Quarterly report pursuant to Section 13 or 15(d)

Commitments and Contingencies- Commitments as a Result of Acquisitions (Details)

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Commitments and Contingencies- Commitments as a Result of Acquisitions (Details)
 9 Months Ended
Sep. 30, 2018
USD ($)
project
Dec. 31, 2017
USD ($)
Jun. 30, 2014
GBP (£)
Loss Contingencies [Line Items]      
Number of projects acquired | project 2    
EEX      
Loss Contingencies [Line Items]      
Business combination, contingent consideration arrangements, range of outcomes, value, high (up to) $ 5,861,000   £ 4,500,000
Contingent consideration, liability 0 $ 0  
Undisclosed Name of Acquiree 1      
Loss Contingencies [Line Items]      
Contingent consideration, liability, certain acquired receivables $ 425,000    
Contingent consideration, liability, acquired receivables, payment period 15 months    
Undisclosed Name of Acquiree 2      
Loss Contingencies [Line Items]      
Contingent consideration, liability $ 2,000,000    
Contingent consideration, liability, revenue earn-outs, payment period 5 years    
Contingent consideration, liability, revenue earn-outs $ 555,000    
Solar Projects 1      
Loss Contingencies [Line Items]      
Contingent consideration, liability $ 4,022,000    
Number of projects acquired | project 5