STATEMENTS OF CONSOLIDATED CASH FLOWS - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Cash flows from operating activities:
Net income (loss)	$ 47.2	$ (29.6)	$ (18.5)
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities:
Depreciation of property, plant and equipment	103.3	97.6	82.5
Amortization of definite-lived intangible assets	5.3	9.3	9.0
Amortization of debt premium and debt issuance costs	2.2	2.3	2.1
Deferred income taxes	7.5	(12.0)	(11.4)
Non-cash equity compensation	16.1	14.3	12.9
Non-cash asset impairment charges		23.7
Loss on extinguishment of debt			35.9
Gain on disposition of property, plant and equipment	(13.8)	(6.0)	(0.5)
Gain on reimbursement on certain machinery and equipment - Note 13		(6.0)
Non-cash defined benefit net periodic postretirement benefit cost	13.4	13.1	9.4
Changes in operating assets and liabilities, net of effects of acquisition:
Trade and other receivables	33.1	15.0	(90.3)
Contract assets	0.1	4.6	(27.1)
Inventories	48.2	(120.8)	(43.5)
Prepaid expenses and other current assets	(2.8)	(1.5)	(0.9)
Accounts payable	(43.0)	(61.2)	112.5
Accrued liabilities	6.6	4.4	17.3
Annual variable cash contributions to Salaried VEBA			(1.7)
Long-term assets and liabilities, net	(11.5)	(10.3)	(8.3)
Net cash provided by (used in) operating activities	211.9	(63.1)	79.4
Cash flows from investing activities:
Capital expenditures	(143.2)	(142.5)	(58.0)
Purchase of equity securities	(0.3)	(0.3)	(0.4)
Proceeds from sale of equity securities	0.1
Cash payment for acquisition of Warrick, net of cash received – Note 4			(609.2)
Proceeds from reimbursement on certain machinery and equipment - Note 13		6.0
Proceeds from disposition of property, plant and equipment	15.2	11.0	1.8
Net cash used in investing activities	(128.2)	(125.8)	(665.8)
Cash flows from financing activities:
Borrowings under the Revolving Credit Facility	215.1
Repayment of borrowings under the Revolving Credit Facility	(215.1)
Cash paid for debt issuance costs		(1.8)	(8.6)
Repayment of finance lease	(2.1)	(2.1)	(2.1)
Cancellation of shares to cover tax withholdings upon common shares issued	(1.8)	(2.8)	(2.6)
Cash dividends and dividend equivalents paid	(50.4)	(50.1)	(46.7)
Net cash (used in) provided by financing activities	(54.3)	(56.8)	109.1
Net increase (decrease) in cash, cash equivalents and restricted cash during the period	29.4	(245.7)	(477.3)
Cash, cash equivalents and restricted cash at beginning of period	71.3	317.0	794.3
Cash, cash equivalents and restricted cash at end of period	$ 100.7	$ 71.3	317.0
6.50% Senior Notes
Cash flows from financing activities:
Repayment of principal and redemption premium of Senior Notes			(380.9)
4.50% Senior Notes
Cash flows from financing activities:
Issuance of Senior Notes			$ 550.0