Consolidated Statements of Cash Flows - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Operating Activities
Net income	$ 143.7	$ 137.7	$ 141.0
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	61.4	65.3	74.5
Amortization of debt discount and deferred financing costs	5.9	9.9	9.4
Stock-based compensation	20.7	31.4	27.3
Retirement benefits, net	12.7	18.1	21.6
Loss on debt repurchased	10.5	0.0	0.0
Other, net	(1.7)	(0.4)	(0.6)
Changes in assets and liabilities, net of effects from acquisition in 2019:
Accounts receivable, net	15.0	36.9	28.8
Contract assets	(65.6)	(64.5)	11.0
Other current assets, net	28.8	9.2	(27.9)
Recoverable for environmental remediation costs	1.5	7.1	16.3
Other noncurrent assets	10.0	0.6	(6.3)
Accounts payable	24.3	(36.8)	20.3
Contract liabilities	(40.7)	144.9	(10.3)
Other current liabilities	7.6	(4.4)	(72.5)
Deferred income taxes	(18.0)	37.9	(5.7)
Reserves for environmental remediation costs	(4.2)	(8.6)	(18.7)
Other noncurrent liabilities and other	(12.3)	(20.5)	53.0
Net Cash Provided by Operating Activities	199.6	363.8	261.2
Investing Activities
Capital expenditures	(37.3)	(54.6)	(42.9)
Purchases of marketable securities	(1.9)	(31.7)	0.0
Sale of marketable securities	0.0	25.0	0.0
Other	0.0	0.3	1.1
Net Cash Used in Investing Activities	(39.2)	(61.0)	(41.8)
Financing Activities
Dividend payments	(428.8)	0.0	0.0
Debt principal payments	(182.6)	(21.7)	(20.8)
Proceeds from shares issued under equity plans	7.7	7.5	5.2
Repurchase of shares for withholding taxes and option costs under employee equity plans	(5.8)	(20.0)	(8.5)
Purchase of treasury stock	0.0	(51.7)	0.0
Net Cash Used in Financing Activities	(609.5)	(85.9)	(24.1)
Net (Decrease) Increase in Cash, Cash Equivalents and Restricted Cash	(449.1)	216.9	195.3
Cash, Cash Equivalents and Restricted Cash at Beginning of Year	1,152.5	935.6	740.3
Cash, Cash Equivalents and Restricted Cash at End of Year	703.4	1,152.5	935.6
Supplemental disclosures of cash flow information
Cash paid for interest	14.0	19.7	26.3
Cash paid for income taxes	39.7	56.0	63.8
Cash refund for income taxes	$ 1.6	$ 13.3	$ 2.0