Equity Compensation (Stock Options Outstanding by Exercise Price) (Details) - $ / shares	3 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options Outstanding - Weighted Average Exercise Price (in dollars per share)	$ 19.42	$ 19.44
$ 12.15 – $20.00
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price range, lower limit (in dollars per share)	12.15
Exercise price range, upper limit (in dollars per share)	20.00
$ 20.01 – $25.00
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price range, lower limit (in dollars per share)	20.01
Exercise price range, upper limit (in dollars per share)	25.00
$ 25.01 – $30.00
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price range, lower limit (in dollars per share)	25.01
Exercise price range, upper limit (in dollars per share)	30.00
$ 30.01 – $33.36
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price range, lower limit (in dollars per share)	30.01
Exercise price range, upper limit (in dollars per share)	$ 33.36
Stock Options
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options Outstanding - Number Outstanding at end of period (in shares)	2,380,520
Options Outstanding - Weighted Average Remaining Contractual Life	4 years
Options Outstanding - Weighted Average Exercise Price (in dollars per share)	$ 19.42
Options Exercisable - Number Exercisable At end of period (in shares)	1,780,744
Options Exercisable - Weighted Average Exercise Price (in dollars per share)	$ 21.86
Stock Options | $ 12.15 – $20.00
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options Outstanding - Number Outstanding at end of period (in shares)	970,685
Options Outstanding - Weighted Average Remaining Contractual Life	7 years 8 months
Options Outstanding - Weighted Average Exercise Price (in dollars per share)	$ 12.98
Options Exercisable - Number Exercisable At end of period (in shares)	370,909
Options Exercisable - Weighted Average Exercise Price (in dollars per share)	$ 14.33
Stock Options | $ 20.01 – $25.00
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options Outstanding - Number Outstanding at end of period (in shares)	730,151
Options Outstanding - Weighted Average Remaining Contractual Life	2 years 4 months
Options Outstanding - Weighted Average Exercise Price (in dollars per share)	$ 22.21
Options Exercisable - Number Exercisable At end of period (in shares)	730,151
Options Exercisable - Weighted Average Exercise Price (in dollars per share)	$ 22.21
Stock Options | $ 25.01 – $30.00
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options Outstanding - Number Outstanding at end of period (in shares)	675,188
Options Outstanding - Weighted Average Remaining Contractual Life	1 year 5 months
Options Outstanding - Weighted Average Exercise Price (in dollars per share)	$ 25.56
Options Exercisable - Number Exercisable At end of period (in shares)	675,188
Options Exercisable - Weighted Average Exercise Price (in dollars per share)	$ 25.56
Stock Options | $ 30.01 – $33.36
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options Outstanding - Number Outstanding at end of period (in shares)	4,496
Options Outstanding - Weighted Average Remaining Contractual Life	3 years 1 month
Options Outstanding - Weighted Average Exercise Price (in dollars per share)	$ 33.36
Options Exercisable - Number Exercisable At end of period (in shares)	4,496
Options Exercisable - Weighted Average Exercise Price (in dollars per share)	$ 33.36