Business Combinations and Acquisitions - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands				3 Months Ended	12 Months Ended
	Nov. 23, 2020	Nov. 20, 2020	Feb. 10, 2020	Dec. 31, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Business Acquisition [Line Items]
Common stock par value (in dollars per share)				$ 0.0001	$ 0.0001	$ 0.0001
Goodwill				$ 590,668	$ 590,668	$ 409,588	$ 408,025
PE Shay Holdings, LLC
Business Acquisition [Line Items]
Post-closing adjustment, payment to management				20,200
PAE Management
Business Acquisition [Line Items]
Post-closing adjustment, payment to management				$ 1,000
Class A Common Stock
Business Acquisition [Line Items]
Common stock par value (in dollars per share)				$ 0.0001	$ 0.0001
Shay Holding Corporation Merger
Business Acquisition [Line Items]
Aggregate cash consideration paid			$ 424,200
Shay Holding Corporation Merger | Earn-Out Shares
Business Acquisition [Line Items]
Period following completion of business combination (in years)			5 years
Shay Holding Corporation Merger | Additional Paid-in Capital
Business Acquisition [Line Items]
Acquisition fees and expenses				$ 20,900	$ 20,900
Shay Holding Corporation Merger | Class A Common Stock
Business Acquisition [Line Items]
Consideration paid (in shares)			21,127,823
Shay Holding Corporation Merger | Class A Common Stock | Earn-Out Shares
Business Acquisition [Line Items]
Maximum additional earn-out (in shares)			4,000,000
CENTRA
Business Acquisition [Line Items]
Outstanding capital stock acquired (as a percent)		100.00%
Business combination, consideration transferred		$ 225,300
Goodwill		$ 125,113
Revenue recognized					31,500
Metis Solution
Business Acquisition [Line Items]
Outstanding capital stock acquired (as a percent)	100.00%
Business combination, consideration transferred	$ 95,700
Goodwill	$ 55,967
Revenue recognized					$ 7,600