Segment Reporting - Disaggregated Revenue (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Revenue from External Customer [Line Items]
Revenues	$ 3,980.4	$ 4,099.7	$ 4,450.6
Federal Government Business
Revenue from External Customer [Line Items]
Revenues	1,190.2	1,231.0	1,276.2
Federal Government Business | FFP
Revenue from External Customer [Line Items]
Revenues	348.7	367.7	386.7
Federal Government Business | T&M
Revenue from External Customer [Line Items]
Revenues	474.6	522.0	504.9
Federal Government Business | Cost reimbursable
Revenue from External Customer [Line Items]
Revenues	$ 366.9	$ 341.3	$ 384.6