Share-Based Compensation Share-Based Compensation Price Ranges (Details)	12 Months Ended
	Dec. 31, 2017 $ / shares shares
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Outstanding Stock Options (in shares) | shares	2,287,399
Outstanding Stock Options Weighted Average Remaining Contractual Term (in years)	3 years 10 months 6 days
Outstanding Stock Options Weighted Average Exercise Price (in dollars per share)	$ 39.67
Exercisable Stock Options (in shares) | shares	1,650,386
Exercisable Stock Options, Weighted Average Exercise Price (in dollars per share)	$ 26.33
Exercise Price Range 18.00 to 20.34 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Outstanding Stock Options (in shares) | shares	885,493
Outstanding Stock Options Weighted Average Remaining Contractual Term (in years)	1 year 4 months 10 days
Outstanding Stock Options Weighted Average Exercise Price (in dollars per share)	$ 19.54
Exercisable Stock Options (in shares) | shares	885,493
Exercisable Stock Options, Weighted Average Exercise Price (in dollars per share)	$ 19.54
Exercise price range per share, lower range (in dollars per share)	18.00
Exercise price range per share, upper range (in dollars per share)	$ 20.34
Exercise Price Range 20.35 to 45.61 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Outstanding Stock Options (in shares) | shares	811,756
Outstanding Stock Options Weighted Average Remaining Contractual Term (in years)	3 years 10 months 28 days
Outstanding Stock Options Weighted Average Exercise Price (in dollars per share)	$ 33.75
Exercisable Stock Options (in shares) | shares	695,031
Exercisable Stock Options, Weighted Average Exercise Price (in dollars per share)	$ 31.76
Exercise price range per share, lower range (in dollars per share)	20.35
Exercise price range per share, upper range (in dollars per share)	$ 45.61
Exercise Price Range 45.62 to 117.04 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Outstanding Stock Options (in shares) | shares	590,150
Outstanding Stock Options Weighted Average Remaining Contractual Term (in years)	7 years 6 months 4 days
Outstanding Stock Options Weighted Average Exercise Price (in dollars per share)	$ 78.02
Exercisable Stock Options (in shares) | shares	69,862
Exercisable Stock Options, Weighted Average Exercise Price (in dollars per share)	$ 58.30
Exercise price range per share, lower range (in dollars per share)	45.62
Exercise price range per share, upper range (in dollars per share)	$ 117.04