Revenue Recognition - Disaggregation of Revenue (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Disaggregation Of Revenue [Line Items]
Revenue from clients	$ 494,436	$ 483,282
Time-and-Materials
Disaggregation Of Revenue [Line Items]
Revenue from clients	206,160	201,203
Fixed-Price
Disaggregation Of Revenue [Line Items]
Revenue from clients	224,725	218,735
Cost-Based
Disaggregation Of Revenue [Line Items]
Revenue from clients	63,551	63,344
U.S. Federal Government
Disaggregation Of Revenue [Line Items]
Revenue from clients	274,177	267,742
U.S. State and Local Government
Disaggregation Of Revenue [Line Items]
Revenue from clients	76,905	75,242
International Government
Disaggregation Of Revenue [Line Items]
Revenue from clients	25,276	20,684
Total Government
Disaggregation Of Revenue [Line Items]
Revenue from clients	376,358	363,668
Commercial
Disaggregation Of Revenue [Line Items]
Revenue from clients	$ 118,078	$ 119,614
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	42.00%	42.00%
Customer Concentration Risk | Revenue from Contract with Customer | Fixed-Price
Disaggregation Of Revenue [Line Items]
Revenue from clients, Percent	45.00%	45.00%
Customer Concentration Risk | Revenue from Contract with Customer | Cost-Based
Disaggregation Of Revenue [Line Items]
Revenue from clients, Percent	13.00%	13.00%
Customer Concentration Risk | Revenue from Contract with Customer | U.S. Federal Government
Disaggregation Of Revenue [Line Items]
Revenue from clients, Percent	55.00%	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%	4.00%
Customer Concentration Risk | Revenue from Contract with Customer | Total Government
Disaggregation Of Revenue [Line Items]
Revenue from clients, Percent	76.00%	75.00%
Customer Concentration Risk | Revenue from Contract with Customer | Commercial
Disaggregation Of Revenue [Line Items]
Revenue from clients, Percent	24.00%	25.00%
Energy, Environment, Infrastructure, and Disaster Recovery
Disaggregation Of Revenue [Line Items]
Revenue from clients	$ 224,689	$ 187,218
Energy, Environment, Infrastructure, and Disaster Recovery | Customer Concentration Risk | Revenue from Contract with Customer
Disaggregation Of Revenue [Line Items]
Revenue from clients, Percent	45.00%	39.00%
Health and Social Programs
Disaggregation Of Revenue [Line Items]
Revenue from clients	$ 190,148	$ 202,782
Health and Social Programs | Customer Concentration Risk | Revenue from Contract with Customer
Disaggregation Of Revenue [Line Items]
Revenue from clients, Percent	39.00%	42.00%
Security and Other Civilian & Commercial
Disaggregation Of Revenue [Line Items]
Revenue from clients	$ 79,599	$ 93,282
Security and Other Civilian & Commercial | Customer Concentration Risk | Revenue from Contract with Customer
Disaggregation Of Revenue [Line Items]
Revenue from clients, Percent	16.00%	19.00%