Investments in and Advances to Joint Ventures - Summary of Financial Information for Consolidated Joint Ventures (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Dec. 31, 2024	Mar. 31, 2024	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Schedule Of Equity Method Investments [Line Items]
Current assets	$ 2,462,400		$ 2,462,400	$ 2,137,526
Total assets	5,487,962		5,487,962	4,804,061
Current liabilities	1,915,644		1,915,644	1,410,884
Total liabilities	2,953,473		2,953,473	2,427,346
Total joint venture equity	2,416,389		2,416,389	2,287,211
Revenue	1,734,317	$ 1,535,676	6,750,576	5,442,749	$ 4,195,272
Costs			5,344,154	4,236,735	3,248,550
Net income attributable to Parsons Corporation	54,180	$ 39,750	235,053	161,149	96,664
Net income attributable to noncontrolling interests			55,612	46,766	29,901
Consolidated Joint Ventures
Schedule Of Equity Method Investments [Line Items]
Current assets	519,450		519,450	426,633
Noncurrent assets	9,841		9,841	14,295
Total assets	529,291		529,291	440,928
Current liabilities	296,774		296,774	260,286
Noncurrent liabilities	2,203		2,203	5,132
Total liabilities	298,977		298,977	265,418
Total joint venture equity	$ 230,314		230,314	175,510
Revenue			788,702	708,391	483,888
Costs			676,258	613,186	422,559
Net income attributable to Parsons Corporation			112,444	95,205	61,329
Net income attributable to noncontrolling interests			$ 55,612	$ 46,766	$ 29,901