Revenues and Contract Balances - Disaggregation of Revenues (Details) - USD ($) $ in Thousands	3 Months Ended
	Sep. 30, 2024	Sep. 30, 2023
Disaggregation Of Revenue [Line Items]
Revenues	$ 2,056,889	$ 1,850,147
Expertise
Disaggregation Of Revenue [Line Items]
Revenues	988,265	878,094
Technology
Disaggregation Of Revenue [Line Items]
Revenues	1,068,624	972,053
Prime contractor
Disaggregation Of Revenue [Line Items]
Revenues	1,880,419	1,649,362
Subcontractor
Disaggregation Of Revenue [Line Items]
Revenues	176,470	200,785
Department of Defense
Disaggregation Of Revenue [Line Items]
Revenues	1,534,533	1,352,306
Federal civilian agencies
Disaggregation Of Revenue [Line Items]
Revenues	439,371	407,344
Commercial and other
Disaggregation Of Revenue [Line Items]
Revenues	82,985	90,497
Cost-plus-fee
Disaggregation Of Revenue [Line Items]
Revenues	1,280,010	1,134,435
Fixed-price
Disaggregation Of Revenue [Line Items]
Revenues	475,256	502,077
Time-and-materials
Disaggregation Of Revenue [Line Items]
Revenues	301,623	213,635
Domestic
Disaggregation Of Revenue [Line Items]
Revenues	1,996,321	1,795,168
Domestic | Expertise
Disaggregation Of Revenue [Line Items]
Revenues	956,496	857,196
Domestic | Technology
Disaggregation Of Revenue [Line Items]
Revenues	1,039,825	937,972
Domestic | Prime contractor
Disaggregation Of Revenue [Line Items]
Revenues	1,826,763	1,601,091
Domestic | Subcontractor
Disaggregation Of Revenue [Line Items]
Revenues	169,558	194,077
Domestic | Department of Defense
Disaggregation Of Revenue [Line Items]
Revenues	1,534,533	1,352,306
Domestic | Federal civilian agencies
Disaggregation Of Revenue [Line Items]
Revenues	439,371	407,344
Domestic | Commercial and other
Disaggregation Of Revenue [Line Items]
Revenues	22,417	35,518
Domestic | Cost-plus-fee
Disaggregation Of Revenue [Line Items]
Revenues	1,280,010	1,134,435
Domestic | Fixed-price
Disaggregation Of Revenue [Line Items]
Revenues	439,240	467,216
Domestic | Time-and-materials
Disaggregation Of Revenue [Line Items]
Revenues	277,071	193,517
International
Disaggregation Of Revenue [Line Items]
Revenues	60,568	54,979
International | Expertise
Disaggregation Of Revenue [Line Items]
Revenues	31,769	20,898
International | Technology
Disaggregation Of Revenue [Line Items]
Revenues	28,799	34,081
International | Prime contractor
Disaggregation Of Revenue [Line Items]
Revenues	53,656	48,271
International | Subcontractor
Disaggregation Of Revenue [Line Items]
Revenues	6,912	6,708
International | Department of Defense
Disaggregation Of Revenue [Line Items]
Revenues	0	0
International | Federal civilian agencies
Disaggregation Of Revenue [Line Items]
Revenues	0	0
International | Commercial and other
Disaggregation Of Revenue [Line Items]
Revenues	60,568	54,979
International | Cost-plus-fee
Disaggregation Of Revenue [Line Items]
Revenues	0	0
International | Fixed-price
Disaggregation Of Revenue [Line Items]
Revenues	36,016	34,861
International | Time-and-materials
Disaggregation Of Revenue [Line Items]
Revenues	$ 24,552	$ 20,118