Revenue Recognition - Disaggregation of Revenue (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2025	Mar. 31, 2024
Disaggregation Of Revenue [Line Items]
Revenue from clients	$ 487,618	$ 494,436
Time-and-Materials
Disaggregation Of Revenue [Line Items]
Revenue from clients	209,046	206,153
Fixed-Price
Disaggregation Of Revenue [Line Items]
Revenue from clients	238,072	224,796
Cost-Based
Disaggregation Of Revenue [Line Items]
Revenue from clients	40,500	63,487
U.S. Federal Government
Disaggregation Of Revenue [Line Items]
Revenue from clients	239,620	274,195
U.S. State and Local Government
Disaggregation Of Revenue [Line Items]
Revenue from clients	76,865	76,953
International Government
Disaggregation Of Revenue [Line Items]
Revenue from clients	27,075	25,263
Total Government
Disaggregation Of Revenue [Line Items]
Revenue from clients	343,560	376,411
Commercial
Disaggregation Of Revenue [Line Items]
Revenue from clients	$ 144,058	$ 118,025
Customer Concentration Risk | Revenue from Contract with Customer
Disaggregation Of Revenue [Line Items]
Revenue from clients, Percent	100.00%	100.00%
Customer Concentration Risk | Revenue from Contract with Customer | Time-and-Materials
Disaggregation Of Revenue [Line Items]
Revenue from clients, Percent	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%	45.00%
Customer Concentration Risk | Revenue from Contract with Customer | Cost-Based
Disaggregation Of Revenue [Line Items]
Revenue from clients, Percent	8.00%	13.00%
Customer Concentration Risk | Revenue from Contract with Customer | U.S. Federal Government
Disaggregation Of Revenue [Line Items]
Revenue from clients, Percent	49.00%	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	16.00%	16.00%
Customer Concentration Risk | Revenue from Contract with Customer | International Government
Disaggregation Of Revenue [Line Items]
Revenue from clients, Percent	5.00%	5.00%
Customer Concentration Risk | Revenue from Contract with Customer | Total Government
Disaggregation Of Revenue [Line Items]
Revenue from clients, Percent	70.00%	76.00%
Customer Concentration Risk | Revenue from Contract with Customer | Commercial
Disaggregation Of Revenue [Line Items]
Revenue from clients, Percent	30.00%	24.00%
Energy, Environment, Infrastructure, and Disaster Recovery
Disaggregation Of Revenue [Line Items]
Revenue from clients	$ 238,570	$ 224,692
Energy, Environment, Infrastructure, and Disaster Recovery | Customer Concentration Risk | Revenue from Contract with Customer
Disaggregation Of Revenue [Line Items]
Revenue from clients, Percent	49.00%	45.00%
Health and Social Programs
Disaggregation Of Revenue [Line Items]
Revenue from clients	$ 169,023	$ 190,892
Health and Social Programs | Customer Concentration Risk | Revenue from Contract with Customer
Disaggregation Of Revenue [Line Items]
Revenue from clients, Percent	35.00%	39.00%
Security and Other Civilian & Commercial
Disaggregation Of Revenue [Line Items]
Revenue from clients	$ 80,025	$ 78,852
Security and Other Civilian & Commercial | Customer Concentration Risk | Revenue from Contract with Customer
Disaggregation Of Revenue [Line Items]
Revenue from clients, Percent	16.00%	16.00%