Revenue Recognition (Tables)

6 Months Ended

Jun. 30, 2021

Revenue From Contract With Customer [Abstract]

Disaggregation of Revenue

Disaggregation of Revenue

Changes in the three and six months ended June 30, 2021 compared to the three and six months ended June 30, 2020 were driven by an increase of revenue in the energy, environment, and infrastructure client market, primarily led by revenue from international government clients, an increase in the health, education, and social programs client market led by revenue from U.S. federal government and international government clients, and an increase in the consumer and financial services client market led by revenue from commercial clients. Revenue from safety and security client market saw a slight decrease in the three months ended June 30, 2021 compared to 2020, mainly from U.S. federal government clients, and a slight increase in the six months ended June 30, 2021 compared to 2020, mainly from international government clients.

	Three Months Ended June 30,										Six Months Ended June 30,
	2021					2020					2021					2020
	Dollars		Percent			Dollars		Percent			Dollars		Percent			Dollars		Percent
Client Markets:
Energy, environment, and infrastructure	$	168,230		43	%	$	150,234		42	%	$	332,510		43	%	$	299,050		42	%
Health, education, and social programs		167,319		43	%		152,036		43	%		325,255		42	%		303,388		43	%
Safety and security		29,618		7	%		30,086		9	%		60,816		8	%		60,403		8	%
Consumer and financial services		27,358		7	%		21,631		6	%		52,422		7	%		49,384		7	%
Total	$	392,525		100	%	$	353,987		100	%	$	771,003		100	%	$	712,225		100	%

	Three Months Ended June 30,										Six Months Ended June 30,
	2021					2020					2021					2020
	Dollars		Percent			Dollars		Percent			Dollars		Percent			Dollars		Percent
Client Type:
U.S. federal government	$	182,188		46	%	$	170,786		48	%	$	358,100		46	%	$	326,389		46	%
U.S. state and local government		58,058		15	%		57,388		16	%		114,961		15	%		118,280		16	%
International government		37,801		10	%		17,858		5	%		74,925		10	%		40,667		6	%
Total Government		278,047		71	%		246,032		69	%		547,986		71	%		485,336		68	%
Commercial		114,478		29	%		107,955		31	%		223,017		29	%		226,889		32	%
Total	$	392,525		100	%	$	353,987		100	%	$	771,003		100	%	$	712,225		100	%

	Three Months Ended June 30,										Six Months Ended June 30,
	2021					2020					2021					2020
	Dollars		Percent			Dollars		Percent			Dollars		Percent			Dollars		Percent
Contract Mix:
Time-and-materials	$	162,368		41	%	$	168,371		48	%	$	322,146		42	%	$	336,521		47	%
Fixed price		160,169		41	%		124,141		35	%		307,696		40	%		257,265		36	%
Cost-based		69,988		18	%		61,475		17	%		141,161		18	%		118,439		17	%
Total	$	392,525		100	%	$	353,987		100	%	$	771,003		100	%	$	712,225		100	%

Schedule of Contract Balances and Changes in Contract Balances

Contract Balances:

Contract assets consist primarily of unbilled amounts resulting from long-term contracts when revenue recognized exceeds the amount billed often due to billing schedule timing. Contract liabilities result from advance payments received on a contract or from billings in excess of revenue recognized on long-term contracts due to billing schedule timing.

The following table summarizes the contract balances as of June 30, 2021 and December 31, 2020:

	June 30, 2021			December 31, 2020			$ Change		% Change
Contract assets	$	150,390		$	143,369		$	7,021		4.9	%
Contract liabilities		(35,700	)		(42,050	)		6,350		(15.1	%)
Net contract assets (liabilities)	$	114,690		$	101,319		$	13,371		13.2	%