Investments in and Advances to Joint Ventures - Summary of Financial Information for Consolidated Joint Ventures (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Schedule Of Equity Method Investments [Line Items]
Current assets	$ 1,794,406		$ 1,794,406		$ 1,843,130
Total assets	3,839,297		3,839,297		3,937,704
Current liabilities	1,077,424		1,077,424		1,187,409
Total liabilities	1,988,847		1,988,847		2,076,287
Total joint venture equity	1,813,465		1,813,465		1,813,772
Revenue	879,356	$ 979,459	1,754,053	$ 1,950,452
Costs	680,328	749,324	1,349,410	1,518,956
Net income attributable to Parsons Corporation	6,702	23,299	15,741	36,272
Net income attributable to noncontrolling interests	5,325	7,826	10,300	9,224
Consolidated Joint Ventures
Schedule Of Equity Method Investments [Line Items]
Current assets	263,051		263,051		292,407
Noncurrent assets	2,641		2,641		2,990
Total assets	265,692		265,692		295,397
Current liabilities	191,223		191,223		201,270
Total liabilities	191,223		191,223		201,270
Total joint venture equity	74,469		74,469		$ 94,127
Revenue	98,245	117,889	194,869	218,167
Costs	87,097	101,935	173,403	199,085
Net income attributable to Parsons Corporation	11,148	15,954	21,466	19,082
Net income attributable to noncontrolling interests	$ 5,325	$ 7,826	$ 10,300	$ 9,224