Commitments and Contingencies (Schedule Of Activity Related To Asbestos Claim) (Detail)	3 Months Ended		12 Months Ended
	Mar. 31, 2021 USD ($) claim	Mar. 31, 2020 USD ($) claim	Dec. 31, 2020 USD ($) claim	Dec. 31, 2019 USD ($) claim	Dec. 31, 2018 USD ($)
Loss Contingencies [Line Items]
Current asbestos liability	$ 66,500,000		$ 66,500,000
Payments for asbestos-related fees and costs, net of insurance recoveries	10,800,000	$ 11,700,000
Asbestos Commitments and Contingencies
Loss Contingencies [Line Items]
Asbestos Settlement Cost Per Resolved Claim			13,900	$ 15,800	$ 11,300
Current asbestos liability	66,500,000		$ 66,500,000
Aggregate Value Of Policy Buy Out Agreements	$ 82,500,000
Beginning claims | claim	29,138	29,056	29,056
New claims | claim	733	681	2,620
Settlements | claim	(160)	(165)	(885)
Dismissals | claim	(304)	(410)	(1,653)
Ending claims | claim	29,407	29,162	29,138	29,056
Gross Settlement And Defense Incurred Costs	$ 9,100,000	$ 12,600,000	$ 50,900,000
Payments for asbestos-related fees and costs, net of insurance recoveries	10,800,000	$ 11,700,000	$ 31,100,000
Cumulative Asbestos Settlement Cost Per Resolved Claim	$ 4,800
New York | Asbestos Commitments and Contingencies
Loss Contingencies [Line Items]
Ending claims | claim	18,000
us-gaap_LossContingencyPendingClaimsNumber (nonmalignancy) | claim	16,000