Revenues and Contract Balances - Disaggregation of Revenues (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Mar. 31, 2024	Mar. 31, 2023
Disaggregation Of Revenue [Line Items]
Revenues	$ 1,937,456	$ 1,744,270	$ 5,621,537	$ 4,999,445
Expertise
Disaggregation Of Revenue [Line Items]
Revenues	916,955	812,300	2,644,590	2,288,123
Technology
Disaggregation Of Revenue [Line Items]
Revenues	1,020,501	931,970	2,976,947	2,711,322
Prime contractor
Disaggregation Of Revenue [Line Items]
Revenues	1,741,777	1,556,733	5,027,516	4,467,882
Subcontractor
Disaggregation Of Revenue [Line Items]
Revenues	195,679	187,537	594,021	531,563
Department of Defense
Disaggregation Of Revenue [Line Items]
Revenues	1,452,264	1,298,700	4,163,079	3,554,080
Federal civilian agencies
Disaggregation Of Revenue [Line Items]
Revenues	381,214	355,612	1,178,500	1,179,467
Commercial and other
Disaggregation Of Revenue [Line Items]
Revenues	103,978	89,958	279,958	265,898
Cost-plus-fee
Disaggregation Of Revenue [Line Items]
Revenues	1,174,219	1,008,688	3,411,128	2,896,778
Fixed-price
Disaggregation Of Revenue [Line Items]
Revenues	520,987	529,786	1,542,608	1,520,915
Time-and-materials
Disaggregation Of Revenue [Line Items]
Revenues	242,250	205,796	667,801	581,752
Domestic
Disaggregation Of Revenue [Line Items]
Revenues	1,877,986	1,694,479	5,453,162	4,858,549
Domestic | Expertise
Disaggregation Of Revenue [Line Items]
Revenues	895,791	793,993	2,583,634	2,237,146
Domestic | Technology
Disaggregation Of Revenue [Line Items]
Revenues	982,195	900,486	2,869,528	2,621,403
Domestic | Prime contractor
Disaggregation Of Revenue [Line Items]
Revenues	1,689,140	1,511,758	4,878,820	4,339,579
Domestic | Subcontractor
Disaggregation Of Revenue [Line Items]
Revenues	188,846	182,721	574,342	518,970
Domestic | Department of Defense
Disaggregation Of Revenue [Line Items]
Revenues	1,452,264	1,298,700	4,163,079	3,554,080
Domestic | Federal civilian agencies
Disaggregation Of Revenue [Line Items]
Revenues	381,214	355,612	1,178,500	1,179,467
Domestic | Commercial and other
Disaggregation Of Revenue [Line Items]
Revenues	44,508	40,167	111,583	125,002
Domestic | Cost-plus-fee
Disaggregation Of Revenue [Line Items]
Revenues	1,174,219	1,008,688	3,411,128	2,896,778
Domestic | Fixed-price
Disaggregation Of Revenue [Line Items]
Revenues	484,980	494,095	1,437,282	1,420,858
Domestic | Time-and-materials
Disaggregation Of Revenue [Line Items]
Revenues	218,787	191,696	604,752	540,913
International
Disaggregation Of Revenue [Line Items]
Revenues	59,470	49,791	168,375	140,896
International | Expertise
Disaggregation Of Revenue [Line Items]
Revenues	21,164	18,307	60,956	50,977
International | Technology
Disaggregation Of Revenue [Line Items]
Revenues	38,306	31,484	107,419	89,919
International | Prime contractor
Disaggregation Of Revenue [Line Items]
Revenues	52,637	44,975	148,696	128,303
International | Subcontractor
Disaggregation Of Revenue [Line Items]
Revenues	6,833	4,816	19,679	12,593
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	59,470	49,791	168,375	140,896
International | Cost-plus-fee
Disaggregation Of Revenue [Line Items]
Revenues	0	0	0	0
International | Fixed-price
Disaggregation Of Revenue [Line Items]
Revenues	36,007	35,691	105,326	100,057
International | Time-and-materials
Disaggregation Of Revenue [Line Items]
Revenues	$ 23,463	$ 14,100	$ 63,049	$ 40,839