Accounts Payable And Accrued Expenses (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Schedule Of Accounts Payble And Accrued Expenses [Line Items]
Payables, trade and other	$ 62.4	$ 79.4
Current portion of lease liabilities	5.2	5.2
Employment costs	4.4	16.5
Current portion of pension and postretirement liabilities	10.5	10.5
Other	12.4	10.0
Total accounts payable and accrued expenses	127.0	148.7
Knauf [Member]
Schedule Of Accounts Payble And Accrued Expenses [Line Items]
Payable to Knauf for purchase price adjustments	6.2	1.2
WAVE [Member]
Schedule Of Accounts Payble And Accrued Expenses [Line Items]
Payable to WAVE for receipt of Knauf proceeds	$ 25.9	$ 25.9