Long-term Equity-based Compensation - Option and SAR Activity (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Shares Subject to Options at Beginning of Year	1,306,123
Weighted Average Exercise Price Per Share at Beginning of Year	$ 36.35
Grants in Period	444,339
Grants in Period, Weighted Average Exercise Price	$ 43.72
Exercises in Period	(377,811)
Exercises in Period, Weighted Average Exercise Price	$ 35.60
Forfeitures and Expirations in Period	(360,372)
Forfeitures and Expirations in Period, Weighted Average Exercise Price	$ 43.14
Shares Subject to Options at End of Year	1,012,279	1,306,123
Weighted Average Exercise Price Per Share at End of Year	$ 37.45	$ 36.35
Outstanding at End of Year, Weighted Average Remaining Contractual Term	7 years 10 months 5 days
Outstanding at End of Year, Intrinsic Value	$ 31.8
Vested and Expected to Vest, Outstanding at End of Year	959,899
Vested and Expected to Vest, Outstanding, Weighted Average Exercise Price	$ 37.40
Vested and Expected to Vest, Outstanding, Weighted Average Remaining Contractual Term	7 years 9 months 22 days
Vested and Expected to Vest, Outstanding, Aggregate Intrinsic Value	$ 30.2
Vested and Expected to Vest, Exercisable at End of Year	470,946
Vested and Expected to Vest, Exercisable at End of Year, Weighted Average Exercise Price	$ 35.49
Vested and Expected to Vest, Exercisable at End of Year, Weighted Average Remaining Contractual Term	6 years 11 months 2 days
Vested and Expected to Vest, Exercisable at End of Year, Aggregate Intrinsic Value	$ 15.7
Weighted-average grant-date fair values (per share)	$ 8.89	$ 5.17	$ 7.85
Cash received from exercises of Tandem Awards	$ 4.0	$ 3.5	$ 3.9
Total tax benefit realized for tax deductions from exercise of Tandem Awards	$ 1.7	$ 0.7	$ 1.6