Revenue Recognition (Tables)

12 Months Ended

Dec. 31, 2023

Revenue from Contract with Customer [Abstract]

Disaggregation of Revenue

The Company's revenue by client markets, type, and contract mix are in the following tables. Certain immaterial revenue amounts in the prior years have been reclassified due to minor adjustments and reclassification.

	Year ended December 31,
	2023		2022		2021
Client Markets:
Energy, environment, infrastructure, and disaster recovery	$	806,482	$	714,628	$	693,572
Health and social programs		814,454		704,465		563,590
Security and other civilian & commercial		342,302		360,871		295,886
Total	$	1,963,238	$	1,779,964	$	1,553,048

	Year ended December 31,
	2023		2022		2021
Client Type:
U.S. federal government	$	1,084,043	$	980,746	$	735,032
U.S. state and local government		308,134		259,764		235,416
International government		103,399		103,609		139,229
Total Government		1,495,576		1,344,119		1,109,677
Commercial		467,662		435,845		443,371
Total	$	1,963,238	$	1,779,964	$	1,553,048

	Year ended December 31,
	2023		2022		2021
Contract Mix:
Time-and-materials	$	812,430	$	713,693	$	633,135
Fixed-price		885,465		802,568		645,809
Cost-based		265,343		263,703		274,104
Total	$	1,963,238	$	1,779,964	$	1,553,048

Schedule of Contract Assets and Liabilities and Changes in Contract Balances

Contract Assets and Liabilities:

Contract assets consist of unbilled receivables on contracts where revenue recognized exceeds the amount billed. Contract liabilities result from advance payments received on a contract or from billings in excess of revenue recognized on long-term contracts.

The following table summarizes the contract balances as of December 31, 2023 and December 31, 2022:

	December 31, 2023			December 31, 2022			Change
Contract assets	$	201,832		$	169,088		$	32,744
Contract liabilities		(21,997	)		(25,773	)		3,776
Net contract assets (liabilities)	$	179,835		$	143,315		$	36,520

The net contract assets (liabilities) as of December 31, 2023 increased by $36.5 million as compared to December 31, 2022, primarily due to the timing difference between the performance of services and billings to and payments from customers. There were no material changes to contract balances due to impairments or credit losses during the period. During the years ended December 31, 2023 and 2022, the Company recognized $17.8 million and $27.4 million in revenue related to the contract liabilities balance at December 31, 2022 and 2021, respectively.

Unfulfilled