CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Millions	12 Months Ended
	Dec. 27, 2020	Dec. 29, 2019	Dec. 30, 2018
Operating activities:
Net income (loss)	$ 79.4	$ 12.6	$ (3.5)
Income (loss) from discontinued operations	(0.9)	1.7	(7.6)
Income from continuing operations	80.3	10.9	4.1
Adjustments to reconcile income from continuing operations to net cash provided by (used in) operating activities from continuing operations:
Depreciation and amortization	24.6	23.4	17.9
Deferred income taxes	(78.2)	(4.9)	(0.4)
Amortization of lease right-of-use assets	9.4	11.7	0.0
Stock-based compensation	21.0	11.0	7.2
Amortization of deferred financing costs	1.0	1.0	1.0
Provision for doubtful accounts	0.0	(0.2)	1.8
Changes in assets and liabilities, net of acquisitions:
Accounts receivable	(3.7)	(11.6)	8.2
Unbilled receivables	3.6	(1.6)	(35.9)
Inventoried costs	(5.3)	(4.6)	2.0
Prepaid expenses	(2.1)	0.3	2.2
Other assets	(8.7)	(0.9)	1.2
Operating lease liabilities	(10.2)	(6.3)	0.0
Accounts payable	(2.4)	4.8	12.2
Accrued expenses	1.0	(6.4)	(1.7)
Accrued compensation	8.5	1.7	3.3
Accrued interest	(0.1)	(0.1)	(0.1)
Billings in excess of costs and earnings on uncompleted contracts	(5.0)	(2.4)	(6.9)
Income tax receivable and payable	(1.1)	1.8	0.2
Other liabilities	12.1	1.3	1.8
Net cash provided by operating activities from continuing operations	44.7	28.9	18.1
Investing activities:
Cash paid for acquisitions, net of cash acquired	(51.5)	(17.7)	(2.9)
Proceeds from sale of assets	0.1	0.3	66.0
Capital expenditures	(35.9)	(26.3)	(22.6)
Net cash provided by (used in) investing activities from continuing operations	(87.3)	(43.7)	40.5
Financing activities:
Proceeds from the issuance of long-term debt	5.1	0.0	0.0
Proceeds (expenses) from the issuance of common stock	240.4	0.0	(1.1)
Repayment under credit facility and debt	(0.6)	0.0	(0.8)
Debt issuance costs	0.0	0.0	(0.1)
Payments under finance leases	(0.6)	(0.5)	0.0
Proceeds from exercise of restricted stock units, employee stock options, and employee stock purchase plan	3.4	4.0	3.7
Net cash provided by financing activities from continuing operations	247.7	3.5	1.7
Net cash flows of continuing operations	205.1	(11.3)	60.3
Net operating cash flows of discontinued operations	1.9	1.1	(7.7)
Effect of exchange rate changes on cash, cash equivalents and restricted cash	1.9	(0.2)	(0.5)
Net increase (decrease) in cash, cash equivalents and restricted cash	208.9	(10.4)	52.1
Cash, cash equivalents and restricted cash at beginning of year	172.6	183.0	130.9
Cash, cash equivalents and restricted cash at end of year	381.5	172.6	183.0
Supplemental disclosure of cash flow information:
Cash paid during the year for interest	19.9	19.9	20.5
Net cash paid during the year for income taxes	2.5	0.6	1.5
Non-cash financing and investing activities:
Capital expenditures included in accounts payable and accrued expenses	$ 2.9	$ 1.4	$ 1.3