Investments in and Advances to Joint Ventures - Summary of Financial Information for Unconsolidated Joint Ventures (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Schedule Of Equity Method Investments [Line Items]
Current assets	$ 1,601,972		$ 1,526,409
Total assets	3,488,605		3,450,368
Current liabilities	1,151,324		1,144,382
Total liabilities	1,821,226		1,789,612
Total joint venture equity	1,635,262		1,629,890
Investments in and advances to unconsolidated joint ventures	65,716		68,620
Revenue	970,993	$ 904,405
Costs	769,632	714,237
Net income attributable to Parsons Corporation	12,973	9,741
Equity in earnings of unconsolidated joint ventures	6,114	10,397
Unconsolidated Joint Ventures
Schedule Of Equity Method Investments [Line Items]
Current assets	735,279		801,335
Noncurrent assets	527,529		564,160
Total assets	1,262,808		1,365,495
Current liabilities	663,622		655,495
Noncurrent liabilities	475,463		507,131
Total liabilities	1,139,085		1,162,626
Total joint venture equity	123,723		202,869
Investments in and advances to unconsolidated joint ventures	65,716		$ 68,620
Revenue	238,188	229,466
Costs	223,686	216,780
Net income attributable to Parsons Corporation	14,502	12,686
Equity in earnings of unconsolidated joint ventures	$ 6,114	$ 10,397