Earnings Per Share - Net Income Available to Shareholders to Compute Basic and Diluted EPS (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Earnings Per Share [Abstract]
Net income attributable to Parsons Corporation	$ 6,702	$ 23,299	$ 15,741	$ 36,272
Convertible senior notes if-converted method interest adjustment	531		1,059
Diluted net income attributable to Parsons Corporation	$ 7,233	$ 23,299	$ 16,800	$ 36,272