Condensed Consolidated Statements of Stockholders' Equity (Unaudited) - USD ($) $ in Millions	Total	Common Stock	Capital in Excess of Par Value	Retained Earnings	Treasury Stock	Accumulated Other Comprehensive Loss
Beginning Balance at Dec. 31, 2018	$ 530.1	$ 66.4	$ 217.0	$ 432.5	$ (88.5)	$ (97.3)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	50.3			50.3
Total other comprehensive income (loss)	1.1					1.1	[1]
Cash dividends declared	(9.6)			(9.6)
Stock-based payments:
Stock-based compensation	3.5		3.5
Stock option exercises and other	0.1	0.2	0.9		(1.0)
Performance share unit transactions	(0.9)	0.1	(0.1)		(0.9)
Stock repurchase program	(1.0)				(1.0)
Ending Balance at Jun. 30, 2019	580.1	66.7	221.3	479.7	(91.4)	(96.2)
Beginning Balance at Mar. 31, 2019	548.4	66.5	218.4	451.7	(90.6)	(97.6)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	32.8			32.8
Total other comprehensive income (loss)	1.4					1.4	[1]
Cash dividends declared	(4.8)			(4.8)
Stock-based payments:
Stock-based compensation	2.1		2.1
Stock option exercises and other	0.2	0.2	0.8		(0.8)
Ending Balance at Jun. 30, 2019	580.1	66.7	221.3	479.7	(91.4)	(96.2)
Stock-based payments:
Impact of adoption of ASU 2016-02 | Accounting Standards Update 2016-02	6.5			6.5
Beginning Balance at Dec. 31, 2019	641.6	66.9	228.6	528.2	(93.0)	(89.1)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	44.8			44.8
Total other comprehensive income (loss)	(5.6)					(5.6)	[1]
Cash dividends declared	(9.7)			(9.7)
Stock-based payments:
Stock-based compensation	3.9		3.9
Stock option exercises and other	(3.2)	0.4	2.4		(6.0)
Performance share unit transactions	(2.9)	0.2	(0.2)		(2.9)
Stock repurchase program	(13.5)				(13.5)
Ending Balance at Jun. 30, 2020	655.4	67.5	234.7	563.3	(115.4)	(94.7)
Beginning Balance at Mar. 31, 2020	636.2	67.2	230.1	546.8	(111.4)	(96.5)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	21.4			21.4
Total other comprehensive income (loss)	1.8					1.8	[1]
Cash dividends declared	(4.9)			(4.9)
Stock-based payments:
Stock-based compensation	2.9		2.9
Stock option exercises and other	(2.0)	0.3	1.7		(4.0)
Ending Balance at Jun. 30, 2020	$ 655.4	$ 67.5	$ 234.7	$ 563.3	$ (115.4)	$ (94.7)

[1] Amounts in parentheses indicate losses.