Revenues from Contracts with Customers - Disaggregation of Revenue (Detail) - USD ($) $ in Thousands	3 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Disaggregation Of Revenue [Line Items]
Revenues	$ 1,490,898	$ 1,459,506
Expertise
Disaggregation Of Revenue [Line Items]
Revenues	703,046	740,683
Technology
Disaggregation Of Revenue [Line Items]
Revenues	787,852	718,823
Prime contractor
Disaggregation Of Revenue [Line Items]
Revenues	1,341,559	1,326,838
Subcontractor
Disaggregation Of Revenue [Line Items]
Revenues	149,339	132,668
Department of Defense
Disaggregation Of Revenue [Line Items]
Revenues	1,000,127	1,004,195
Federal civilian agencies
Disaggregation Of Revenue [Line Items]
Revenues	413,664	390,179
Commercial and other
Disaggregation Of Revenue [Line Items]
Revenues	77,107	65,132
Cost-plus-fee
Disaggregation Of Revenue [Line Items]
Revenues	893,713	823,609
Fixed-price
Disaggregation Of Revenue [Line Items]
Revenues	407,705	433,814
Time and materials
Disaggregation Of Revenue [Line Items]
Revenues	189,480	202,083
Domestic
Disaggregation Of Revenue [Line Items]
Revenues	1,443,722	1,418,187
Domestic | Expertise
Disaggregation Of Revenue [Line Items]
Revenues	683,624	723,197
Domestic | Technology
Disaggregation Of Revenue [Line Items]
Revenues	760,098	694,990
Domestic | Prime contractor
Disaggregation Of Revenue [Line Items]
Revenues	1,298,653	1,288,705
Domestic | Subcontractor
Disaggregation Of Revenue [Line Items]
Revenues	145,069	129,482
Domestic | Department of Defense
Disaggregation Of Revenue [Line Items]
Revenues	1,000,127	1,004,195
Domestic | Federal civilian agencies
Disaggregation Of Revenue [Line Items]
Revenues	413,664	390,179
Domestic | Commercial and other
Disaggregation Of Revenue [Line Items]
Revenues	29,931	23,813
Domestic | Cost-plus-fee
Disaggregation Of Revenue [Line Items]
Revenues	893,713	823,609
Domestic | Fixed-price
Disaggregation Of Revenue [Line Items]
Revenues	374,474	409,584
Domestic | Time and materials
Disaggregation Of Revenue [Line Items]
Revenues	175,535	184,994
International
Disaggregation Of Revenue [Line Items]
Revenues	47,176	41,319
International | Expertise
Disaggregation Of Revenue [Line Items]
Revenues	19,422	17,486
International | Technology
Disaggregation Of Revenue [Line Items]
Revenues	27,754	23,833
International | Prime contractor
Disaggregation Of Revenue [Line Items]
Revenues	42,906	38,133
International | Subcontractor
Disaggregation Of Revenue [Line Items]
Revenues	4,270	3,186
International | Commercial and other
Disaggregation Of Revenue [Line Items]
Revenues	47,176	41,319
International | Fixed-price
Disaggregation Of Revenue [Line Items]
Revenues	33,231	24,230
International | Time and materials
Disaggregation Of Revenue [Line Items]
Revenues	$ 13,945	$ 17,089