Revenue Recognition (Tables)

9 Months Ended

Sep. 30, 2021

Revenue From Contract With Customer [Abstract]

Disaggregation of Revenue

Disaggregation of Revenue

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

	Three Months Ended September 30,										Nine Months Ended September 30,
	2021					2020					2021					2020
	Dollars		Percent			Dollars		Percent			Dollars		Percent			Dollars		Percent
Client Markets:
Energy, environment, and infrastructure	$	156,661		40	%	$	147,188		41	%	$	488,018		42	%	$	445,592		42	%
Health, education, and social programs		182,334		46	%		158,297		44	%		508,255		44	%		461,808		43	%
Safety and security		28,304		7	%		30,539		8	%		89,120		7	%		90,944		8	%
Consumer and financial services		26,761		7	%		24,291		7	%		79,670		7	%		74,196		7	%
Total	$	394,060		100	%	$	360,315		100	%	$	1,165,063		100	%	$	1,072,540		100	%

	Three Months Ended September 30,										Nine Months Ended September 30,
	2021					2020					2021					2020
	Dollars		Percent			Dollars		Percent			Dollars		Percent			Dollars		Percent
Client Type:
U.S. federal government	$	195,107		49	%	$	175,126		49	%	$	553,232		48	%	$	501,525		47	%
U.S. state and local government		58,516		15	%		50,819		14	%		173,451		15	%		169,001		16	%
International government		32,249		8	%		20,194		5	%		107,175		9	%		60,861		5	%
Total Government		285,872		72	%		246,139		68	%		833,858		72	%		731,387		68	%
Commercial		108,188		28	%		114,176		32	%		331,205		28	%		341,153		32	%
Total	$	394,060		100	%	$	360,315		100	%	$	1,165,063		100	%	$	1,072,540		100	%

	Three Months Ended September 30,										Nine Months Ended September 30,
	2021					2020					2021					2020
	Dollars		Percent			Dollars		Percent			Dollars		Percent			Dollars		Percent
Contract Mix:
Time-and-materials	$	157,571		40	%	$	168,250		47	%	$	479,632		41	%	$	504,772		47	%
Fixed price		166,121		42	%		135,260		37	%		473,901		41	%		392,525		37	%
Cost-based		70,368		18	%		56,805		16	%		211,530		18	%		175,243		16	%
Total	$	394,060		100	%	$	360,315		100	%	$	1,165,063		100	%	$	1,072,540		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 September 30, 2021 and December 31, 2020:

	September 30, 2021			December 31, 2020			$ Change		% Change
Contract assets	$	154,804		$	143,369		$	11,435		8.0	%
Contract liabilities		(38,108	)		(42,050	)		3,942		(9.4	%)
Net contract assets (liabilities)	$	116,696		$	101,319		$	15,377		15.2	%