercisable, Weighted‑ Average Remaining Contractual Term (Years) 2 years 6 months
60.01-70.00  
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]  
Options Outstanding, Number Outstanding (in shares) | shares 0
Options Outstanding, Weighted‑ Average Exercise Price (in USD per share) $ 0.00
Options Outstanding, Weighted‑ Average Remaining Contractual Term (Years) 0 years
Options Exercisable, Number Outstanding (in shares) | shares 0
Options Exercisable, Weighted‑ Average Exercise Price (in USD per share) $ 0.00
70.01-80.00  
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]  
Options Outstanding, Number Outstanding (in shares) | shares 16,939
Options Outstanding, Weighted‑ Average Exercise Price (in USD per share) $ 70.14
Options Outstanding, Weighted‑ Average Remaining Contractual Term (Years) 2 years 1 month
Options Exercisable, Number Outstanding (in shares) | shares 8,784
Options Exercisable, Weighted‑ Average Exercise Price (in USD per share) $ 70.14
Options Exercisable, Weighted‑ Average Remaining Contractual Term (Years) 2 years 1 month
Stock Option | $20.00-30.00  
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]  
Range of Exercise Prices, lower range limit (in USD per share) $ 20.00
Range of Exercise Prices, upper range limit (in USD per share) 30.00
Stock Option | 30.01-40.00  
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]  
Range of Exercise Prices, lower range limit (in USD per share) 30.01
Range of Exercise Prices, upper range limit (in USD per share) 40.00
Stock Option | 40.01-50.00  
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]  
Range of Exercise Prices, lower range limit (in USD per share) 40.01
Range of Exercise Prices, upper range limit (in USD per share) 50.00
Stock Option | 50.01-60.00  
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]  
Range of Exercise Prices, lower range limit (in USD per share) 50.01
Range of Exercise Prices, upper range limit (in USD per share) 60.00
Stock Option | 60.01-70.00  
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]  
Range of Exercise Prices, lower range limit (in USD per share) 60.01
Range of Exercise Prices, upper range limit (in USD per share) 70.00
Stock Option | 70.01-80.00  
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]  
Range of Exercise Prices, lower range limit (in USD per share) 70.01
Range of Exercise Prices, upper range limit (in USD per share) $ 80.00