Supplemental Balance Sheet Information - Schedule of Supplemental Balance Sheet Information (Details) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
Trade Receivables, Net
Allowance for doubtful receivables	$ (0.6)	$ (0.5)
Trade receivables, net	351.5	297.2
Inventories
Finished products	98.8	98.0
Work-in-process	217.0	242.5
Raw materials	158.3	174.0
Operating supplies	14.5	10.9
Inventories	488.6	525.4
Property, Plant and Equipment, Net
Land and improvements	38.4	28.4
Buildings and leasehold improvements	199.6	185.5
Machinery and equipment	1,255.4	1,232.7
Construction in progress	203.1	141.3
Property, plant and equipment, gross	1,696.5	1,587.9
Accumulated depreciation and amortization	(639.0)	(574.9)
Assets held for sale		0.2
Property, plant and equipment, net	1,057.5	1,013.2
Other Accrued Liabilities
Uncleared cash disbursements	23.3	13.6
Accrued income taxes and other taxes payable	10.7	8.9
Accrued interest	10.3	9.9
Short-term environmental accrual - Note 7	1.1	1.1
Short-term operating lease liabilities	8.2	9.1
Short-term finance lease liabilities	2.1	2.1
Other - Note 5	17.4	23.7
Other accrued liabilities	73.1	68.4
Long-Term Liabilities
Workers' compensation accrual	32.2	30.9
Long-term environmental accrual - Note 7	16.7	16.6
Other long-term liabilities	36.6	27.2
Long-term liabilities	85.5	74.7
Billed
Trade Receivables, Net
Billed trade receivables	$ 352.1	$ 297.7