Revenues and Contract Balances - Disaggregation of Revenues (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Mar. 31, 2026	Mar. 31, 2025	Mar. 31, 2026	Mar. 31, 2025
Disaggregation Of Revenue [Line Items]
Revenues	$ 2,351,002	$ 2,166,982	$ 6,858,722	$ 6,323,680
Expertise
Disaggregation Of Revenue [Line Items]
Revenues	1,023,728	973,037	2,934,820	2,887,202
Technology
Disaggregation Of Revenue [Line Items]
Revenues	1,327,274	1,193,945	3,923,902	3,436,478
Prime contractor
Disaggregation Of Revenue [Line Items]
Revenues	2,125,078	1,955,753	6,211,546	5,698,270
Subcontractor
Disaggregation Of Revenue [Line Items]
Revenues	225,924	211,229	647,176	625,410
Department of Defense
Disaggregation Of Revenue [Line Items]
Revenues	1,295,628	1,180,820	3,627,406	3,387,095
Intelligence Community
Disaggregation Of Revenue [Line Items]
Revenues	582,235	552,796	1,717,704	1,614,883
Federal civilian agencies
Disaggregation Of Revenue [Line Items]
Revenues	373,582	350,044	1,223,944	1,068,005
Commercial and other
Disaggregation Of Revenue [Line Items]
Revenues	99,557	83,322	289,668	253,697
Cost-plus-fee
Disaggregation Of Revenue [Line Items]
Revenues	1,273,227	1,316,805	3,965,968	3,837,028
Fixed-price
Disaggregation Of Revenue [Line Items]
Revenues	749,908	573,464	1,959,418	1,651,579
Time-and-materials
Disaggregation Of Revenue [Line Items]
Revenues	327,867	276,713	933,336	835,073
Domestic
Disaggregation Of Revenue [Line Items]
Revenues	2,273,695	2,105,120	6,628,722	6,140,597
Domestic | Expertise
Disaggregation Of Revenue [Line Items]
Revenues	971,645	941,805	2,784,290	2,794,191
Domestic | Technology
Disaggregation Of Revenue [Line Items]
Revenues	1,302,050	1,163,315	3,844,432	3,346,406
Domestic | Prime contractor
Disaggregation Of Revenue [Line Items]
Revenues	2,057,271	1,900,648	6,006,308	5,535,517
Domestic | Subcontractor
Disaggregation Of Revenue [Line Items]
Revenues	216,424	204,472	622,414	605,080
Domestic | Department of Defense
Disaggregation Of Revenue [Line Items]
Revenues	1,295,628	1,180,820	3,627,406	3,387,095
Domestic | Intelligence Community
Disaggregation Of Revenue [Line Items]
Revenues	582,235	552,796	1,717,704	1,614,883
Domestic | Federal civilian agencies
Disaggregation Of Revenue [Line Items]
Revenues	373,582	350,044	1,223,944	1,068,005
Domestic | Commercial and other
Disaggregation Of Revenue [Line Items]
Revenues	22,250	21,460	59,668	70,614
Domestic | Cost-plus-fee
Disaggregation Of Revenue [Line Items]
Revenues	1,273,227	1,316,805	3,965,968	3,837,028
Domestic | Fixed-price
Disaggregation Of Revenue [Line Items]
Revenues	703,042	533,735	1,822,855	1,537,759
Domestic | Time-and-materials
Disaggregation Of Revenue [Line Items]
Revenues	297,426	254,580	839,899	765,810
International
Disaggregation Of Revenue [Line Items]
Revenues	77,307	61,862	230,000	183,083
International | Expertise
Disaggregation Of Revenue [Line Items]
Revenues	52,083	31,232	150,530	93,011
International | Technology
Disaggregation Of Revenue [Line Items]
Revenues	25,224	30,630	79,470	90,072
International | Prime contractor
Disaggregation Of Revenue [Line Items]
Revenues	67,807	55,105	205,238	162,753
International | Subcontractor
Disaggregation Of Revenue [Line Items]
Revenues	9,500	6,757	24,762	20,330
International | Department of Defense
Disaggregation Of Revenue [Line Items]
Revenues	0	0	0	0
International | Intelligence Community
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	77,307	61,862	230,000	183,083
International | Cost-plus-fee
Disaggregation Of Revenue [Line Items]
Revenues	0	0	0	0
International | Fixed-price
Disaggregation Of Revenue [Line Items]
Revenues	46,866	39,729	136,563	113,820
International | Time-and-materials
Disaggregation Of Revenue [Line Items]
Revenues	$ 30,441	$ 22,133	$ 93,437	$ 69,263