Revenues and Contract Balances - Disaggregation of Revenues (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2023	Dec. 31, 2022
Disaggregation Of Revenue [Line Items]
Revenues	$ 1,833,934	$ 1,649,416	$ 3,684,081	$ 3,255,175
Expertise
Disaggregation Of Revenue [Line Items]
Revenues	849,541	741,620	1,727,635	1,475,823
Technology
Disaggregation Of Revenue [Line Items]
Revenues	984,393	907,796	1,956,446	1,779,352
Prime contractor
Disaggregation Of Revenue [Line Items]
Revenues	1,636,377	1,460,839	3,285,739	2,911,149
Subcontractor
Disaggregation Of Revenue [Line Items]
Revenues	197,557	188,577	398,342	344,026
Department of Defense
Disaggregation Of Revenue [Line Items]
Revenues	1,358,509	1,160,060	2,710,815	2,255,380
Federal civilian agencies
Disaggregation Of Revenue [Line Items]
Revenues	389,942	399,768	797,286	823,855
Commercial and other
Disaggregation Of Revenue [Line Items]
Revenues	85,483	89,588	175,980	175,940
Cost-plus-fee
Disaggregation Of Revenue [Line Items]
Revenues	1,102,474	953,344	2,236,909	1,888,090
Fixed-price
Disaggregation Of Revenue [Line Items]
Revenues	519,544	509,356	1,021,621	991,129
Time-and-materials
Disaggregation Of Revenue [Line Items]
Revenues	211,916	186,716	425,551	375,956
Domestic
Disaggregation Of Revenue [Line Items]
Revenues	1,780,008	1,605,175	3,575,176	3,164,070
Domestic | Expertise
Disaggregation Of Revenue [Line Items]
Revenues	830,647	725,503	1,687,843	1,443,153
Domestic | Technology
Disaggregation Of Revenue [Line Items]
Revenues	949,361	879,672	1,887,333	1,720,917
Domestic | Prime contractor
Disaggregation Of Revenue [Line Items]
Revenues	1,588,589	1,420,367	3,189,680	2,827,821
Domestic | Subcontractor
Disaggregation Of Revenue [Line Items]
Revenues	191,419	184,808	385,496	336,249
Domestic | Department of Defense
Disaggregation Of Revenue [Line Items]
Revenues	1,358,509	1,160,060	2,710,815	2,255,380
Domestic | Federal civilian agencies
Disaggregation Of Revenue [Line Items]
Revenues	389,942	399,768	797,286	823,855
Domestic | Commercial and other
Disaggregation Of Revenue [Line Items]
Revenues	31,557	45,347	67,075	84,835
Domestic | Cost-plus-fee
Disaggregation Of Revenue [Line Items]
Revenues	1,102,474	953,344	2,236,909	1,888,090
Domestic | Fixed-price
Disaggregation Of Revenue [Line Items]
Revenues	485,086	478,201	952,302	926,763
Domestic | Time-and-materials
Disaggregation Of Revenue [Line Items]
Revenues	192,448	173,630	385,965	349,217
International
Disaggregation Of Revenue [Line Items]
Revenues	53,926	44,241	108,905	91,105
International | Expertise
Disaggregation Of Revenue [Line Items]
Revenues	18,894	16,117	39,792	32,670
International | Technology
Disaggregation Of Revenue [Line Items]
Revenues	35,032	28,124	69,113	58,435
International | Prime contractor
Disaggregation Of Revenue [Line Items]
Revenues	47,788	40,472	96,059	83,328
International | Subcontractor
Disaggregation Of Revenue [Line Items]
Revenues	6,138	3,769	12,846	7,777
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	53,926	44,241	108,905	91,105
International | Cost-plus-fee
Disaggregation Of Revenue [Line Items]
Revenues	0	0	0	0
International | Fixed-price
Disaggregation Of Revenue [Line Items]
Revenues	34,458	31,155	69,319	64,366
International | Time-and-materials
Disaggregation Of Revenue [Line Items]
Revenues	$ 19,468	$ 13,086	$ 39,586	$ 26,739