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, 2016	$ 266.4	$ 0.6	$ 504.9	$ 469.9	$ (305.2)	$ (403.8)
Balance at Dec. 31, 2016		54,428,233
Balance at Dec. 31, 2016					6,168,907
Cumulative effect impact of ASU 2018-02 / ASU 2016-09 adoption	8.7			8.7
Stock issuance		122,158
Share-based employee compensation	6.8		6.8
Net earnings	121.1			121.1
Separation of Armstrong Flooring, Inc.	0.9		0.9
Other comprehensive income (loss)	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
Balance at Sep. 30, 2017					7,926,654
Balance at Dec. 31, 2017	$ 419.3	$ 0.6	516.8	633.4	$ (385.6)	(345.9)
Balance at Dec. 31, 2017	52,772,139	52,772,139
Balance at Dec. 31, 2017	8,010,597				8,010,597
Cumulative effect impact of ASU 2018-02 / ASU 2016-09 adoption				54.3		(54.3)
Stock issuance		751,279
Share-based employee compensation	$ 25.4		25.4
Net earnings	151.3			151.3
Other comprehensive income (loss)	(9.0)					(9.0)
Deferred accelerated stock repurchase	(30.0)		(30.0)
Acquisition of treasury stock	(226.1)				$ (226.1)
Acquisition of treasury stock, shares		(3,567,733)			3,567,733
Balance at Sep. 30, 2018	$ 330.9	$ 0.6	$ 512.2	$ 839.0	$ (611.7)	$ (409.2)
Balance at Sep. 30, 2018	49,955,685	49,955,685
Balance at Sep. 30, 2018	11,578,330				11,578,330