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Segment Reporting - Revenue by Customer Type (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2025	Mar. 31, 2024
Revenue from External Customer [Line Items]
Revenues	$ 968.3	$ 1,049.0
Federal Government
Revenue from External Customer [Line Items]
Revenues	296.1	317.5
Federal Government | Firm-fixed-price
Revenue from External Customer [Line Items]
Revenues	90.0	89.2
Federal Government | T&M
Revenue from External Customer [Line Items]
Revenues	126.1	131.2
Federal Government | Cost reimbursable
Revenue from External Customer [Line Items]
Revenues	80.0	97.1
Other Federal [Member]
Revenue from External Customer [Line Items]
Revenues	9.1	9.6
Federal Civilian
Revenue from External Customer [Line Items]
Revenues	112.5	120.6
Department of Homeland Security [Member]
Revenue from External Customer [Line Items]
Revenues	45.6	37.2
Department of Defense and Intelligence Agencies
Revenue from External Customer [Line Items]
Revenues	$ 128.9	$ 150.1

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Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).

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