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. 11, 2020	Feb. 10, 2020	Dec. 31, 2020	Dec. 31, 2020	Sep. 27, 2020	Jun. 28, 2020	Mar. 29, 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	$ 0.0001	$ 0.0001	$ 0.0001
Goodwill					$ 590,668	$ 590,668	$ 409,588	$ 409,588	$ 409,588	$ 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
Transaction costs			$ 3,400
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			$ 18,200
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