Costs and Estimated Earnings on Uncompleted Contracts (Details) - USD ($)	Jun. 30, 2018	Dec. 31, 2017
Costs and estimated earnings on uncompleted contracts
Costs incurred on uncompleted contracts	$ 7,267,669	$ 3,681,965
Estimated earnings to date on uncompleted contracts	(494,749)	328,273
Gross contract assets (liabilities)	7,762,418	4,010,238
Less: billings to date	(8,456,494)	(5,622,111)
Net contract assets (liabilities)	$ (694,076)	$ (1,611,873)

Costs incurred on uncompleted contracts.

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- Definition

Estimated income loss on uncompleted contracts.

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Amount billed to customers under long-term contracts or programs but not paid. Excludes amounts due that have been withheld because of retainage provisions in a contract.

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Amount billed to customers under long-term contracts or programs that have been withheld because of retainage provisions in a contract.

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Amount of receivable reflecting the cost incurred on uncompleted contracts in excess of related billings.

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