Revenue Recognition - Disaggregation of Revenue (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Disaggregation Of Revenue [Line Items]
Revenue from clients	$ 1,553,048	$ 1,506,875	$ 1,478,525
Time-and-Materials
Disaggregation Of Revenue [Line Items]
Revenue from clients	633,574	732,365	700,980
Fixed-Price
Disaggregation Of Revenue [Line Items]
Revenue from clients	645,351	536,903	566,299
Cost-Based
Disaggregation Of Revenue [Line Items]
Revenue from clients	274,123	237,607	211,246
U.S. Federal Government
Disaggregation Of Revenue [Line Items]
Revenue from clients	735,031	666,968	560,953
U.S. State and Local Government
Disaggregation Of Revenue [Line Items]
Revenue from clients	233,757	219,507	279,833
International Government
Disaggregation Of Revenue [Line Items]
Revenue from clients	136,245	93,581	122,125
Total Government
Disaggregation Of Revenue [Line Items]
Revenue from clients	1,105,033	980,056	962,911
Commercial
Disaggregation Of Revenue [Line Items]
Revenue from clients	448,015	526,819	515,614
Energy, Environmental and Infrastructure
Disaggregation Of Revenue [Line Items]
Revenue from clients	654,488	609,358	663,799
Health, Education and Social Programs
Disaggregation Of Revenue [Line Items]
Revenue from clients	678,047	677,454	567,351
Safety and Security
Disaggregation Of Revenue [Line Items]
Revenue from clients	115,266	120,599	118,279
Consumer and Financial
Disaggregation Of Revenue [Line Items]
Revenue from clients	$ 105,247	$ 99,464	$ 129,096