Statements of Consolidated Income - USD ($) shares in Thousands, $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Income Statement [Abstract]
Net sales	$ 355.3	$ 343.2
Cost of products sold:
Cost of products sold, excluding depreciation and amortization and other items	277.8	262.0
Lower of cost or market inventory write-down	0.0	4.9
Unrealized gain on derivative instruments	(15.1)	(4.0)
Depreciation and amortization	9.6	8.7
Selling, general, administrative, research and development	23.7	26.1
Net periodic postretirement benefit cost relating to Salaried VEBA	1.1	0.8
Gain on removal of Union VEBA net assets – Note 5	(1.3)	(0.1)
Total selling, general, administrative, research and development	23.5	26.8
Total costs and expenses	295.8	298.4
Operating income	59.5	44.8
Other (expense) income:
Interest expense	(5.6)	(3.7)
Other income, net	0.6	0.3
Income before income taxes	54.5	41.4
Income tax provision	(18.5)	(15.1)
Net income	$ 36.0	$ 26.3
Net income per common share:
Basic (in dollars per share)	$ 2.07	$ 1.47
Diluted (in dollars per share)	$ 2.04	$ 1.44
Weighted-average number of common shares outstanding (in thousands):
Basic (shares)	17,385	17,864
Diluted (shares)	17,603	18,200
Cash dividends declared (in dollars per share)	$ 0.50	$ 0.45