STATEMENTS OF CONSOLIDATED CASH FLOWS - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2025		Dec. 31, 2024		Dec. 31, 2023
Cash flows from operating activities:
Net (loss) income	[2]	$ 112.5	[1]	$ 65.7	[3]	$ 67.8	[3]
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation of property, plant and equipment	[2]	118.0		111.9	[4]	103.3	[4]
Amortization of definite-lived intangible assets	[2]	4.5		4.5	[4]	5.3	[4]
Amortization and write-off of debt issuance costs	[2]	4.5		2.3	[4]	2.2	[4]
Deferred income taxes	[2]	33.1		12.6	[4]	13.6	[4]
Non-cash equity compensation	[2]	18.5		14.4	[4]	16.1	[4]
Non-cash asset impairment charges	[2],[5]	2.0		3.6	[4]
Gain on disposition of property, plant and equipment and asset write-offs, net	[2]	(7.1)		(3.3)	[4]	(13.8)	[4]
Bad debt expense	[2]	0.4		0.3	[4]
Non-cash postretirement and postemployment defined benefit plan cost		9.5		9.0		13.4
Changes in operating assets and liabilities:
Trade and other receivables	[2]	(81.9)		(4.5)	[4]	33.1	[4]
Contract assets	[2]	10.0		(14.9)	[4]	0.1	[4]
Inventories	[2]	(125.3)		(50.4)	[4]	21.5	[4]
Prepaid expenses and other current assets	[2]	1.0		(9.6)	[4]	(2.8)	[4]
Accounts payable	[2]	15.1		14.1	[4]	(43.0)	[4]
Accrued liabilities	[2]	13.4		9.9	[4]	6.6	[4]
Annual variable cash contributions to Salaried VEBA	[2]	(0.7)		(1.1)	[4]
Long-term assets and liabilities, net	[2]	(16.1)		2.6	[4]	(11.5)	[4]
Net cash provided by operating activities	[2]	111.4		167.1	[4]	211.9	[4]
Cash flows from investing activities:
Capital expenditures	[2]	(136.9)		(180.8)	[4]	(143.2)	[4]
Purchase of equity securities	[2]	(0.4)		(0.1)	[4]	(0.3)	[4]
Proceeds from sale of equity securities	[2]	6.4		0.3	[4]	0.1	[4]
Proceeds from disposition of property, plant and equipment	[2]	53.1		6.0	[4]	15.2	[4]
Net cash used in investing activities	[2]	(77.8)		(174.6)	[4]	(128.2)	[4]
Cash flows from financing activities:
Borrowings under the Revolving Credit Facility		653.3				215.1	[2],[4]
Repayment of borrowings under the Revolving Credit Facility		(631.0)				(215.1)	[2],[4]
Issuance of 5.875% Senior Notes	[2]	500.0
Repayment of principal of 4.625% Senior Notes	[2]	(500.0)
Cash paid for debt issuance costs	[2]	(10.1)
Repayment of finance lease	[2]	(2.5)		(2.5)	[4]	(2.1)	[4]
Cancellation of shares to cover tax withholdings upon common shares issued	[2]	(3.0)		(2.1)	[4]	(1.8)	[4]
Cash dividends and dividend equivalents paid	[2]	(51.3)		(50.7)	[4]	(50.4)	[4]
Net cash used in financing activities	[2]	(44.6)		(55.3)	[4]	(54.3)	[4]
Net (decrease) increase in cash, cash equivalents and restricted cash during the period		(11.0)		(62.8)	[4]	29.4	[4]
Cash, cash equivalents and restricted cash at beginning of period	[4]	37.9		100.7		71.3
Cash, cash equivalents and restricted cash at end of period		$ 26.9		$ 37.9	[4]	$ 100.7	[4]

[1] Adjusted to reflect the retrospective change in inventory valuation methodology from LIFO to WAC. See Note 18 for further discussion.

[2] See Note 16 for supplemental disclosure of cash flow information.

[3] Adjusted to reflect the retrospective change in inventory valuation methodology from LIFO to WAC. See Note 18 for further discussion.

[4] Adjusted to reflect the retrospective change in inventory valuation methodology from LIFO to WAC. See Note 18 for further discussion.

[5] Non-cash asset impairment charges for the year ended December 31, 2025 are comprised of a $2.0 million write-down of certain replacement parts. Non-cash asset impairment charges for the year ended December 31, 2024 are comprised of: (i) a $3.2 million inventory write-down related to certain alloying metals and (ii) a $0.4 million impairment charge on land held for sale.