Consolidated Statements of Shareholder's Equity (Unaudited) - USD ($) $ in Thousands	Total	Revision of Prior Period, Accounting Standards Update, Adjustment	Common Stock	Treasury Stock	Additional Paid-in Capital	Additional Paid-in Capital Revision of Prior Period, Accounting Standards Update, Adjustment	Retained Earnings (Accumulated Deficit)	Retained Earnings (Accumulated Deficit) Revision of Prior Period, Accounting Standards Update, Adjustment	Accumulated Other Comprehensive Income (Loss)	Total Parsons Equity	Total Parsons Equity Revision of Prior Period, Accounting Standards Update, Adjustment	Noncontrolling Interest
Beginning balance at Dec. 31, 2019	$ 1,660,756		$ 146,441	$ (934,240)	$ 2,649,975		$ (218,025)		$ (14,261)	$ 1,629,890		$ 30,866
Beginning balance (ASU 2016-13) at Dec. 31, 2019		$ (1,000)						$ (1,000)			$ (1,000)
Comprehensive income
Net income	45,496						36,272			36,272		9,224
Foreign currency translation gain (loss), net	(5,696)								(5,692)	(5,692)		(4)
Pension adjustments, net	(38)								(38)	(38)
Contributions	223											223
Distributions	(1,605)											(1,605)
Issuance of equity securities, net of retirements	1,684		55		1,629					1,684
Stock-based compensation	6,432				6,432					6,432
Ending Balance at Jun. 30, 2020	1,706,252		146,496	(934,240)	2,658,036		(182,753)		(19,991)	1,667,548		38,704
Beginning balance at Mar. 31, 2020	1,667,379		146,441	(934,240)	2,652,227		(206,052)		(23,114)	1,635,262		32,117
Comprehensive income
Net income	31,125						23,299			23,299		7,826
Foreign currency translation gain (loss), net	3,104								3,100	3,100		4
Pension adjustments, net	23								23	23
Contributions	2											2
Distributions	(1,245)											(1,245)
Issuance of equity securities, net of retirements	1,684		55		1,629					1,684
Stock-based compensation	4,180				4,180					4,180
Ending Balance at Jun. 30, 2020	1,706,252		146,496	(934,240)	2,658,036		(182,753)		(19,991)	1,667,548		38,704
Beginning balance at Dec. 31, 2020	1,861,417		146,609	(899,328)	2,700,925		(120,569)		(13,865)	1,813,772		47,645
Beginning balance (ASU 2020-06) at Dec. 31, 2020		$ (37,220)				$ (40,002)		$ 2,782			$ (37,220)
Comprehensive income
Net income	26,041						15,741			15,741		10,300
Foreign currency translation gain (loss), net	7,926								7,922	7,922		4
Pension adjustments, net	38								38	38
Contributions	872											872
Distributions	(21,836)											(21,836)
Issuance of equity securities, net of retirements	1,851		143		1,681		27			1,851
Stock-based compensation	11,361				11,361					11,361
Ending Balance at Jun. 30, 2021	1,850,450		146,752	(899,328)	2,673,965		(102,019)		(5,905)	1,813,465		36,985
Beginning balance at Mar. 31, 2021	1,840,442		146,654	(899,328)	2,667,130		(108,720)		(8,937)	1,796,799		43,643
Comprehensive income
Net income	12,027						6,702			6,702		5,325
Foreign currency translation gain (loss), net	3,012								3,013	3,013		(1)
Pension adjustments, net	19								19	19
Contributions	865											865
Distributions	(12,847)											(12,847)
Issuance of equity securities, net of retirements	2,777		98		2,680		(1)			2,777
Stock-based compensation	4,155				4,155					4,155
Ending Balance at Jun. 30, 2021	$ 1,850,450		$ 146,752	$ (899,328)	$ 2,673,965		$ (102,019)		$ (5,905)	$ 1,813,465		$ 36,985