

	As of June 30,		As of December 31,
(in thousands)	2019		2018
Retainage receivable	$	508,423	$	478,744
Costs and estimated earnings in excess of billings:
Claims		752,712		698,274
Unapproved change orders		334,774		354,000
Other unbilled costs and profits		77,922		90,021
Total costs and estimated earnings in excess of billings		1,165,408		1,142,295
Capitalized contract costs		61,376		37,404
Total contract assets	$	1,735,207	$	1,658,443

Retainage receivable represents amounts invoiced to customers where payments have been partially withheld pending the completion of certain milestones, satisfaction of other contractual conditions or the completion of the project. Retainage agreements vary from project to project and balances could be outstanding for several months or years depending on a number of circumstances such as contract-specific terms, project performance and other variables that may arise as the Company makes progress towards completion.

Costs and estimated earnings in excess of billings represent the excess of contract costs and profits (or contract revenue) over the amount of contract billings to date and are classified as a current asset. Costs and estimated earnings in excess of billings result when either: 1) the appropriate contract revenue amount has been recognized over time in accordance with ASC 606, Revenue from Contracts with Customers (“ASC 606”), but a portion of the revenue recorded cannot be billed currently due to the billing terms defined in the contract, or 2) costs are incurred related to certain claims and unapproved change orders. Claims occur when there is a dispute regarding both a change in the scope of work and the price associated with that change. Unapproved change orders occur when a change in the scope of work results in additional work being performed before the parties have agreed on the corresponding change in the contract price. The Company routinely estimates recovery related to claims and unapproved change orders as a form of variable consideration at the most likely amount it expects to receive and to the extent it is probable that a significant reversal of cumulative revenue recognized will not occur when the uncertainty associated with the variable consideration is resolved. Claims and unapproved change orders are billable upon the agreement and resolution between the contractual parties and after the execution of contractual amendments. Increases in claims and unapproved change orders typically result from costs being incurred against existing or new positions; decreases normally result from resolutions and subsequent billings. As discussed in Note 11, Commitments and Contingencies, the resolution of these claims and unapproved change orders may require litigation or other forms of dispute resolution proceedings. Other unbilled costs and profits are billable in accordance with the billing terms of each of the existing contractual arrangements and, as such, the timing of contract billing cycles can cause fluctuations in the balance of unbilled costs and profits. Ultimate resolution of other unbilled costs and profits typically involves incremental progress toward contractual requirements or milestones.

Capitalized contract costs primarily represent costs to fulfill a contract that (1) directly relate to an existing or anticipated contract, (2) generate or enhance resources that will be used in satisfying performance obligations in the future and (3) are expected to be recovered through the contract, and are included in other current assets. Capitalized contract costs are generally expensed to the associated contract over the period of anticipated use on the project. During the three and six months ended June 30, 2019, $8.6 million and $14.3 million, respectively, of previously capitalized contract costs were amortized and recognized as expense on the related contracts. During the three and six months ended June 30, 2018, $4.1 million and $8.2 million, respectively, of previously capitalized contract costs were amortized and recognized as expense on the related contracts.

Contract liabilities include amounts owed under retainage provisions and billings in excess of costs and estimated earnings. The amount as reported on the Condensed Consolidated Balance Sheets consisted of the following:



	As of June 30,		As of December 31,
(in thousands)	2019		2018
Retainage payable	$	227,884	$	211,956
Billings in excess of costs and estimated earnings		635,924		573,190
Total contract liabilities	$	863,808	$	785,146