Segment Information - Summary of Revenues by Business Lines (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Segment Reporting Information [Line Items]
Revenues	$ 879,356	$ 979,459	$ 1,754,053	$ 1,950,452
Federal Solution Segment
Segment Reporting Information [Line Items]
Revenues	442,675	482,210	894,744	959,781
Federal Solution Segment | Cyber & Intelligence
Segment Reporting Information [Line Items]
Revenues	85,282	102,993	168,610	201,875
Federal Solution Segment | Space & Geospatial Solutions
Segment Reporting Information [Line Items]
Revenues	77,614	57,967	160,673	109,255
Federal Solution Segment | Missile Defense & C5ISR
Segment Reporting Information [Line Items]
Revenues	145,493	154,767	290,208	309,336
Federal Solution Segment | Engineered Systems
Segment Reporting Information [Line Items]
Revenues	134,286	166,483	275,253	339,315
Critical Infrastructure
Segment Reporting Information [Line Items]
Revenues	436,681	497,249	859,309	990,671
Critical Infrastructure | Connected Communities
Segment Reporting Information [Line Items]
Revenues	81,321	98,359	171,204	200,260
Critical Infrastructure | Mobility Solutions
Segment Reporting Information [Line Items]
Revenues	$ 355,360	$ 398,890	$ 688,105	$ 790,411