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Accounting for Stock Compensation - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions		3 Months Ended		9 Months Ended
	Apr. 04, 2018	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Allocated share-based compensation expense		$ 6.5	$ 4.5	$ 19.1	$ 14.7
Restricted Stock Units (RSUs)
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation arrangement by share-based payment award, equity instruments other than options, grants in period				149,365
Share-based compensation arrangement by share-based payment award, equity instruments other than options, grants in period, weighted average grant date fair value				$ 76.39
Employee service share-based compensation, nonvested awards, compensation cost not yet recognized		16.7		$ 16.7
Employee service share-based compensation, nonvested awards, compensation cost not yet recognized, period for recognition				1 year 8 months 12 days
Cash Settled RSUs
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation arrangement by share-based payment award, equity instruments other than options, grants in period				98,837
Share-based compensation arrangement by share-based payment award, equity instruments other than options, grants in period, weighted average grant date fair value				$ 76.60
Employee service share-based compensation, nonvested awards, compensation cost not yet recognized		11.8		$ 11.8
Employee service share-based compensation, nonvested awards, compensation cost not yet recognized, period for recognition				1 year 9 months 18 days
Performance Shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation arrangement by share-based payment award, equity instruments other than options, grants in period				47,290
Share-based compensation arrangement by share-based payment award, equity instruments other than options, grants in period, weighted average grant date fair value				$ 82.38
Employee service share-based compensation, nonvested awards, compensation cost not yet recognized		$ 5.1		$ 5.1
Employee service share-based compensation, nonvested awards, compensation cost not yet recognized, period for recognition				1 year 2 months 12 days
Omnibus Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation arrangement by share-based payment award, number of shares grants	1,185,000			330,998
Share-based compensation arrangement by share-based payment award, number of additional awards				0
Share-based compensation arrangement by share-based payment award, number of shares available for grant		905,795		905,795