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Contracts in progress (Details) - USD ($)
 12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Contract With Customer, In Progress, Revenue Recognized And Amounts Billed, Disclosure [Line Items]    
Costs and estimated earnings in excess of billings $ 1,675,781 $ 835,669
Billings in excess of costs and estimated earnings (614,386) (109,940)
Contracts in progress    
Contract With Customer, In Progress, Revenue Recognized And Amounts Billed, Disclosure [Line Items]    
Revenues recognized to date on contracts in process 24,041,993 6,377,657
Amounts billed to date on contracts in process (22,980,598) (5,651,928)
Net overbillings 1,061,395 725,729
Costs and estimated earnings in excess of billings 1,675,781 835,669
Billings in excess of costs and estimated earnings $ (614,386) $ (109,940)