Statement of Consolidated Cash Flows $ in Millions	12 Months Ended
	Dec. 31, 2019 USD ($)		Dec. 31, 2018 USD ($)		Dec. 31, 2017 USD ($)
Cash flows from operating activities:
Net income	$ 62.0		$ 91.7		$ 45.4
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation of property, plant and equipment	46.3		42.1		38.3
Amortization of definite-lived intangible assets	2.8		1.8		1.4
Amortization of debt discount and debt issuance costs	1.2		1.0		1.2
Deferred income taxes	21.1		36.7		89.0
Non-cash equity compensation	9.8		10.3		13.3
Non-cash asset impairment charges	26.1		1.4		19.2
Loss on extinguishment of debt	20.3		0.0		0.0
Gain on disposition of property, plant and equipment	0.0		(0.2)		(0.5)
Gain on disposition of short-term investments	(0.9)		(2.9)		(2.3)
Non-cash defined benefit net periodic postretirement benefit cost	7.0		6.6		4.8
Other non-cash changes in assets and liabilities	(8.6)		(21.9)		15.5
Changes in operating assets and liabilities:
Trade and other receivables	20.2		(22.3)		(30.9)
Contract assets	(0.3)		(0.7)		0.0
Inventories	37.5		(45.0)		(6.3)
Prepaid expenses and other current assets	(1.7)		(0.4)		(1.7)
Accounts payable	(24.5)		29.2		13.0
Accrued liabilities	(7.5)		(2.6)		(4.7)
Annual variable cash contributions to VEBAs	(2.1)		(15.7)		(20.0)
Long-term assets and liabilities, net	5.8		(4.1)		(2.2)
Net cash provided by operating activities	232.3	[1]	150.2	[1]	141.5	[1]
Cash flows from investing activities:
Capital expenditures	(60.2)		(74.1)		(75.5)
Purchase of short-term investments	(132.2)		(135.2)		(247.5)
Purchase of equity securities	(0.7)		(0.9)		0.0
Proceeds from disposition of short-term investments	91.1		283.9		296.9
Cash payment for acquisition of Imperial Machine & Tool Co., net of cash received	0.0		(43.2)		0.0
Proceeds from disposal of property, plant and equipment	0.2		0.6		0.6
Net cash (used in) provided by investing activities	(101.8)	[1]	31.1	[1]	(25.5)	[1]
Cash flows from financing activities:
Repayment of principal and redemption premium of 5.875% Senior Notes	(391.5)		0.0		0.0
Issuance of 4.625% Senior Notes	500.0		0.0		0.0
Cash paid for debt issuance costs	8.8		0.0		0.0
Repayment of finance lease	(1.4)		(0.7)		(0.4)
Cancellation of shares to cover employees' tax withholdings upon vesting of non-vested shares	(6.2)		(6.9)		(4.5)
Repurchase of common stock	(44.2)		(60.7)		(79.5)
Cash dividends and dividend equivalents paid	(39.4)		(37.7)		(35.0)
Net cash provided by (used in) financing activities	8.5	[1]	(106.0)	[1]	(119.4)	[1]
Net increase (decrease) in cash, cash equivalents and restricted cash during the period	139.0		75.3		(3.4)
Cash, cash equivalents and restricted cash at end of period	264.3		125.6		51.1
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	$ 278.6		$ 139.6		$ 64.3

[1] See Note 15 for supplemental disclosure on non-cash transactions.