Revenues and Contract Balances - Disaggregation of Revenues (Details) - USD ($) $ in Thousands	3 Months Ended
	Sep. 30, 2023	Sep. 30, 2022
Disaggregation Of Revenue [Line Items]
Revenues	$ 1,850,147	$ 1,605,759
Expertise
Disaggregation Of Revenue [Line Items]
Revenues	878,094	734,203
Technology
Disaggregation Of Revenue [Line Items]
Revenues	972,053	871,556
Prime contractor
Disaggregation Of Revenue [Line Items]
Revenues	1,649,362	1,450,310
Subcontractor
Disaggregation Of Revenue [Line Items]
Revenues	200,785	155,449
Department of Defense
Disaggregation Of Revenue [Line Items]
Revenues	1,352,306	1,095,320
Federal civilian agencies
Disaggregation Of Revenue [Line Items]
Revenues	407,344	424,087
Commercial and other
Disaggregation Of Revenue [Line Items]
Revenues	90,497	86,352
Cost-plus-fee
Disaggregation Of Revenue [Line Items]
Revenues	1,134,435	934,746
Fixed-price
Disaggregation Of Revenue [Line Items]
Revenues	502,077	481,773
Time-and-materials
Disaggregation Of Revenue [Line Items]
Revenues	213,635	189,240
Domestic
Disaggregation Of Revenue [Line Items]
Revenues	1,795,168	1,558,895
Domestic | Expertise
Disaggregation Of Revenue [Line Items]
Revenues	857,196	717,650
Domestic | Technology
Disaggregation Of Revenue [Line Items]
Revenues	937,972	841,245
Domestic | Prime contractor
Disaggregation Of Revenue [Line Items]
Revenues	1,601,091	1,407,454
Domestic | Subcontractor
Disaggregation Of Revenue [Line Items]
Revenues	194,077	151,441
Domestic | Department of Defense
Disaggregation Of Revenue [Line Items]
Revenues	1,352,306	1,095,320
Domestic | Federal civilian agencies
Disaggregation Of Revenue [Line Items]
Revenues	407,344	424,087
Domestic | Commercial and other
Disaggregation Of Revenue [Line Items]
Revenues	35,518	39,488
Domestic | Cost-plus-fee
Disaggregation Of Revenue [Line Items]
Revenues	1,134,435	934,746
Domestic | Fixed-price
Disaggregation Of Revenue [Line Items]
Revenues	467,216	448,562
Domestic | Time-and-materials
Disaggregation Of Revenue [Line Items]
Revenues	193,517	175,587
International
Disaggregation Of Revenue [Line Items]
Revenues	54,979	46,864
International | Expertise
Disaggregation Of Revenue [Line Items]
Revenues	20,898	16,553
International | Technology
Disaggregation Of Revenue [Line Items]
Revenues	34,081	30,311
International | Prime contractor
Disaggregation Of Revenue [Line Items]
Revenues	48,271	42,856
International | Subcontractor
Disaggregation Of Revenue [Line Items]
Revenues	6,708	4,008
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	54,979	46,864
International | Cost-plus-fee
Disaggregation Of Revenue [Line Items]
Revenues	0	0
International | Fixed-price
Disaggregation Of Revenue [Line Items]
Revenues	34,861	33,211
International | Time-and-materials
Disaggregation Of Revenue [Line Items]
Revenues	$ 20,118	$ 13,653