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		78,402
Share-based employee compensation	1.1		1.1
Net earnings	30.4			30.4
Separation of Armstrong Flooring, Inc.	0.9		0.9
Other comprehensive income	13.7					13.7
Acquisition of treasury stock	(50.0)				$ (50.0)
Acquisition of treasury stock, shares		(1,190,021)			1,190,021
Balance at Mar. 31, 2017	271.2	$ 0.6	506.9	509.0	$ (355.2)	(390.1)
Balance at Mar. 31, 2017		53,316,614
Balance at Mar. 31, 2017					7,358,928
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		591,584
Share-based employee compensation	$ 15.2		15.2
Net earnings	27.8			27.8
Other comprehensive income	11.5					11.5
Acquisition of treasury stock	(70.0)	$ (70.0)			$ (70.0)
Acquisition of treasury stock, shares		(1,165,247)			1,165,247
Balance at Mar. 31, 2018	$ 403.8	$ 0.6	$ 532.0	$ 715.5	$ (455.6)	$ (388.7)
Balance at Mar. 31, 2018	52,198,476	52,198,476
Balance at Mar. 31, 2018	9,175,844				9,175,844