Condensed Consolidated Statements of Cash Flows - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Operating Activities
Net income	$ 102.3	$ 115.7
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	49.7	53.4
Amortization of debt discount and deferred financing costs	7.4	7.0
Stock-based compensation	13.2	24.5
Retirement benefits, net	18.9	16.2
Other, net	0.2	0.3
Changes in assets and liabilities, net of effects from acquisition in 2019:
Accounts receivable, net	(69.9)	(29.7)
Contract assets	(49.2)	(2.0)
Other current assets, net	7.3	(22.8)
Recoverable environmental remediation costs	6.0	10.5
Other noncurrent assets, net	6.9	(21.5)
Accounts payable	(33.6)	7.8
Contract liabilities	81.1	(4.5)
Other current liabilities	(12.0)	(45.1)
Deferred income taxes	4.2	(19.3)
Reserves for environmental remediation costs	(5.1)	(9.7)
Other noncurrent liabilities and other	11.2	15.6
Net Cash Provided by Operating Activities	138.6	96.4
Investing Activities
Purchases of marketable securities	(26.5)	0.0
Sales of marketable securities	25.0	0.0
Capital expenditures	(31.0)	(16.3)
Net Cash Used in Investing Activities	(32.5)	(16.3)
Financing Activities
Debt repayments	(14.7)	(15.9)
Repurchase of shares for withholding taxes and option costs under equity plans	(8.8)	(7.5)
Proceeds from shares issued under equity plans	7.1	5.1
Purchase of treasury stock	(12.3)	0.0
Net Cash Used in Financing Activities	(28.7)	(18.3)
Net Increase in Cash, Cash Equivalents and Restricted Cash	77.4	61.8
Cash, Cash Equivalents and Restricted Cash at Beginning of Period	935.6	740.3
Cash, Cash Equivalents and Restricted Cash at End of Period	1,013.0	802.1
Supplemental disclosures of cash flow information
Cash paid for interest	13.5	18.6
Cash paid for income taxes	35.9	48.9
Cash refund for income taxes	$ 0.4	$ 1.0