Discontinued Operations (Summary Of Cash Flow Data Related To Discontinued Operations) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Non-cash investing activities - capital expenditures, consisting of of unpaid capital expenditure liabilities at year end	$ 5,300	$ 3,500	$ 7,700
Tile Coatings [Member] | Discontinued Operations [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Depreciation		11,264	10,778
Amortization of intangible assets		3,192	3,219
Capital expenditures	(4,713)	(9,965)	(5,830)
Non-cash operating activities - goodwill impairment		42,515
Non-cash operating activities - restructuring	1,080	127
Non-cash investing activities - capital expenditures, consisting of of unpaid capital expenditure liabilities at year end	$ 1,493	$ 1,087	$ 5,926