Revenue Recognition - Disaggregation of Revenue (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020
Disaggregation Of Revenue [Line Items]
Revenue	$ 1,551,918	$ 1,465,600	$ 4,480,135	$ 4,224,461
Expertise
Disaggregation Of Revenue [Line Items]
Revenue	764,419	763,336	2,237,378	2,227,723
Technology
Disaggregation Of Revenue [Line Items]
Revenue	787,499	702,264	2,242,757	1,996,738
Prime contractor
Disaggregation Of Revenue [Line Items]
Revenue	1,401,633	1,340,861	4,055,496	3,842,621
Subcontractor
Disaggregation Of Revenue [Line Items]
Revenue	150,285	124,739	424,639	381,840
Department of Defense
Disaggregation Of Revenue [Line Items]
Revenue	1,074,056	1,037,242	3,091,126	2,965,263
Federal civilian agencies
Disaggregation Of Revenue [Line Items]
Revenue	405,855	361,320	1,186,068	1,067,342
Commercial and other
Disaggregation Of Revenue [Line Items]
Revenue	72,007	67,038	202,941	191,856
Cost-plus-fee
Disaggregation Of Revenue [Line Items]
Revenue	905,774	852,700	2,572,967	2,418,891
Fixed-price
Disaggregation Of Revenue [Line Items]
Revenue	457,099	405,736	1,331,734	1,212,579
Time and materials
Disaggregation Of Revenue [Line Items]
Revenue	189,045	207,164	575,434	592,991
Domestic
Disaggregation Of Revenue [Line Items]
Revenue	1,505,037	1,419,358	4,350,284	4,097,924
Domestic | Expertise
Disaggregation Of Revenue [Line Items]
Revenue	745,440	744,997	2,184,449	2,180,498
Domestic | Technology
Disaggregation Of Revenue [Line Items]
Revenue	759,597	674,361	2,165,835	1,917,426
Domestic | Prime contractor
Disaggregation Of Revenue [Line Items]
Revenue	1,358,423	1,298,073	3,935,661	3,723,024
Domestic | Subcontractor
Disaggregation Of Revenue [Line Items]
Revenue	146,614	121,285	414,623	374,900
Domestic | Department of Defense
Disaggregation Of Revenue [Line Items]
Revenue	1,074,056	1,037,242	3,091,126	2,965,263
Domestic | Federal civilian agencies
Disaggregation Of Revenue [Line Items]
Revenue	405,855	361,320	1,186,068	1,067,342
Domestic | Commercial and other
Disaggregation Of Revenue [Line Items]
Revenue	25,126	20,796	73,090	65,319
Domestic | Cost-plus-fee
Disaggregation Of Revenue [Line Items]
Revenue	905,774	852,700	2,572,967	2,418,891
Domestic | Fixed-price
Disaggregation Of Revenue [Line Items]
Revenue	424,580	376,314	1,245,278	1,128,866
Domestic | Time and materials
Disaggregation Of Revenue [Line Items]
Revenue	174,683	190,344	532,039	550,167
International
Disaggregation Of Revenue [Line Items]
Revenue	46,881	46,242	129,851	126,537
International | Expertise
Disaggregation Of Revenue [Line Items]
Revenue	18,979	18,339	52,929	47,225
International | Technology
Disaggregation Of Revenue [Line Items]
Revenue	27,902	27,903	76,922	79,312
International | Prime contractor
Disaggregation Of Revenue [Line Items]
Revenue	43,210	42,788	119,835	119,597
International | Subcontractor
Disaggregation Of Revenue [Line Items]
Revenue	3,671	3,454	10,016	6,940
International | Commercial and other
Disaggregation Of Revenue [Line Items]
Revenue	46,881	46,242	129,851	126,537
International | Fixed-price
Disaggregation Of Revenue [Line Items]
Revenue	32,519	29,422	86,456	83,713
International | Time and materials
Disaggregation Of Revenue [Line Items]
Revenue	$ 14,362	$ 16,820	$ 43,395	$ 42,824