Receivables, Net (Tables)

3 Months Ended

Mar. 31, 2019

Receivables [Abstract]

Summary of Receivables

(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