Revenue Recognition - Disaggregation of Revenue by Contract Type, Customer Information and Prime or Subcontractor (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2019	Dec. 31, 2018
Disaggregation Of Revenue [Line Items]
Revenue	$ 1,395,469	$ 1,181,641	$ 2,758,861	$ 2,347,505
Prime contractor
Disaggregation Of Revenue [Line Items]
Revenue	1,268,993	1,091,956	2,505,246	2,181,828
Subcontractor
Disaggregation Of Revenue [Line Items]
Revenue	126,476	89,685	253,615	165,677
Department of Defense
Disaggregation Of Revenue [Line Items]
Revenue	990,381	834,797	1,928,021	1,653,063
Federal civilian agencies
Disaggregation Of Revenue [Line Items]
Revenue	342,029	287,915	706,022	580,117
Commercial and other
Disaggregation Of Revenue [Line Items]
Revenue	63,059	58,929	124,818	114,325
Cost-plus-fee
Disaggregation Of Revenue [Line Items]
Revenue	818,477	657,050	1,566,191	1,298,577
Firm fixed-price
Disaggregation Of Revenue [Line Items]
Revenue	388,867	337,374	806,843	681,378
Time and materials
Disaggregation Of Revenue [Line Items]
Revenue	188,125	187,217	385,827	367,550
Domestic
Disaggregation Of Revenue [Line Items]
Revenue	1,353,793	1,142,552	2,678,566	2,269,075
Domestic | Prime contractor
Disaggregation Of Revenue [Line Items]
Revenue	1,227,317	1,052,867	2,424,951	2,103,398
Domestic | Subcontractor
Disaggregation Of Revenue [Line Items]
Revenue	126,476	89,685	253,615	165,677
Domestic | Department of Defense
Disaggregation Of Revenue [Line Items]
Revenue	990,381	834,797	1,928,021	1,653,063
Domestic | Federal civilian agencies
Disaggregation Of Revenue [Line Items]
Revenue	342,029	287,915	706,022	580,117
Domestic | Commercial and other
Disaggregation Of Revenue [Line Items]
Revenue	21,383	19,840	44,523	35,895
Domestic | Cost-plus-fee
Disaggregation Of Revenue [Line Items]
Revenue	818,477	657,050	1,566,191	1,298,577
Domestic | Firm fixed-price
Disaggregation Of Revenue [Line Items]
Revenue	361,016	313,018	752,552	634,089
Domestic | Time and materials
Disaggregation Of Revenue [Line Items]
Revenue	174,300	172,484	359,823	336,409
International
Disaggregation Of Revenue [Line Items]
Revenue	41,676	39,089	80,295	78,430
International | Prime contractor
Disaggregation Of Revenue [Line Items]
Revenue	41,676	39,089	80,295	78,430
International | Commercial and other
Disaggregation Of Revenue [Line Items]
Revenue	41,676	39,089	80,295	78,430
International | Firm fixed-price
Disaggregation Of Revenue [Line Items]
Revenue	27,851	24,356	54,291	47,289
International | Time and materials
Disaggregation Of Revenue [Line Items]
Revenue	$ 13,825	$ 14,733	$ 26,004	$ 31,141