Receivables, net



(in thousands)	June 30, 2017		December 31, 2016		June 30, 2016
Construction contracts:
Completed and in progress	$	343,707	$	288,160	$	266,685
Retentions	75,891		84,878		95,415
Total construction contracts	419,598		373,038		362,100
Construction material sales	54,165		29,357		54,277
Other	10,892		17,523		15,227
Total gross receivables	484,655		419,918		431,604
Less: allowance for doubtful accounts	410		573		477
Total net receivables	$	484,245	$	419,345	$	431,127

Receivables include amounts billed and billable to clients for services provided as of the end of the applicable period and do not bear interest. To the extent costs are not contractually billable or have not been earned, such as claim recovery estimates, the associated revenue is included in costs and estimated earnings in excess of billings or billings in excess of costs and estimated earnings in the condensed consolidated balance sheets. As of June 30, 2017, December 31, 2016 and June 30, 2016, the aggregate claim recovery estimates included in these balances were approximately $10.8 million, $12.3 million and $8.1 million, respectively. Included in other receivables at June 30, 2017, December 31, 2016 and June 30, 2016 were items such as estimated recovery from back charge claims, notes receivable, fuel tax refunds, receivables from vendors and income tax refunds. No such receivables individually exceeded 10% of total net receivables at any of these dates. As of both June 30, 2017 and December 31, 2016 the estimated recovery from back charge claims included in Other receivables was $0.3 million and was $10.5 million as of June 30, 2016.

Certain construction contracts include retainage provisions. The balances billed but not paid by customers pursuant to these provisions generally become due upon completion and acceptance of the project work or products by the owners. As of June 30, 2017, December 31, 2016 and June 30, 2016, no retention receivable individually exceeded 10% of total net receivables at any of the presented dates. The majority of the retentions receivable are expected to be collected within one year and there were no retentions receivables determined to be uncollectible.