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Revenue Recognition - Disaggregation of Revenue (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024
Disaggregation Of Revenue [Line Items]
Revenue from clients	$ 465,405	$ 516,998	$ 1,429,178	$ 1,523,463
Time-and-Materials
Disaggregation Of Revenue [Line Items]
Revenue from clients	205,683	220,332	621,422	644,125
Fixed-Price
Disaggregation Of Revenue [Line Items]
Revenue from clients	226,781	236,770	703,321	696,910
Cost-Based
Disaggregation Of Revenue [Line Items]
Revenue from clients	32,941	59,896	104,435	182,428
U.S. Federal Government
Disaggregation Of Revenue [Line Items]
Revenue from clients	198,042	281,970	641,240	830,070
U.S. State and Local Government
Disaggregation Of Revenue [Line Items]
Revenue from clients	81,698	78,686	244,491	240,801
International Government
Disaggregation Of Revenue [Line Items]
Revenue from clients	29,021	26,817	85,369	80,760
Total Government
Disaggregation Of Revenue [Line Items]
Revenue from clients	308,761	387,473	971,100	1,151,631
Commercial
Disaggregation Of Revenue [Line Items]
Revenue from clients	$ 156,644	$ 129,525	$ 458,078	$ 371,832
Customer Concentration Risk | Revenue from Contract with Customer
Disaggregation Of Revenue [Line Items]
Revenue from clients, Percent	100.00%	100.00%	100.00%	100.00%
Customer Concentration Risk | Revenue from Contract with Customer | Time-and-Materials
Disaggregation Of Revenue [Line Items]
Revenue from clients, Percent	44.00%	43.00%	43.00%	42.00%
Customer Concentration Risk | Revenue from Contract with Customer | Fixed-Price
Disaggregation Of Revenue [Line Items]
Revenue from clients, Percent	49.00%	46.00%	49.00%	46.00%
Customer Concentration Risk | Revenue from Contract with Customer | Cost-Based
Disaggregation Of Revenue [Line Items]
Revenue from clients, Percent	7.00%	11.00%	8.00%	12.00%
Customer Concentration Risk | Revenue from Contract with Customer | U.S. Federal Government
Disaggregation Of Revenue [Line Items]
Revenue from clients, Percent	43.00%	55.00%	45.00%	55.00%
Customer Concentration Risk | Revenue from Contract with Customer | U.S. State and Local Government
Disaggregation Of Revenue [Line Items]
Revenue from clients, Percent	17.00%	15.00%	17.00%	16.00%
Customer Concentration Risk | Revenue from Contract with Customer | International Government
Disaggregation Of Revenue [Line Items]
Revenue from clients, Percent	6.00%	5.00%	6.00%	5.00%
Customer Concentration Risk | Revenue from Contract with Customer | Total Government
Disaggregation Of Revenue [Line Items]
Revenue from clients, Percent	66.00%	75.00%	68.00%	76.00%
Customer Concentration Risk | Revenue from Contract with Customer | Commercial
Disaggregation Of Revenue [Line Items]
Revenue from clients, Percent	34.00%	25.00%	32.00%	24.00%
Energy, Environment, Infrastructure, and Disaster Recovery
Disaggregation Of Revenue [Line Items]
Revenue from clients	$ 246,239	$ 237,056	$ 732,182	$ 694,940
Energy, Environment, Infrastructure, and Disaster Recovery | Customer Concentration Risk | Revenue from Contract with Customer
Disaggregation Of Revenue [Line Items]
Revenue from clients, Percent	53.00%	46.00%	51.00%	46.00%
Health and Social Programs
Disaggregation Of Revenue [Line Items]
Revenue from clients	$ 151,976	$ 196,772	$ 480,489	$ 583,415
Health and Social Programs | Customer Concentration Risk | Revenue from Contract with Customer
Disaggregation Of Revenue [Line Items]
Revenue from clients, Percent	33.00%	38.00%	34.00%	38.00%
Security and Other Civilian & Commercial
Disaggregation Of Revenue [Line Items]
Revenue from clients	$ 67,190	$ 83,170	$ 216,507	$ 245,108
Security and Other Civilian & Commercial | Customer Concentration Risk | Revenue from Contract with Customer
Disaggregation Of Revenue [Line Items]
Revenue from clients, Percent	14.00%	16.00%	15.00%	16.00%

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- Definition

For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

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