Business and Basis of Presentation (Narrative) (Details) $ in Millions				6 Months Ended		12 Months Ended
	Jul. 27, 2020 USD ($)	Nov. 25, 2019 Facility	Mar. 04, 2019 Facility	Jun. 30, 2020 USD ($)	Jun. 30, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2020 USD ($)
Business And Basis Of Presentation [Line Items]
Amount remitted for portion of remaining proceeds				$ 20.0
Cash considerations					$ 43.1
EMEA and Pacific Rim Business [Member]
Business And Basis Of Presentation [Line Items]
Consideration received in connection with sale of businesses						$ 330.0
Knauf [Member]
Business And Basis Of Presentation [Line Items]
Discontinued operation, working capital adjustment to cash consideration payable				6.2
Contingent accrued liabilities				$ 0.0
Knauf [Member] | Forecast [Member]
Business And Basis Of Presentation [Line Items]
Contingent accrued liabilities							$ 11.0
WAVE [Member]
Business And Basis Of Presentation [Line Items]
Equity interest percentage				50.00%
Amount remitted for portion of remaining proceeds				$ 20.0
Accounts payable and accrued expenses related to payable to equity method investee				$ 5.9
MRK Industries, Inc. [Member]
Business And Basis Of Presentation [Line Items]
Number of manufacturing facility | Facility		1
Architectural Components Group, Inc. [Member]
Business And Basis Of Presentation [Line Items]
Number of manufacturing facility | Facility			1
Turf [Member] | Subsequent Event [Member]
Business And Basis Of Presentation [Line Items]
Cash considerations	$ 70.0
Additional cash considerations	24.0
Revenues	$ 20.0
Annual growth rate of contingent consideration	23.00%
Turf [Member] | Subsequent Event [Member] | Maximum [Member]
Business And Basis Of Presentation [Line Items]
Additional cash considerations	$ 24.0
Annual growth rate of contingent consideration	38.00%