Revenues from Contracts with Customers - Disaggregation of Revenue (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	Mar. 31, 2022	Mar. 31, 2021
Disaggregation Of Revenue [Line Items]
Revenues	$ 1,583,980	$ 1,551,918	$ 4,560,656	$ 4,480,135
Expertise
Disaggregation Of Revenue [Line Items]
Revenues	716,199	764,419	2,105,554	2,237,378
Technology
Disaggregation Of Revenue [Line Items]
Revenues	867,781	787,499	2,455,102	2,242,757
Prime contractor
Disaggregation Of Revenue [Line Items]
Revenues	1,419,805	1,401,633	4,097,210	4,055,496
Subcontractor
Disaggregation Of Revenue [Line Items]
Revenues	164,175	150,285	463,446	424,639
Department of Defense
Disaggregation Of Revenue [Line Items]
Revenues	1,118,665	1,074,056	3,155,806	3,091,126
Federal civilian agencies
Disaggregation Of Revenue [Line Items]
Revenues	380,837	405,855	1,166,398	1,186,068
Commercial and other
Disaggregation Of Revenue [Line Items]
Revenues	84,478	72,007	238,452	202,941
Cost-plus-fee
Disaggregation Of Revenue [Line Items]
Revenues	889,624	905,774	2,672,695	2,572,967
Fixed-price
Disaggregation Of Revenue [Line Items]
Revenues	503,174	457,099	1,344,169	1,331,734
Time and materials
Disaggregation Of Revenue [Line Items]
Revenues	191,182	189,045	543,792	575,434
Domestic
Disaggregation Of Revenue [Line Items]
Revenues	1,532,880	1,505,037	4,414,852	4,350,284
Domestic | Expertise
Disaggregation Of Revenue [Line Items]
Revenues	697,347	745,440	2,049,180	2,184,449
Domestic | Technology
Disaggregation Of Revenue [Line Items]
Revenues	835,533	759,597	2,365,672	2,165,835
Domestic | Prime contractor
Disaggregation Of Revenue [Line Items]
Revenues	1,373,045	1,358,423	3,964,227	3,935,661
Domestic | Subcontractor
Disaggregation Of Revenue [Line Items]
Revenues	159,835	146,614	450,625	414,623
Domestic | Department of Defense
Disaggregation Of Revenue [Line Items]
Revenues	1,118,665	1,074,056	3,155,806	3,091,126
Domestic | Federal civilian agencies
Disaggregation Of Revenue [Line Items]
Revenues	380,837	405,855	1,166,398	1,186,068
Domestic | Commercial and other
Disaggregation Of Revenue [Line Items]
Revenues	33,378	25,126	92,648	73,090
Domestic | Cost-plus-fee
Disaggregation Of Revenue [Line Items]
Revenues	889,624	905,774	2,672,695	2,572,967
Domestic | Fixed-price
Disaggregation Of Revenue [Line Items]
Revenues	468,116	424,580	1,242,601	1,245,278
Domestic | Time and materials
Disaggregation Of Revenue [Line Items]
Revenues	175,140	174,683	499,556	532,039
International
Disaggregation Of Revenue [Line Items]
Revenues	51,100	46,881	145,804	129,851
International | Expertise
Disaggregation Of Revenue [Line Items]
Revenues	18,852	18,979	56,374	52,929
International | Technology
Disaggregation Of Revenue [Line Items]
Revenues	32,248	27,902	89,430	76,922
International | Prime contractor
Disaggregation Of Revenue [Line Items]
Revenues	46,760	43,210	132,983	119,835
International | Subcontractor
Disaggregation Of Revenue [Line Items]
Revenues	4,340	3,671	12,821	10,016
International | Commercial and other
Disaggregation Of Revenue [Line Items]
Revenues	51,100	46,881	145,804	129,851
International | Fixed-price
Disaggregation Of Revenue [Line Items]
Revenues	35,058	32,519	101,568	86,456
International | Time and materials
Disaggregation Of Revenue [Line Items]
Revenues	$ 16,042	$ 14,362	$ 44,236	$ 43,395