Accounts Payable And Accrued Expenses (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Schedule Of Accounts Payble And Accrued Expenses [Line Items]
Payables, trade and other	$ 94.3	$ 81.3
Employment costs	26.4	17.6
Current portion of pension and postretirement liabilities	9.6	9.5
Acquisition-related contingent consideration	5.3	0.0
Other	21.2	16.7
Total accounts payable and accrued expenses	156.8	136.5
Knauf [Member]
Schedule Of Accounts Payble And Accrued Expenses [Line Items]
Payable to Knauf for purchase price adjustments	$ 0.0	$ 11.4