Net Income (Loss) Per Share - Computation of Basic and Diluted Loss Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended			6 Months Ended	9 Months Ended	12 Months Ended
	Sep. 27, 2020	Jun. 28, 2020	Mar. 29, 2020	Jun. 28, 2020	Sep. 27, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Numerator:
Net income (loss) attributed to PAE Incorporated	$ 15,318	$ (3,446)	$ 25,984	$ 22,538	$ 37,855	$ 28,750	$ (49,809)	$ (34,459)
Denominator:
Basic weighted average shares (in shares)	92,070,306	92,044,098	59,807,549	75,890,028	81,323,258	84,114,016	21,127,823	21,127,823
Diluted weighted average shares (in shares)	93,392,565	92,787,379	59,807,549	76,273,931	82,115,825	85,369,328	21,127,823	21,127,823
Basic income (loss) per share (in dollars per share)	$ 0.17	$ (0.04)	$ 0.43	$ 0.30	$ 0.47	$ 0.34	$ (2.36)	$ (1.63)
Diluted income (loss) per share (in dollars per share)	$ 0.16	$ (0.04)	$ 0.43	$ 0.30	$ 0.46	$ 0.34	$ (2.36)	$ (1.63)