Revenue Recognition - Disaggregation of Revenue by Contract Type, Customer Information and Prime or Subcontractor (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2020	Mar. 31, 2019
Disaggregation Of Revenue [Line Items]
Revenue	$ 1,465,600	$ 1,264,958	$ 4,224,461	$ 3,612,463
Prime contractor
Disaggregation Of Revenue [Line Items]
Revenue	1,344,315	1,153,599	3,849,561	3,335,427
Subcontractor
Disaggregation Of Revenue [Line Items]
Revenue	121,285	111,359	374,900	277,036
Department of Defense
Disaggregation Of Revenue [Line Items]
Revenue	1,037,242	887,030	2,965,263	2,540,093
Federal civilian agencies
Disaggregation Of Revenue [Line Items]
Revenue	361,320	318,374	1,067,342	898,491
Commercial and other
Disaggregation Of Revenue [Line Items]
Revenue	67,038	59,554	191,856	173,879
Cost-plus-fee
Disaggregation Of Revenue [Line Items]
Revenue	852,700	704,627	2,418,891	2,003,204
Firm fixed-price
Disaggregation Of Revenue [Line Items]
Revenue	405,736	374,006	1,212,579	1,055,384
Time and materials
Disaggregation Of Revenue [Line Items]
Revenue	207,164	186,325	592,991	553,875
Domestic
Disaggregation Of Revenue [Line Items]
Revenue	1,419,358	1,225,531	4,097,924	3,494,606
Domestic | Prime contractor
Disaggregation Of Revenue [Line Items]
Revenue	1,298,073	1,114,172	3,723,024	3,217,570
Domestic | Subcontractor
Disaggregation Of Revenue [Line Items]
Revenue	121,285	111,359	374,900	277,036
Domestic | Department of Defense
Disaggregation Of Revenue [Line Items]
Revenue	1,037,242	887,030	2,965,263	2,540,093
Domestic | Federal civilian agencies
Disaggregation Of Revenue [Line Items]
Revenue	361,320	318,374	1,067,342	898,491
Domestic | Commercial and other
Disaggregation Of Revenue [Line Items]
Revenue	20,796	20,127	65,319	56,022
Domestic | Cost-plus-fee
Disaggregation Of Revenue [Line Items]
Revenue	852,700	704,627	2,418,891	2,003,204
Domestic | Firm fixed-price
Disaggregation Of Revenue [Line Items]
Revenue	376,314	348,143	1,128,866	982,232
Domestic | Time and materials
Disaggregation Of Revenue [Line Items]
Revenue	190,344	172,761	550,167	509,170
International
Disaggregation Of Revenue [Line Items]
Revenue	46,242	39,427	126,537	117,857
International | Prime contractor
Disaggregation Of Revenue [Line Items]
Revenue	46,242	39,427	126,537	117,857
International | Commercial and other
Disaggregation Of Revenue [Line Items]
Revenue	46,242	39,427	126,537	117,857
International | Firm fixed-price
Disaggregation Of Revenue [Line Items]
Revenue	29,422	25,863	83,713	73,152
International | Time and materials
Disaggregation Of Revenue [Line Items]
Revenue	$ 16,820	$ 13,564	$ 42,824	$ 44,705