Goodwill And Intangible Assets (Summary Of Intangible Assets) (Detail) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2017	Dec. 31, 2016	Dec. 31, 2015
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Amortization Expense, Remainder of Fiscal Year	$ 7.8
Finite-Lived Intangible Assets, Amortization Expense, Year Two	29.1
Finite-Lived Intangible Assets, Amortization Expense, Year Three	$ 26.4
Weighted Average Amortization Period of Finite Lived Assets (in years)	15 years 10 months 24 days
Gross Asset	$ 577.6	$ 546.7
Accumulated Amortization	292.9	264.5
Net	284.7	282.2
Finite-Lived Intangible Assets, Net	284.7	282.2	$ 317.1
Finite-Lived Intangible Assets, Amortization Expense, Year Four	22.0
Finite-Lived Intangible Assets, Amortization Expense, Year Five	$ 170.9
Intellectual Property Rights
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted Average Amortization Period of Finite Lived Assets (in years)	16 years 6 months
Gross Asset	$ 89.7	86.4
Accumulated Amortization	54.6	52.1
Net	$ 35.1	34.3
Customer Relationships
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted Average Amortization Period of Finite Lived Assets (in years)	15 years 7 months 6 days
Gross Asset	$ 413.5	388.9
Accumulated Amortization	175.2	153.4
Net	$ 238.3	235.5
Drawings
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted Average Amortization Period of Finite Lived Assets (in years)	37 years 10 months 24 days
Gross Asset	$ 11.1	11.1
Accumulated Amortization	10.3	10.3
Net	$ 0.8	0.8
Other Intangible Assets
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted Average Amortization Period of Finite Lived Assets (in years)	12 years 9 months 18 days
Gross Asset	$ 63.3	60.3
Accumulated Amortization	52.8	48.7
Net	$ 10.5	$ 11.6