Revenues and Contract Balances - Disaggregation of Revenues (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Mar. 31, 2023	Mar. 31, 2022	Mar. 31, 2023	Mar. 31, 2022
Disaggregation Of Revenue [Line Items]
Revenues	$ 1,744,270	$ 1,583,980	$ 4,999,445	$ 4,560,656
Expertise
Disaggregation Of Revenue [Line Items]
Revenues	812,300	716,199	2,288,123	2,105,554
Technology
Disaggregation Of Revenue [Line Items]
Revenues	931,970	867,781	2,711,322	2,455,102
Prime contractor
Disaggregation Of Revenue [Line Items]
Revenues	1,556,733	1,419,805	4,467,882	4,097,210
Subcontractor
Disaggregation Of Revenue [Line Items]
Revenues	187,537	164,175	531,563	463,446
Department of Defense
Disaggregation Of Revenue [Line Items]
Revenues	1,298,700	1,118,665	3,554,080	3,155,806
Federal Civilian agencies
Disaggregation Of Revenue [Line Items]
Revenues	355,612	380,837	1,179,467	1,166,398
Commercial and other
Disaggregation Of Revenue [Line Items]
Revenues	89,958	84,478	265,898	238,452
Cost-plus-fee
Disaggregation Of Revenue [Line Items]
Revenues	1,008,688	889,624	2,896,778	2,672,695
Fixed-price
Disaggregation Of Revenue [Line Items]
Revenues	529,786	503,174	1,520,915	1,344,169
Time-and-materials
Disaggregation Of Revenue [Line Items]
Revenues	205,796	191,182	581,752	543,792
Domestic
Disaggregation Of Revenue [Line Items]
Revenues	1,694,479	1,532,880	4,858,549	4,414,852
Domestic | Expertise
Disaggregation Of Revenue [Line Items]
Revenues	793,993	697,347	2,237,146	2,049,180
Domestic | Technology
Disaggregation Of Revenue [Line Items]
Revenues	900,486	835,533	2,621,403	2,365,672
Domestic | Prime contractor
Disaggregation Of Revenue [Line Items]
Revenues	1,511,758	1,373,045	4,339,579	3,964,227
Domestic | Subcontractor
Disaggregation Of Revenue [Line Items]
Revenues	182,721	159,835	518,970	450,625
Domestic | Department of Defense
Disaggregation Of Revenue [Line Items]
Revenues	1,298,700	1,118,665	3,554,080	3,155,806
Domestic | Federal Civilian agencies
Disaggregation Of Revenue [Line Items]
Revenues	355,612	380,837	1,179,467	1,166,398
Domestic | Commercial and other
Disaggregation Of Revenue [Line Items]
Revenues	40,167	33,378	125,002	92,648
Domestic | Cost-plus-fee
Disaggregation Of Revenue [Line Items]
Revenues	1,008,688	889,624	2,896,778	2,672,695
Domestic | Fixed-price
Disaggregation Of Revenue [Line Items]
Revenues	494,095	468,116	1,420,858	1,242,601
Domestic | Time-and-materials
Disaggregation Of Revenue [Line Items]
Revenues	191,696	175,140	540,913	499,556
International
Disaggregation Of Revenue [Line Items]
Revenues	49,791	51,100	140,896	145,804
International | Expertise
Disaggregation Of Revenue [Line Items]
Revenues	18,307	18,852	50,977	56,374
International | Technology
Disaggregation Of Revenue [Line Items]
Revenues	31,484	32,248	89,919	89,430
International | Prime contractor
Disaggregation Of Revenue [Line Items]
Revenues	44,975	46,760	128,303	132,983
International | Subcontractor
Disaggregation Of Revenue [Line Items]
Revenues	4,816	4,340	12,593	12,821
International | Department of Defense
Disaggregation Of Revenue [Line Items]
Revenues	0	0	0	0
International | Federal Civilian agencies
Disaggregation Of Revenue [Line Items]
Revenues	0	0	0	0
International | Commercial and other
Disaggregation Of Revenue [Line Items]
Revenues	49,791	51,100	140,896	145,804
International | Cost-plus-fee
Disaggregation Of Revenue [Line Items]
Revenues	0	0	0	0
International | Fixed-price
Disaggregation Of Revenue [Line Items]
Revenues	35,691	35,058	100,057	101,568
International | Time-and-materials
Disaggregation Of Revenue [Line Items]
Revenues	$ 14,100	$ 16,042	$ 40,839	$ 44,236