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		112,176
Share-based employee compensation	3.8		3.8
Net earnings	71.7			71.7
Separation of Armstrong Flooring, Inc.	0.9		0.9
Other comprehensive income (loss)	16.7					16.7
Acquisition of treasury stock	(70.9)				$ (70.9)
Acquisition of treasury stock, shares		(1,659,452)			1,659,452
Balance at Jun. 30, 2017	297.3	$ 0.6	509.6	550.3	$ (376.1)	(387.1)
Balance at Jun. 30, 2017		52,880,957
Balance at Jun. 30, 2017					7,828,359
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		651,726
Share-based employee compensation	$ 18.9		18.9
Net earnings	75.1			75.1
Other comprehensive income (loss)	(4.2)					(4.2)
Acquisition of treasury stock	(105.0)	$ (105.0)			$ (105.0)
Acquisition of treasury stock, shares		(1,785,816)			1,785,816
Balance at Jun. 30, 2018	$ 404.1	$ 0.6	$ 535.7	$ 762.8	$ (490.6)	$ (404.4)
Balance at Jun. 30, 2018	51,638,049	51,638,049
Balance at Jun. 30, 2018	9,796,413				9,796,413