Receivables, Net (Tables)

6 Months Ended

Jun. 30, 2019

Receivables [Abstract]

Summary of Receivables

(in thousands)	June 30, 2019		December 31, 2018		June 30, 2018
Contracts completed and in progress:
Billed	$	313,185	$	285,521	$	340,548
Unbilled		163,950		98,755		71,464
Total contracts completed and in progress		477,135		384,276		412,012
Material sales		61,204		45,286		64,128
Other		14,260		44,195		16,644
Total gross receivables		552,599		473,757		492,784
Less: allowance for doubtful accounts		641		511		66
Total net receivables	$	551,958	$	473,246	$	492,718