Commitments and Contingencies (Asbestos Liability) (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 ($)	Aug. 21, 2012 USD ($)
Loss Contingencies [Line Items]
Payments for asbestos-related fees and costs, net of insurance recoveries	$ 10,800,000	$ 11,700,000
Estimated payments to current and future claimants	36,000,000,000
Current portion of total estimated liability	$ 66,500,000		$ 66,500,000
Asbestos Commitments and Contingencies
Loss Contingencies [Line Items]
Pending claims | claim	29,407	29,162	29,138	29,056
Payments for asbestos-related fees and costs, net of insurance recoveries	$ 10,800,000	$ 11,700,000	$ 31,100,000
Cumulative claims resolved | claim	142,000
Settlement cost	$ 684,000,000
Average settlement cost per resolved claim			13,900	$ 15,800	$ 11,300
Additional liability				255,000,000
Liability for claims	657,000,000		670,000,000	$ 712,000,000
Percentage Of Asbestos Liability Attributable To Settlement And Defense Costs For Future Claims				85.00%
Current portion of total estimated liability	66,500,000		66,500,000
Aggregate value of policy buyout agreements	82,500,000
Estimated Percentage Of Insurance Which Covers Asbestos Costs				14.00%
Insurance reimbursement asset	84,000,000		87,000,000	$ 98,000,000
Gross Settlement And Defense Incurred Costs	$ 9,100,000	$ 12,600,000	$ 50,900,000
Asbestos Commitments and Contingencies | Ronald Dummitt
Loss Contingencies [Line Items]
Court Judgment						$ 4,900,000
New York | Asbestos Commitments and Contingencies
Loss Contingencies [Line Items]
Pending claims | claim	18,000