Condensed Consolidated Statements of Operations - USD ($) shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Income Statement [Abstract]
Net sales	$ 476.1	$ 491.7
Operating costs and expenses:
Cost of sales (exclusive of items shown separately below)	394.9	397.6
Selling, general and administrative expense	9.1	12.2
Depreciation and amortization	17.2	17.5
Other (income) expense, net	(2.2)	1.1
Total operating costs and expenses	419.0	428.4
Operating income	57.1	63.3
Non-operating:
Retirement benefits expense	9.2	6.5
Interest income	(3.2)	(4.0)
Interest expense	8.4	9.0
Total non-operating expense, net	14.4	11.5
Income before income taxes	42.7	51.8
Income tax provision	11.3	13.1
Net income	$ 31.4	$ 38.7
Earnings per share of common stock
Basic earnings per share (in dollars per share)	$ 0.40	$ 0.49
Diluted earnings per share (in dollars per share)	$ 0.37	$ 0.47
Weighted average shares of common stock outstanding, basic (in shares)	77.5	77.1
Weighted average shares of common stock outstanding, diluted (in shares)	83.1	80.6