Condensed Consolidated Statements of Operations - USD ($) shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Income Statement [Abstract]
Net sales	$ 549.8	$ 545.3	$ 1,589.4	$ 1,598.3
Operating costs and expenses:
Cost of sales (exclusive of items shown separately below)	459.3	446.5	1,354.3	1,310.6
Selling, general and administrative expense	5.6	5.2	23.4	27.8
Depreciation and amortization	13.8	13.5	42.0	44.4
Other expense, net
Legal matters	(0.4)	0.0	15.7	0.0
Proxy costs and related litigation	16.3	0.0	28.3	0.0
Other	1.9	8.7	1.5	24.0
Total operating costs and expenses	496.5	473.9	1,465.2	1,406.8
Operating income	53.3	71.4	124.2	191.5
Non-operating:
Retirement benefits expense	0.3	8.5	0.8	25.4
Loss on debt	22.7	0.9	22.7	10.5
Interest income and other	(2.2)	(0.2)	(2.0)	(1.5)
Interest expense	5.1	4.9	13.3	15.1
Total non-operating expense, net	25.9	14.1	34.8	49.5
Income before income taxes	27.4	57.3	89.4	142.0
Income tax provision	13.7	14.8	31.5	36.4
Net income	$ 13.7	$ 42.5	$ 57.9	$ 105.6
Earnings per share of common stock
Basic earnings per share (in dollars per share)	$ 0.17	$ 0.53	$ 0.72	$ 1.33
Diluted earnings per share (in dollars per share)	$ 0.17	$ 0.51	$ 0.70	$ 1.29
Weighted average shares of common stock outstanding, basic (in shares)	80.3	79.9	80.3	79.0
Weighted average shares of common stock outstanding, diluted (in shares)	81.2	82.3	84.3	81.5
Cash dividends paid per share (in dollars per share)	$ 0	$ 0	$ 0	$ 5.00