Revenue Recognition - Disaggregation of Revenue by Contract Type, Customer Information and Prime or Subcontractor (Detail) - USD ($) $ in Thousands	3 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Disaggregation Of Revenue [Line Items]
Revenue	$ 1,459,506	$ 1,363,392
Expertise
Disaggregation Of Revenue [Line Items]
Revenue	740,683	722,353
Technology
Disaggregation Of Revenue [Line Items]
Revenue	718,823	641,039
Prime contractor
Disaggregation Of Revenue [Line Items]
Revenue	1,326,838	1,235,105
Subcontractor
Disaggregation Of Revenue [Line Items]
Revenue	132,668	128,287
Department of Defense
Disaggregation Of Revenue [Line Items]
Revenue	1,004,195	937,640
Federal civilian agencies
Disaggregation Of Revenue [Line Items]
Revenue	390,179	363,993
Commercial and other
Disaggregation Of Revenue [Line Items]
Revenue	65,132	61,759
Cost-plus-fee
Disaggregation Of Revenue [Line Items]
Revenue	823,609	747,714
Fixed-price
Disaggregation Of Revenue [Line Items]
Revenue	433,814	417,976
Time and materials
Disaggregation Of Revenue [Line Items]
Revenue	202,083	197,702
Domestic
Disaggregation Of Revenue [Line Items]
Revenue	1,418,187	1,324,773
Domestic | Expertise
Disaggregation Of Revenue [Line Items]
Revenue	723,197	709,025
Domestic | Technology
Disaggregation Of Revenue [Line Items]
Revenue	694,990	615,748
Domestic | Prime contractor
Disaggregation Of Revenue [Line Items]
Revenue	1,288,705	1,197,634
Domestic | Subcontractor
Disaggregation Of Revenue [Line Items]
Revenue	129,482	127,139
Domestic | Department of Defense
Disaggregation Of Revenue [Line Items]
Revenue	1,004,195	937,640
Domestic | Federal civilian agencies
Disaggregation Of Revenue [Line Items]
Revenue	390,179	363,993
Domestic | Commercial and other
Disaggregation Of Revenue [Line Items]
Revenue	23,813	23,140
Domestic | Cost-plus-fee
Disaggregation Of Revenue [Line Items]
Revenue	823,609	747,714
Domestic | Fixed-price
Disaggregation Of Revenue [Line Items]
Revenue	409,584	391,536
Domestic | Time and materials
Disaggregation Of Revenue [Line Items]
Revenue	184,994	185,523
International
Disaggregation Of Revenue [Line Items]
Revenue	41,319	38,619
International | Expertise
Disaggregation Of Revenue [Line Items]
Revenue	17,486	13,328
International | Technology
Disaggregation Of Revenue [Line Items]
Revenue	23,833	25,291
International | Prime contractor
Disaggregation Of Revenue [Line Items]
Revenue	38,133	37,471
International | Subcontractor
Disaggregation Of Revenue [Line Items]
Revenue	3,186	1,148
International | Commercial and other
Disaggregation Of Revenue [Line Items]
Revenue	41,319	38,619
International | Fixed-price
Disaggregation Of Revenue [Line Items]
Revenue	24,230	26,440
International | Time and materials
Disaggregation Of Revenue [Line Items]
Revenue	$ 17,089	$ 12,179