The Company disaggregates revenue from clients, most of which is earned over time, into categories that depict how the nature, amount and uncertainty of revenue and cash flows are affected by economic factors. Those categories are client market, client type and contract mix. Client market revenue information provides insight into the breadth of the Company’s expertise. In classifying revenue by client market, the Company attributes revenue from a client to the market that the Company believes is the client’s primary market. The Company also classifies revenue by the type of entity for which it does business, which is an indicator of the diversity of its client base. The Company attributes revenue generated from being a subcontractor to a commercial company as government revenue when the ultimate client is a government agency or department. Finally, disaggregation by contract mix provides insight in terms of the degree of performance risk that the Company has assumed. Fixed-price contracts are considered to provide the highest amount of performance risk as the Company is required to deliver a scope of work or level of effort for a negotiated fixed price. Time-and-materials contracts require the Company to provide skilled employees on contracts for negotiated fixed hourly rates. Since the Company is not required to deliver a scope of work, but merely skilled employees, it considers these contracts to be less risky than a fixed-price agreement. Cost-based contracts are considered to provide the lowest amount of performance risk since the Company is generally reimbursed for all contract costs incurred in performance of contract deliverables with only the amount of incentive or award fees (if applicable) dependent on the achievement of negotiated performance requirements.

Increases in revenue from energy, environment, and infrastructure client markets, and U.S. state and local governments in the three and six months ended June 30, 2019 compared to the prior year period were primarily due to work performed on disaster recovery and relief efforts which also caused an increase in revenue generated through time-and-materials contracts. Consumer and financial services client market revenue increased primarily due to acquisitions during the prior year.

	Three Months Ended June 30,										Six Months Ended June 30,
	2019					2018					2019					2018
	Dollars		Percent			Dollars		Percent			Dollars		Percent			Dollars		Percent
Client Markets:
Energy, environment, and infrastructure	$	166,998		46	%	$	133,276		41	%	$	320,988		46	%	$	257,526		41	%
Health, education, and social programs		133,919		36	%		131,141		41	%		255,057		36	%		254,069		41	%
Safety and security		29,818		8	%		27,491		8	%		59,047		8	%		52,966		8	%
Consumer and financial services		35,982		10	%		32,407		10	%		72,879		10	%		62,534		10	%
Total	$	366,717		100	%	$	324,315		100	%	$	707,971		100	%	$	627,095		100	%

	Three Months Ended										Six Months Ended June 30,
	June 30, 2019					June 30, 2018					2019					2018
	Dollars		Percent			Dollars		Percent			Dollars		Percent			Dollars		Percent
Client Type:
U.S. federal government	$	141,193		38	%	$	139,517		43	%	$	273,363		39	%	$	273,750		44	%
U.S. state and local government		72,893		20	%		34,532		11	%		138,400		19	%		65,889		10	%
International government		31,652		9	%		34,615		11	%		58,865		8	%		63,383		10	%
Total Government		245,738		67	%		208,664		65	%		470,628		66	%		403,022		64	%
Commercial		120,979		33	%		115,651		35	%		237,343		34	%		224,073		36	%
Total	$	366,717		100	%	$	324,315		100	%	$	707,971		100	%	$	627,095		100	%

	Three Months Ended										Six Months Ended June 30,
	June 30, 2019					June 30, 2018					2019					2018
	Dollars		Percent			Dollars		Percent			Dollars		Percent			Dollars		Percent
Contract Mix:
Time-and-materials	$	167,457		46	%	$	128,103		39	%	$	323,459		46	%	$	252,290		40	%
Fixed price		146,516		40	%		136,220		42	%		280,119		40	%		258,609		41	%
Cost-based		52,744		14	%		59,992		19	%		104,393		14	%		116,196		19	%
Total	$	366,717		100	%	$	324,315		100	%	$	707,971		100	%	$	627,095		100	%

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 net contact assets (liabilities) increased $15.3 million due primarily to increases in contract assets and by a slight decrease in contract liabilities. The increase in contract assets is primarily due to hurricane relief and rebuild work for U.S. state and local governments, which is considered part of the energy, environment and infrastructure client market, and most of which has been performed on time-and-materials agreements. There were no material changes to contract balances due to impairments or business combinations during the period.

	June 30, 2019			December 31, 2018			$ Change		% Change
Contract assets	$	141,960		$	126,688		$	15,272		12.1	%
Contract liabilities		(33,435	)		(33,494	)		59		(0.2	%)
Net contract assets (liabilities)	$	108,525		$	93,194		$	15,331		16.5	%

The Company had $1.5 billion in unfulfilled performance obligations as of June 30, 2019, which primarily entail the future delivery of services for which revenue will be recognized over time. The obligations relate to continued or additional services required on contracts and were generally valued using an estimated cost plus margin approach, with variable consideration being estimated at the most likely amount. The Company expects to satisfy these performance obligations, on average, in one to two years.