Commitments and Contingencies (Schedule Of Activity Related To Asbestos Claim) (Detail)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2020 USD ($) claim	Sep. 30, 2019 USD ($) claim	Sep. 30, 2020 USD ($) claim	Sep. 30, 2019 USD ($) claim	Dec. 31, 2019 USD ($) claim	Dec. 31, 2018 USD ($) claim	Dec. 31, 2017 USD ($)	Apr. 22, 2016 USD ($)	Jul. 02, 2015 USD ($)	Sep. 17, 2013 USD ($)	Feb. 25, 2013	Feb. 23, 2011 USD ($)	Mar. 23, 2010 USD ($)
Loss Contingencies [Line Items]
Current asbestos liability	$ 65,000,000.0		$ 65,000,000.0		$ 65,000,000.0
Payments for asbestos-related fees and costs, net of insurance recoveries			23,700,000	$ 29,000,000.0
Asbestos Commitments and Contingencies
Loss Contingencies [Line Items]
Asbestos Settlement Cost Per Resolved Claim					$ 15,800	$ 11,300	$ 7,800
Current asbestos liability	65,000,000		65,000,000
Aggregate Value Of Policy Buy Out Agreements	$ 82,500,000		$ 82,500,000
Court Judgment		$ 54,200,000		$ 54,200,000
Beginning claims | claim			29,056	29,089	29,089
New claims | claim	707	746	1,965	2,190	2,848
Settlements | claim	(152)	(177)	(581)	(763)	(983)
Dismissals | claim	(174)	(591)	(1,132)	(1,687)	(1,898)
Ending claims | claim	29,308	28,829	29,308	28,829	29,056	29,089
Gross Settlement And Defense Incurred Costs	$ 6,300,000	$ 13,900,000	$ 30,200,000	$ 54,200,000	$ 66,200,000
Payments for asbestos-related fees and costs, net of insurance recoveries	$ 4,600,000	$ 11,000,000.0	$ 23,700,000	$ 28,900,000	$ 41,500,000
New York | Asbestos Commitments and Contingencies
Loss Contingencies [Line Items]
Ending claims | claim	18,000		18,000
Texas | Asbestos Commitments and Contingencies
Loss Contingencies [Line Items]
Ending claims | claim	100		100
Mississippi | Asbestos Commitments and Contingencies
Loss Contingencies [Line Items]
Ending claims | claim	300		300
OHIO | Asbestos Commitments and Contingencies
Loss Contingencies [Line Items]
Ending claims | claim	200		200
James Nelson | Asbestos Commitments and Contingencies
Loss Contingencies [Line Items]
Jury Verdict													$ 14,500,000
Court Judgment Against All Parties Held Responsible												$ 4,000,000.0
Additional Judgment Interest												$ 10,000.00
Share Of Responsibility Of Verdict													9.09%
Thomas Amato | Asbestos Commitments and Contingencies
Loss Contingencies [Line Items]
Share Of Responsibility Of Verdict											10.00%
Frank Vincinguerra | Asbestos Commitments and Contingencies
Loss Contingencies [Line Items]
Share Of Responsibility Of Verdict											20.00%
Richard DeLisle | Asbestos Commitments and Contingencies
Loss Contingencies [Line Items]
Jury Verdict										$ 8,000,000
Court Judgment										$ 1,300,000
Share Of Responsibility Of Verdict										16.00%
James Poage | Asbestos Commitments and Contingencies
Loss Contingencies [Line Items]
Court Judgment									$ 10,800,000
compensatory_damages									1,500,000
Additional Damages									$ 10,000,000
George Coulbourn | Asbestos Commitments and Contingencies
Loss Contingencies [Line Items]
Court Judgment								$ 6,800,000
Share Of Responsibility Of Verdict								20.00%
Jury Verdict Total								$ 9,000,000
Additional Damages								$ 5,000,000