Revenues and Contract Balances - Disaggregation of Revenues (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Mar. 31, 2025	Mar. 31, 2024	Mar. 31, 2025	Mar. 31, 2024
Disaggregation Of Revenue [Line Items]
Revenues	$ 2,166,982	$ 1,937,456	$ 6,323,680	$ 5,621,537
Expertise
Disaggregation Of Revenue [Line Items]
Revenues	973,037	916,955	2,887,202	2,644,590
Technology
Disaggregation Of Revenue [Line Items]
Revenues	1,193,945	1,020,501	3,436,478	2,976,947
Prime contractor
Disaggregation Of Revenue [Line Items]
Revenues	1,955,753	1,741,777	5,698,270	5,027,516
Subcontractor
Disaggregation Of Revenue [Line Items]
Revenues	211,229	195,679	625,410	594,021
Department of Defense
Disaggregation Of Revenue [Line Items]
Revenues	1,652,206	1,452,264	4,765,472	4,163,079
Federal civilian agencies
Disaggregation Of Revenue [Line Items]
Revenues	431,453	381,214	1,304,515	1,178,500
Commercial and other
Disaggregation Of Revenue [Line Items]
Revenues	83,323	103,978	253,693	279,958
Cost-plus-fee
Disaggregation Of Revenue [Line Items]
Revenues	1,316,805	1,174,219	3,837,028	3,411,128
Fixed-price
Disaggregation Of Revenue [Line Items]
Revenues	573,464	520,987	1,651,579	1,542,608
Time-and-materials
Disaggregation Of Revenue [Line Items]
Revenues	276,713	242,250	835,073	667,801
Domestic
Disaggregation Of Revenue [Line Items]
Revenues	2,105,120	1,877,986	6,140,597	5,453,162
Domestic \| Expertise
Disaggregation Of Revenue [Line Items]
Revenues	941,805	895,791	2,794,191	2,583,634
Domestic \| Technology
Disaggregation Of Revenue [Line Items]
Revenues	1,163,315	982,195	3,346,406	2,869,528
Domestic \| Prime contractor
Disaggregation Of Revenue [Line Items]
Revenues	1,900,648	1,689,140	5,535,517	4,878,820
Domestic \| Subcontractor
Disaggregation Of Revenue [Line Items]
Revenues	204,472	188,846	605,080	574,342
Domestic \| Department of Defense
Disaggregation Of Revenue [Line Items]
Revenues	1,652,206	1,452,264	4,765,472	4,163,079
Domestic \| Federal civilian agencies
Disaggregation Of Revenue [Line Items]
Revenues	431,453	381,214	1,304,515	1,178,500
Domestic \| Commercial and other
Disaggregation Of Revenue [Line Items]
Revenues	21,461	44,508	70,610	111,583
Domestic \| Cost-plus-fee
Disaggregation Of Revenue [Line Items]
Revenues	1,316,805	1,174,219	3,837,028	3,411,128
Domestic \| Fixed-price
Disaggregation Of Revenue [Line Items]
Revenues	533,735	484,980	1,537,759	1,437,282
Domestic \| Time-and-materials
Disaggregation Of Revenue [Line Items]
Revenues	254,580	218,787	765,810	604,752
International
Disaggregation Of Revenue [Line Items]
Revenues	61,862	59,470	183,083	168,375
International \| Expertise
Disaggregation Of Revenue [Line Items]
Revenues	31,232	21,164	93,011	60,956
International \| Technology
Disaggregation Of Revenue [Line Items]
Revenues	30,630	38,306	90,072	107,419
International \| Prime contractor
Disaggregation Of Revenue [Line Items]
Revenues	55,105	52,637	162,753	148,696
International \| Subcontractor
Disaggregation Of Revenue [Line Items]
Revenues	6,757	6,833	20,330	19,679
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	61,862	59,470	183,083	168,375
International \| Cost-plus-fee
Disaggregation Of Revenue [Line Items]
Revenues	0	0	0	0
International \| Fixed-price
Disaggregation Of Revenue [Line Items]
Revenues	39,729	36,007	113,820	105,326
International \| Time-and-materials
Disaggregation Of Revenue [Line Items]
Revenues	$ 22,133	$ 23,463	$ 69,263	$ 63,049