Receivables, net



(in thousands)	September 30, 2017		December 31, 2016		September 30, 2016
Construction contracts:
Completed and in progress	$	469,416	$	288,160	$	347,320
Retentions	88,650		84,878		97,385
Total construction contracts	558,066		373,038		444,705
Construction material sales	58,920		29,357		50,768
Other	10,412		17,523		17,760
Total gross receivables	627,398		419,918		513,233
Less: allowance for doubtful accounts	317		573		481
Total net receivables	$	627,081	$	419,345	$	512,752

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, including 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 September 30, 2017, December 31, 2016 and September 30, 2016, the aggregate claim recovery estimates included in these balances were approximately $21.6 million, $12.3 million and $7.8 million, respectively. Included in other receivables at September 30, 2017, December 31, 2016 and September 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 September 30, 2017, December 31, 2016 and September 30, 2016, the estimated recovery from back charge claims included in Other receivables was $0.3 million, $0.3 million and $9.3 million, respectively.

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 September 30, 2017, December 31, 2016 and September 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.