Business and Basis of Presentation (Schedule of Prior Year Amounts Recast Affected by Cumulative Adjustment in Accounts Payable and Accrued Expenses) (Details) - Knauf [Member] $ in Millions	Dec. 31, 2018 USD ($)
Error Corrections And Prior Period Adjustments Restatement [Line Items]
Advance receipt of Knauf proceeds	$ 202.4
Contingent liability payable to Knauf for adjustments to cash consideration	35.2
As Reported [Member]
Error Corrections And Prior Period Adjustments Restatement [Line Items]
Advance receipt of Knauf proceeds	$ 237.6