Condensed Consolidated Statements Of Shareholders' Equity - USD ($) $ in Millions	Total	Common Stock [Member]	Additional Paid-In Capital [Member]	Retained Earnings [Member]	Treasury Stock [Member]	Accumulated Other Comprehensive (Loss) [Member]
Balance at Dec. 31, 2015	$ 768.8	$ 0.6	$ 1,151.8	$ 365.2	$ (261.4)	$ (487.4)
Balance at Dec. 31, 2015		55,359,064
Balance at Dec. 31, 2015					5,057,382
Stock issuance		147,488
Share-based employee compensation	13.1		13.1
Net earnings (loss)	77.6			77.6
Separation of Armstrong Flooring, Inc.	(603.9)		(660.7)			56.8
Other comprehensive income	11.3					11.3
Acquisition of treasury stock	(7.8)				$ (7.8)
Acquisition of treasury stock, shares		(187,331)			187,331
Balance at Sep. 30, 2016	259.1	$ 0.6	504.2	442.8	$ (269.2)	(419.3)
Balance at Sep. 30, 2016		55,319,221
Balance at Sep. 30, 2016					5,244,713
Balance at Dec. 31, 2016	$ 266.4	$ 0.6	504.9	469.9	$ (305.2)	(403.8)
Balance at Dec. 31, 2016	54,428,233	54,428,233
Balance at Dec. 31, 2016	6,168,907				6,168,907
Cumulative effect impact of ASU 2016-09 adoption	$ 8.7			8.7
Stock issuance		122,158
Share-based employee compensation	6.8		6.8
Net earnings (loss)	121.1			121.1
Separation of Armstrong Flooring, Inc.	0.9		0.9
Other comprehensive income	37.7					37.7
Acquisition of treasury stock	(75.4)				$ (75.4)
Acquisition of treasury stock, shares		(1,757,747)			1,757,747
Balance at Sep. 30, 2017	$ 366.2	$ 0.6	$ 512.6	$ 599.7	$ (380.6)	$ (366.1)
Balance at Sep. 30, 2017	52,792,644	52,792,644
Balance at Sep. 30, 2017	7,926,654				7,926,654