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Segment Reporting - Revenue by Customer Type (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024
Revenue from External Customer [Line Items]
Revenues	$ 1,020.6	$ 1,034.7	$ 1,988.9	$ 2,083.7
Federal Government
Revenue from External Customer [Line Items]
Revenues	312.5	309.0	608.6	626.5
Federal Government | Firm-fixed-price
Revenue from External Customer [Line Items]
Revenues	86.0	92.0	176.0	181.2
Federal Government | T&M
Revenue from External Customer [Line Items]
Revenues	128.1	136.2	254.2	267.4
Federal Government | Cost reimbursable
Revenue from External Customer [Line Items]
Revenues	98.4	80.8	178.4	177.9
Other Federal [Member]
Revenue from External Customer [Line Items]
Revenues	31.2	31.1	62.3	61.6
Federal Civilian
Revenue from External Customer [Line Items]
Revenues	57.8	69.1	119.8	135.6
Department of Homeland Security [Member]
Revenue from External Customer [Line Items]
Revenues	87.3	67.2	161.4	137.6
Department of Defense and Intelligence Agencies
Revenue from External Customer [Line Items]
Revenues	$ 136.2	$ 141.6	$ 265.1	$ 291.7

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