Acquisitions (Narrative) (Details) - USD ($) $ in Millions								12 Months Ended
	Dec. 16, 2020	Aug. 24, 2020	Jul. 27, 2020	Nov. 25, 2019	Mar. 04, 2019	Aug. 16, 2018	May 31, 2018	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Business Acquisition [Line Items]
Business acquisition, goodwill								$ 160.7	$ 53.0
Net sales								936.9	1,038.1	$ 975.3
Net (loss) earnings								(99.1)	$ 214.5	$ 185.9
Arktura [Member]
Business Acquisition [Line Items]
Payments to acquire business	$ 90.6
Business acquisition, cash acquired	0.8
Business acquisition, total fair value of liabilities assumed, less tangible assets acquired	4.1
Business acquisition, total fair value of intangible assets acquired	36.2
Business acquisition, goodwill	$ 51.1
Amortizable intangible asset weighted average useful life	4 years 3 months 18 days
Arktura [Member] | Seller [Member]
Business Acquisition [Line Items]
Business acquisition additional cash payments	$ 24.0
Business acquisition cash payment period	5 years
Business acquisition agreement employment period	5 years
Arktura [Member] | Seller [Member] | Restricted Stock [Member]
Business Acquisition [Line Items]
Business acquisition, stock issued or issuable	$ 6.0
Business acquisition stock issued vesting period	5 years
Arktura [Member] | Key Employee [Member]
Business Acquisition [Line Items]
Business acquisition agreement employment period	3 years
Arktura [Member] | Key Employee [Member] | Restricted Stock [Member]
Business Acquisition [Line Items]
Business acquisition, stock issued or issuable	$ 1.4
Business acquisition stock issued vesting period	3 years
Arktura [Member] | TradeNames [Member]
Business Acquisition [Line Items]
Business acquisition, total fair value of intangible assets acquired	$ 14.5
Arktura [Member] | Customer Relationships [Member]
Business Acquisition [Line Items]
Business acquisition, total fair value of intangible assets acquired	$ 3.3
Amortizable intangible asset weighted average useful life	1 year
Arktura [Member] | Software Development [Member]
Business Acquisition [Line Items]
Business acquisition, total fair value of intangible assets acquired	$ 9.1
Amortizable intangible asset weighted average useful life	7 years
Arktura [Member] | Backlog [Member]
Business Acquisition [Line Items]
Business acquisition, total fair value of intangible assets acquired	$ 5.9
Amortizable intangible asset weighted average useful life	1 year
Arktura [Member] | Noncompete Agreements [Member]
Business Acquisition [Line Items]
Business acquisition, total fair value of intangible assets acquired	$ 2.8
Amortizable intangible asset weighted average useful life	5 years
Arktura [Member] | Patents [Member]
Business Acquisition [Line Items]
Business acquisition, total fair value of intangible assets acquired	$ 0.6
Amortizable intangible asset weighted average useful life	17 years
Moz Designs, Inc. [Member]
Business Acquisition [Line Items]
Payments to acquire business		$ 4.2
Business acquisition, total fair value of liabilities assumed, less tangible assets acquired		0.4
Business acquisition, total fair value of intangible assets acquired		2.7
Business acquisition, goodwill		4.6
Business combination contingent consideration maximum earnout payable		4.7
Business combination, consideration transferred estimated fair value		2.7
Business combination, consideration transferred		6.9
Moz Designs, Inc. [Member] | TradeNames [Member]
Business Acquisition [Line Items]
Business acquisition, total fair value of intangible assets acquired		1.5
Moz Designs, Inc. [Member] | Customer Relationships [Member]
Business Acquisition [Line Items]
Business acquisition, total fair value of intangible assets acquired		0.6
Moz Designs, Inc. [Member] | Backlog [Member]
Business Acquisition [Line Items]
Business acquisition, total fair value of intangible assets acquired		$ 0.6
Turf [Member]
Business Acquisition [Line Items]
Payments to acquire business			$ 70.0
Business acquisition, total fair value of intangible assets acquired			27.9
Business acquisition, goodwill			$ 51.4
Amortizable intangible asset weighted average useful life			8 years 3 months 18 days
Business combination contingent consideration maximum earnout payable			$ 48.0
Business combination, consideration transferred estimated fair value			14.1
Business combination, consideration transferred			84.1
Business acquisition, total fair value of tangible assets acquired, less liabilities assumed			4.8
Turf [Member] | Patents [Member]
Business Acquisition [Line Items]
Business acquisition, total fair value of intangible assets acquired			$ 5.8
Amortizable intangible asset weighted average useful life			20 years
Turf [Member] | Noncompete Agreements [Member]
Business Acquisition [Line Items]
Business acquisition, total fair value of intangible assets acquired			$ 3.3
Amortizable intangible asset weighted average useful life			5 years
Turf [Member] | Target Payout [Member]
Business Acquisition [Line Items]
Additional cash considerations			$ 24.0
Annual growth rate of contingent consideration			23.00%
Turf [Member] | Over Target Payout [Member]
Business Acquisition [Line Items]
Annual growth rate of contingent consideration			38.00%
Turf [Member] | Over Target Payout [Member] | Maximum [Member]
Business Acquisition [Line Items]
Additional cash considerations			$ 24.0
Turf [Member] | TradeNames [Member]
Business Acquisition [Line Items]
Business acquisition, total fair value of intangible assets acquired			9.6
Turf [Member] | Customer Relationships [Member]
Business Acquisition [Line Items]
Business acquisition, total fair value of intangible assets acquired			$ 7.7
Amortizable intangible asset weighted average useful life			2 years
MRK Industries, Inc. [Member]
Business Acquisition [Line Items]
Business acquisition, goodwill				$ 10.4
Business combination, consideration transferred				13.3
Business acquisition, total fair value of tangible assets acquired, less liabilities assumed				$ 2.9
Architectural Components Group, Inc. [Member]
Business Acquisition [Line Items]
Business acquisition, total fair value of intangible assets acquired					$ 12.0
Business acquisition, goodwill					23.6
Business combination, consideration transferred					42.9
Business acquisition, total fair value of tangible assets acquired, less liabilities assumed					7.3
Architectural Components Group, Inc. [Member] | TradeNames [Member]
Business Acquisition [Line Items]
Business acquisition, total fair value of intangible assets acquired					2.8
Architectural Components Group, Inc. [Member] | Customer Relationships [Member]
Business Acquisition [Line Items]
Business acquisition, total fair value of intangible assets acquired					$ 7.4
Steel Ceilings, Inc. [Member]
Business Acquisition [Line Items]
Business acquisition, goodwill						$ 3.2
Business combination, consideration transferred						12.3
Business acquisition, total fair value of tangible assets acquired, less liabilities assumed						4.4
Proceed from sale of acquired product						2.0
Steel Ceilings, Inc. [Member] | TradeNames [Member]
Business Acquisition [Line Items]
Business acquisition, total fair value of intangible assets acquired						1.3
Steel Ceilings, Inc. [Member] | Customer Relationships [Member]
Business Acquisition [Line Items]
Business acquisition, total fair value of intangible assets acquired						$ 1.4
Plasterform, Inc. [Member]
Business Acquisition [Line Items]
Business acquisition, total fair value of intangible assets acquired							$ 4.8
Business acquisition, goodwill							4.9
Business combination, consideration transferred							11.9
Business acquisition, total fair value of tangible assets acquired, less liabilities assumed							$ 2.2
Arktura Moz and Turf [Member]
Business Acquisition [Line Items]
Net sales								18.2
Net (loss) earnings								$ 0.4