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Share-Based Compensation (Stock Options Outstanding Per Range of Exercise Prices) (Details) - Stock Options
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 1,110,918
Options Outstanding, Weighted Average Exercise Price Per Share (USD per share) $ 29.56
Options Outstanding, Weighted Average Contractual Term 6 years 5 months 1 day
Options Exercisable, Weighted Average Exercise Price Per Share (USD per share) $ 25.99
Options Exercisable, Weighted Average Contractual Term 5 years 6 months 21 days
Minimum  
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]  
Exercise price per share, lower price range limit (USD per share) $ 11.09
Maximum  
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]  
Exercise price per share, upper price range limit (USD per share) $ 53.72
$11.09 - 12.80  
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]  
Options Outstanding, Number Outstanding (in shares) | shares 32,691
Options Outstanding, Weighted Average Exercise Price Per Share (USD per share) $ 12.37
Options Outstanding, Weighted Average Contractual Term 2 years 11 months 6 days
Options Exercisable, Number Exercisable (in shares) | shares 32,691
Options Exercisable, Weighted Average Exercise Price Per Share (USD per share) $ 12.37
Options Exercisable, Weighted Average Contractual Term 2 years 11 months 6 days
$11.09 - 12.80 | Minimum  
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]  
Exercise price per share, lower price range limit (USD per share) $ 11.09
$11.09 - 12.80 | Maximum  
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]  
Exercise price per share, upper price range limit (USD per share) $ 12.8
$13.20 - 16.24  
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]  
Options Outstanding, Number Outstanding (in shares) | shares 136,604
Options Outstanding, Weighted Average Exercise Price Per Share (USD per share) $ 15.94
Options Outstanding, Weighted Average Contractual Term 4 years 11 months 2 days
Options Exercisable, Number Exercisable (in shares) | shares 136,604
Options Exercisable, Weighted Average Exercise Price Per Share (USD per share) $ 15.94
Options Exercisable, Weighted Average Contractual Term 4 years 11 months 2 days
$13.20 - 16.24 | Minimum  
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]  
Exercise price per share, lower price range limit (USD per share) $ 13.2
$13.20 - 16.24 | Maximum  
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]  
Exercise price per share, upper price range limit (USD per share) $ 16.24
$19.97 - 21.10  
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]  
Options Outstanding, Number Outstanding (in shares) | shares 49,546
Options Outstanding, Weighted Average Exercise Price Per Share (USD per share) $ 20.36
Options Outstanding, Weighted Average Contractual Term 2 years 7 months 15 days
Options Exercisable, Number Exercisable (in shares) | shares 49,546
Options Exercisable, Weighted Average Exercise Price Per Share (USD per share) $ 20.36
Options Exercisable, Weighted Average Contractual Term 2 years 7 months 15 days
$19.97 - 21.10 | Minimum  
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]  
Exercise price per share, lower price range limit (USD per share) $ 19.97
$19.97 - 21.10 | Maximum  
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]  
Exercise price per share, upper price range limit (USD per share) $ 21.1
$23.78 - 25.14  
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]  
Options Outstanding, Number Outstanding (in shares) | shares 232,582
Options Outstanding, Weighted Average Exercise Price Per Share (USD per share) $ 24.56
Options Outstanding, Weighted Average Contractual Term 4 years 3 months 29 days
Options Exercisable, Number Exercisable (in shares) | shares 232,582
Options Exercisable, Weighted Average Exercise Price Per Share (USD per share) $ 24.56
Options Exercisable, Weighted Average Contractual Term 4 years 3 months 29 days
$23.78 - 25.14 | Minimum  
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]  
Exercise price per share, lower price range limit (USD per share) $ 23.78
$23.78 - 25.14 | Maximum  
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]  
Exercise price per share, upper price range limit (USD per share) $ 25.14
$29.45 - 32.81  
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]  
Options Outstanding, Number Outstanding (in shares) | shares 537,893
Options Outstanding, Weighted Average Exercise Price Per Share (USD per share) $ 31.68
Options Outstanding, Weighted Average Contractual Term 7 years 7 months 15 days
Options Exercisable, Number Exercisable (in shares) | shares 290,534
Options Exercisable, Weighted Average Exercise Price Per Share (USD per share) $ 30.72
Options Exercisable, Weighted Average Contractual Term 7 years 1 month 26 days
$29.45 - 32.81 | Minimum  
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]  
Exercise price per share, lower price range limit (USD per share) $ 29.45
$29.45 - 32.81 | Maximum  
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]  
Exercise price per share, upper price range limit (USD per share) $ 32.81
$46.95 - 53.72  
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]  
Options Outstanding, Number Outstanding (in shares) | shares 121,602
Options Outstanding, Weighted Average Exercise Price Per Share (USD per share) $ 53.40
Options Outstanding, Weighted Average Contractual Term 9 years 3 months 1 day
Options Exercisable, Number Exercisable (in shares) | shares 38,091
Options Exercisable, Weighted Average Exercise Price Per Share (USD per share) $ 53.72
Options Exercisable, Weighted Average Contractual Term 9 years 2 months 23 days
$46.95 - 53.72 | Minimum  
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]  
Exercise price per share, lower price range limit (USD per share) $ 46.95
$46.95 - 53.72 | Maximum  
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]  
Exercise price per share, upper price range limit (USD per share) $ 53.72