Condensed Consolidated Statements of Operations - USD ($) shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Income Statement [Abstract]
Net sales	$ 492.0	$ 405.3
Operating costs and expenses:
Cost of sales (exclusive of items shown separately below)	426.8	339.4
Selling, general and administrative expense	6.7	13.5
Depreciation and amortization	17.7	16.3
Other expense, net	1.2	1.7
Total operating costs and expenses	452.4	370.9
Operating income	39.6	34.4
Non-operating (income) expense:
Retirement benefits expense	14.4	18.3
Interest income	(1.6)	(0.5)
Interest expense	8.1	7.4
Total non-operating expense, net	20.9	25.2
Income before income taxes	18.7	9.2
Income tax provision	4.7	3.3
Net income	$ 14.0	$ 5.9
Basic
Basic net income per share (in USD per share)	$ 0.19	$ 0.08
Diluted
Diluted net income per share (in USD per share)	$ 0.18	$ 0.08
Weighted average shares of common stock outstanding, basic (in shares)	73.7	72.3
Weighted average shares of common stock outstanding, diluted (in shares)	74.7	72.3