Statements of Consolidated Income (Unaudited) - USD ($) shares in Thousands, $ in Millions	3 Months Ended			9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Mar. 31, 2016	Sep. 30, 2017	Sep. 30, 2016
Income Statement [Abstract]
Net sales	$ 332.8	$ 320.6		$ 1,044.4	$ 998.7
Cost of products sold:
Cost of products sold, excluding depreciation and amortization and other items	267.2	254.7		822.7	767.1
Lower of cost or market inventory write-down	0.0	0.0	$ 4.9	0.0	4.9
Unrealized gain on derivative instruments	(10.8)	(2.0)		(14.0)	(16.9)
Depreciation and amortization	10.2	9.0		29.3	26.7
Selling, general, administrative, research and development	24.7	25.6		74.7	79.2
Net periodic postretirement benefit cost relating to Salaried VEBA	1.2	0.8		3.4	2.5
Loss (gain) on removal of Union VEBA net assets	0.5	0.0		(0.8)	(0.1)
Total selling, general, administrative, research and development	26.4	26.4		77.3	81.6
Goodwill impairment	0.0	0.0		18.4	0.0
Other operating charges, net	0.0	2.7		0.0	2.8
Total costs and expenses	293.0	290.8		933.7	866.2
Operating income	39.8	29.8		110.7	132.5
Other (expense) income:
Interest expense	(5.3)	(5.5)		(16.4)	(14.7)
Other (expense) income, net	1.5	0.0		3.1	(10.4)
Income before income taxes	36.0	24.3		97.4	107.4
Income tax provision	(16.1)	(9.4)		(36.8)	(40.2)
Net income	$ 19.9	$ 14.9		$ 60.6	$ 67.2
Net income per common share:
Basic (in dollars per share)	$ 1.18	$ 0.84		$ 3.55	$ 3.76
Diluted (in dollars per share)	$ 1.16	$ 0.82		$ 3.49	$ 3.70
Weighted-average number of common shares outstanding (in thousands):
Basic (shares)	16,834	17,841		17,072	17,858
Diluted (shares)	17,160	18,175		17,363	18,181
Cash dividends declared (in dollars per share)	$ 0.50	$ 0.45		$ 1.50	$ 1.35