Condensed Consolidated Statements of Cash Flows - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Operating Activities
Net income	$ 70.6	$ 82.8
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	34.6	35.0
Amortization of debt discount and deferred financing costs	4.9	4.6
Stock-based compensation	7.7	15.5
Retirement benefits, net	15.9	10.8
Other, net	0.1	0.4
Changes in assets and liabilities, net of effects from acquisition in 2019:
Accounts receivable, net	32.1	13.8
Contract assets	(63.8)	(11.3)
Other current assets, net	31.6	(0.1)
Recoverable environmental remediation costs	10.3	8.4
Other noncurrent assets, net	7.6	(15.6)
Accounts payable	(47.5)	(10.8)
Contract liabilities	33.4	(59.6)
Other current liabilities	(7.3)	(27.6)
Deferred income taxes	4.1	(19.3)
Reserves for environmental remediation costs	(9.9)	(7.7)
Other noncurrent liabilities and other	3.2	11.9
Net Cash Provided by Operating Activities	127.6	31.2
Investing Activities
Purchases of marketable securities	(25.0)	0.0
Capital expenditures	(16.2)	(6.9)
Net Cash Used in Investing Activities	(41.2)	(6.9)
Financing Activities
Debt repayments	(9.9)	(10.8)
Repurchase of shares for withholding taxes and option costs under equity plans	(8.2)	(6.7)
Proceeds from shares issued under equity plans	3.5	2.2
Purchase of treasury stock	(0.5)	0.0
Net Cash Used in Financing Activities	(15.1)	(15.3)
Net Increase in Cash, Cash Equivalents and Restricted Cash	71.3	9.0
Cash, Cash Equivalents and Restricted Cash at Beginning of Period	935.6	740.3
Cash, Cash Equivalents and Restricted Cash at End of Period	1,006.9	749.3
Supplemental disclosures of cash flow information
Cash paid for interest	10.7	13.7
Cash paid for income taxes	2.4	33.9
Cash refund for income taxes	$ 0.4	$ 1.0