Revenues and Contract Balances - Disaggregation of Revenues (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2024	Dec. 31, 2023
Disaggregation Of Revenue [Line Items]
Revenues	$ 2,099,809	$ 1,833,934	$ 4,156,698	$ 3,684,081
Expertise
Disaggregation Of Revenue [Line Items]
Revenues	925,900	849,541	1,914,165	1,727,635
Technology
Disaggregation Of Revenue [Line Items]
Revenues	1,173,909	984,393	2,242,533	1,956,446
Prime contractor
Disaggregation Of Revenue [Line Items]
Revenues	1,862,098	1,636,377	3,742,517	3,285,739
Subcontractor
Disaggregation Of Revenue [Line Items]
Revenues	237,711	197,557	414,181	398,342
Department of Defense
Disaggregation Of Revenue [Line Items]
Revenues	1,578,733	1,358,509	3,113,266	2,710,815
Federal civilian agencies
Disaggregation Of Revenue [Line Items]
Revenues	433,691	389,942	873,062	797,286
Commercial and other
Disaggregation Of Revenue [Line Items]
Revenues	87,385	85,483	170,370	175,980
Cost-plus-fee
Disaggregation Of Revenue [Line Items]
Revenues	1,240,213	1,102,474	2,520,223	2,236,909
Fixed-price
Disaggregation Of Revenue [Line Items]
Revenues	602,859	519,544	1,078,115	1,021,621
Time-and-materials
Disaggregation Of Revenue [Line Items]
Revenues	256,737	211,916	558,360	425,551
Domestic
Disaggregation Of Revenue [Line Items]
Revenues	2,039,156	1,780,008	4,035,477	3,575,176
Domestic | Expertise
Disaggregation Of Revenue [Line Items]
Revenues	895,890	830,647	1,852,386	1,687,843
Domestic | Technology
Disaggregation Of Revenue [Line Items]
Revenues	1,143,266	949,361	2,183,091	1,887,333
Domestic | Prime contractor
Disaggregation Of Revenue [Line Items]
Revenues	1,808,106	1,588,589	3,634,869	3,189,680
Domestic | Subcontractor
Disaggregation Of Revenue [Line Items]
Revenues	231,050	191,419	400,608	385,496
Domestic | Department of Defense
Disaggregation Of Revenue [Line Items]
Revenues	1,578,733	1,358,509	3,113,266	2,710,815
Domestic | Federal civilian agencies
Disaggregation Of Revenue [Line Items]
Revenues	433,691	389,942	873,062	797,286
Domestic | Commercial and other
Disaggregation Of Revenue [Line Items]
Revenues	26,732	31,557	49,149	67,075
Domestic | Cost-plus-fee
Disaggregation Of Revenue [Line Items]
Revenues	1,240,213	1,102,474	2,520,223	2,236,909
Domestic | Fixed-price
Disaggregation Of Revenue [Line Items]
Revenues	564,784	485,086	1,004,024	952,302
Domestic | Time-and-materials
Disaggregation Of Revenue [Line Items]
Revenues	234,159	192,448	511,230	385,965
International
Disaggregation Of Revenue [Line Items]
Revenues	60,653	53,926	121,221	108,905
International | Expertise
Disaggregation Of Revenue [Line Items]
Revenues	30,010	18,894	61,779	39,792
International | Technology
Disaggregation Of Revenue [Line Items]
Revenues	30,643	35,032	59,442	69,113
International | Prime contractor
Disaggregation Of Revenue [Line Items]
Revenues	53,992	47,788	107,648	96,059
International | Subcontractor
Disaggregation Of Revenue [Line Items]
Revenues	6,661	6,138	13,573	12,846
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	60,653	53,926	121,221	108,905
International | Cost-plus-fee
Disaggregation Of Revenue [Line Items]
Revenues	0	0	0	0
International | Fixed-price
Disaggregation Of Revenue [Line Items]
Revenues	38,075	34,458	74,091	69,319
International | Time-and-materials
Disaggregation Of Revenue [Line Items]
Revenues	$ 22,578	$ 19,468	$ 47,130	$ 39,586