Long-term Equity-based Compensation - Option and SAR Activity (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Shares Subject to Options at Beginning of Year	1,012,279
Weighted Average Exercise Price Per Share at Beginning of Year	$ 37.45
Grants in Period	576,681
Grants in Period, Weighted Average Exercise Price	$ 60.98
Exercises in Period	(107,536)
Exercises in Period, Weighted Average Exercise Price	$ 36.74
Forfeitures and Expirations in Period	(47,151)
Forfeitures and Expirations in Period, Weighted Average Exercise Price	$ 52.06
Shares Subject to Options at End of Year	1,434,273	1,012,279
Weighted Average Exercise Price Per Share at End of Year	$ 46.48	$ 37.45
Outstanding at End of Year, Weighted Average Remaining Contractual Term	7 years 10 months 9 days
Outstanding at End of Year, Intrinsic Value	$ 28.8
Vested and Expected to Vest, Outstanding at End of Year	1,359,250
Vested and Expected to Vest, Outstanding, Weighted Average Exercise Price	$ 46.22
Vested and Expected to Vest, Outstanding, Weighted Average Remaining Contractual Term	7 years 9 months 25 days
Vested and Expected to Vest, Outstanding, Aggregate Intrinsic Value	$ 27.7
Vested and Expected to Vest, Exercisable at End of Year	586,600
Vested and Expected to Vest, Exercisable at End of Year, Weighted Average Exercise Price	$ 36.18
Vested and Expected to Vest, Exercisable at End of Year, Weighted Average Remaining Contractual Term	6 years 8 months 14 days
Vested and Expected to Vest, Exercisable at End of Year, Aggregate Intrinsic Value	$ 17.7
Weighted-average grant-date fair values (per share)	$ 15.14	$ 8.89	$ 5.17
Cash received from exercises of Tandem Awards	$ 0.9	$ 4.0	$ 3.5
Total tax benefit realized for tax deductions from exercise of Tandem Awards	$ 0.8	$ 1.7	$ 0.7