Revenues and Contract Balances - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2022	Dec. 31, 2021
Disaggregation Of Revenue [Line Items]
Revenues	$ 1,649,416	$ 1,485,778	$ 3,255,175	$ 2,976,676
Expertise
Disaggregation Of Revenue [Line Items]
Revenues	741,620	686,309	1,475,823	1,389,355
Technology
Disaggregation Of Revenue [Line Items]
Revenues	907,796	799,469	1,779,352	1,587,321
Prime contractor
Disaggregation Of Revenue [Line Items]
Revenues	1,460,839	1,335,846	2,911,149	2,677,405
Subcontractor
Disaggregation Of Revenue [Line Items]
Revenues	188,577	149,932	344,026	299,271
Department of Defense
Disaggregation Of Revenue [Line Items]
Revenues	1,160,060	1,037,014	2,255,380	2,037,141
Federal civilian agencies
Disaggregation Of Revenue [Line Items]
Revenues	399,768	371,897	823,855	785,561
Commercial and other
Disaggregation Of Revenue [Line Items]
Revenues	89,588	76,867	175,940	153,974
Cost-plus-fee
Disaggregation Of Revenue [Line Items]
Revenues	953,344	889,358	1,888,090	1,783,071
Fixed-price
Disaggregation Of Revenue [Line Items]
Revenues	509,356	433,290	991,129	840,995
Time and materials
Disaggregation Of Revenue [Line Items]
Revenues	186,716	163,130	375,956	352,610
Domestic
Disaggregation Of Revenue [Line Items]
Revenues	1,605,175	1,438,250	3,164,070	2,881,972
Domestic | Expertise
Disaggregation Of Revenue [Line Items]
Revenues	725,503	668,209	1,443,153	1,351,833
Domestic | Technology
Disaggregation Of Revenue [Line Items]
Revenues	879,672	770,041	1,720,917	1,530,139
Domestic | Prime contractor
Disaggregation Of Revenue [Line Items]
Revenues	1,420,367	1,292,529	2,827,821	2,591,182
Domestic | Subcontractor
Disaggregation Of Revenue [Line Items]
Revenues	184,808	145,721	336,249	290,790
Domestic | Department of Defense
Disaggregation Of Revenue [Line Items]
Revenues	1,160,060	1,037,014	2,255,380	2,037,141
Domestic | Federal civilian agencies
Disaggregation Of Revenue [Line Items]
Revenues	399,768	371,897	823,855	785,561
Domestic | Commercial and other
Disaggregation Of Revenue [Line Items]
Revenues	45,347	29,339	84,835	59,270
Domestic | Cost-plus-fee
Disaggregation Of Revenue [Line Items]
Revenues	953,344	889,358	1,888,090	1,783,071
Domestic | Fixed-price
Disaggregation Of Revenue [Line Items]
Revenues	478,201	400,011	926,763	774,485
Domestic | Time and materials
Disaggregation Of Revenue [Line Items]
Revenues	173,630	148,881	349,217	324,416
International
Disaggregation Of Revenue [Line Items]
Revenues	44,241	47,528	91,105	94,704
International | Expertise
Disaggregation Of Revenue [Line Items]
Revenues	16,117	18,100	32,670	37,522
International | Technology
Disaggregation Of Revenue [Line Items]
Revenues	28,124	29,428	58,435	57,182
International | Prime contractor
Disaggregation Of Revenue [Line Items]
Revenues	40,472	43,317	83,328	86,223
International | Subcontractor
Disaggregation Of Revenue [Line Items]
Revenues	3,769	4,211	7,777	8,481
International | Commercial and other
Disaggregation Of Revenue [Line Items]
Revenues	44,241	47,528	91,105	94,704
International | Fixed-price
Disaggregation Of Revenue [Line Items]
Revenues	31,155	33,279	64,366	66,510
International | Time and materials
Disaggregation Of Revenue [Line Items]
Revenues	$ 13,086	$ 14,249	$ 26,739	$ 28,194