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, 2014	$ 649.1	$ 0.6	$ 1,134.4	$ 271.0	$ (261.4)	$ (495.5)
Balance at Dec. 31, 2014		55,126,153
Balance at Dec. 31, 2014					5,057,382
Stock issuance		228,859
Share-based employee compensation	15.4		15.4
Net earnings	108.0			108.0
Other comprehensive income	10.7					10.7
Balance at Sep. 30, 2015	783.2	$ 0.6	1,149.8	379.0	$ (261.4)	(484.8)
Balance at Sep. 30, 2015		55,355,012
Balance at Sep. 30, 2015					5,057,382
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	55,359,064
Balance at Dec. 31, 2015	5,057,382				5,057,382
Stock issuance		147,488
Share-based employee compensation	$ 13.1		13.1
Net earnings	77.6			77.6
Other comprehensive income	11.3					11.3
Separation of Armstrong Flooring, Inc.	(603.9)		(660.7)			56.8
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	55,319,221
Balance at Sep. 30, 2016	5,244,713				5,244,713