Goodwill And Intangible Assets (Summary Of Intangible Assets) (Detail) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2021	Dec. 31, 2020	Dec. 31, 2019
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted Average Amortization Period of Finite Lived Assets (in years)	17 years 9 months 18 days
Intangible Assets, Gross (Excluding Goodwill)	$ 895.8	$ 908.2
Finite-Lived Intangible Assets, Accumulated Amortization	417.1	389.1
Intangible assets, net	478.7	519.1	$ 503.7
Remainder of 2021	11.1
2022	42.7
2023	42.6
2024	41.7
2025 and after	$ 269.8
Intellectual Property Rights
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted Average Amortization Period of Finite Lived Assets (in years)	15 years 1 month 6 days
Intangible Assets, Gross (Excluding Goodwill)	$ 132.3	133.2
Finite-Lived Intangible Assets, Accumulated Amortization	54.1	53.4
Intangible assets, net	$ 78.2	79.8
Customer Relationships
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted Average Amortization Period of Finite Lived Assets (in years)	18 years 3 months 18 days
Intangible Assets, Gross (Excluding Goodwill)	$ 614.3	623.7
Finite-Lived Intangible Assets, Accumulated Amortization	263.4	241.9
Intangible assets, net	$ 350.9	381.8
Drawings
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted Average Amortization Period of Finite Lived Assets (in years)	40 years
Intangible Assets, Gross (Excluding Goodwill)	$ 11.1	11.1
Finite-Lived Intangible Assets, Accumulated Amortization	10.6	10.5
Intangible assets, net	$ 0.5	0.6
Other Intangible Assets
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted Average Amortization Period of Finite Lived Assets (in years)	11 years 8 months 12 days
Intangible Assets, Gross (Excluding Goodwill)	$ 138.1	140.2
Finite-Lived Intangible Assets, Accumulated Amortization	89.0	83.3
Intangible assets, net	$ 49.1	$ 56.9