Annual report pursuant to Section 13 and 15(d)

Business Segment, Business Credit Risks and Concentration - Business Concentration and Credit Risks (Details)

v3.19.1
Business Segment, Business Credit Risks and Concentration - Business Concentration and Credit Risks (Details) - USD ($)
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Concentration Risk [Line Items]    
Accounts receivable and accrued billings, net $ 22,236,071 $ 21,566,842
Revenue | Major customers | Customer A    
Concentration Risk [Line Items]    
Revenues $ 39,866,000 $ 38,306,000
Concentration risk, percentage 29.00% 34.00%
Revenue | Major customers | Customer B    
Concentration Risk [Line Items]    
Revenues $ 22,085,000 $ 16,912,000
Concentration risk, percentage 16.00% 15.00%
Revenue | Major customers | Customer C    
Concentration Risk [Line Items]    
Revenues $ 16,972,000 $ 11,681,000
Concentration risk, percentage 12.00% 10.00%
Revenue | Service/product    
Concentration Risk [Line Items]    
Revenues $ 138,149,000 $ 113,953,000
Concentration risk, percentage 100.07% 100.00%
Revenue | Service/product | Electrical construction    
Concentration Risk [Line Items]    
Revenues $ 136,527,000 $ 109,154,000
Concentration risk, percentage 99.00% 96.00%
Revenue | Service/product | Principal electrical construction operations    
Concentration Risk [Line Items]    
Revenues $ 129,022,000 $ 100,604,000
Concentration risk, percentage 93.00% 88.00%
Revenue | Service/product | Other electrical construction    
Concentration Risk [Line Items]    
Revenues $ 7,505,000 $ 8,550,000
Concentration risk, percentage 6.00% 8.00%
Revenue | Service/product | Real estate development    
Concentration Risk [Line Items]    
Revenues $ 1,622,000 $ 4,799,000
Concentration risk, percentage 1.00% 4.00%