Revenue Recognition - Disaggregation of Revenue (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Disaggregation Of Revenue [Line Items]
Revenue from clients	$ 1,963,238	$ 1,779,964	$ 1,553,048
Time-and-Materials
Disaggregation Of Revenue [Line Items]
Revenue from clients	812,430	713,693	633,135
Fixed-Price
Disaggregation Of Revenue [Line Items]
Revenue from clients	885,465	802,568	645,809
Cost-Based
Disaggregation Of Revenue [Line Items]
Revenue from clients	265,343	263,703	274,104
U.S. Federal Government
Disaggregation Of Revenue [Line Items]
Revenue from clients	1,084,043	980,746	735,032
U.S. State and Local Government
Disaggregation Of Revenue [Line Items]
Revenue from clients	308,134	259,764	235,416
International Government
Disaggregation Of Revenue [Line Items]
Revenue from clients	103,399	103,609	139,229
Total Government
Disaggregation Of Revenue [Line Items]
Revenue from clients	1,495,576	1,344,119	1,109,677
Commercial
Disaggregation Of Revenue [Line Items]
Revenue from clients	467,662	435,845	443,371
Energy, Environment, Infrastructure, and Disaster Recovery
Disaggregation Of Revenue [Line Items]
Revenue from clients	806,482	714,628	693,572
Health and Social Programs
Disaggregation Of Revenue [Line Items]
Revenue from clients	814,454	704,465	563,590
Security and Other Civilian & Commercial
Disaggregation Of Revenue [Line Items]
Revenue from clients	$ 342,302	$ 360,871	$ 295,886