Contracts Receivable and Retainage (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2018 USD ($) module	Dec. 31, 2017 USD ($)
Long-term Contracts or Programs Disclosure [Line Items]
Contract receivable	$ 27,359	$ 28,466
Allowance for bad debt	$ 2,000
Customer within Fabrication Division
Long-term Contracts or Programs Disclosure [Line Items]
Number of modules with contract receivables | module	4
Contract Receivable | Customer Concentration Risk | Two Major Customers
Long-term Contracts or Programs Disclosure [Line Items]
Contract receivable	$ 18,500
Percentage of contract receivable	67.70%