Receivables, Net

3 Months Ended

Mar. 31, 2019

Receivables [Abstract]

Receivables, Net

8.  Receivables, net

(in thousands)	March 31, 2019		December 31, 2018		March 31, 2018
Contracts completed and in progress:
Billed	$	200,908	$	285,521	$	214,494
Unbilled		112,892		98,755		73,128
Total contracts completed and in progress		313,800		384,276		287,622
Material sales		29,948		45,286		28,233
Other		25,006		44,195		14,442
Total gross receivables		368,754		473,757		330,297
Less: allowance for doubtful accounts		539		511		105
Total net receivables	$	368,215	$	473,246	$	330,192

Receivables include billed and unbilled amounts for services provided to clients for which we have an unconditional right to payment as of the end of the applicable period and do not bear interest. Included in other receivables at March 31, 2019, December 31, 2018 and March 31, 2018 were items such as estimated recovery from back charge claims, notes receivable, fuel tax refunds and income tax refunds. No such receivables individually exceeded 10% of total net receivables at any of these dates.