Accounts Payable And Accrued Expenses (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Schedule Of Accounts Payble And Accrued Expenses [Line Items]
Payables, trade and other	$ 80.7	$ 81.3
Employment costs	12.6	17.6
Current portion of pension and postretirement liabilities	9.6	9.5
Other	12.6	16.7
Total accounts payable and accrued expenses	$ 115.5	136.5
Knauf [Member]
Schedule Of Accounts Payble And Accrued Expenses [Line Items]
Payable to Knauf for purchase price adjustments		$ 11.4