Annual report pursuant to Section 13 and 15(d)

Business Acquisitions and Related Transactions - Additional Information (Details)

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Business Acquisitions and Related Transactions - Additional Information (Details)
 1 Months Ended 12 Months Ended
Jan. 31, 2019
USD ($)
Jan. 31, 2017
USD ($)
project
Dec. 31, 2019
USD ($)
developer
project
Dec. 31, 2018
USD ($)
developer
project
Dec. 30, 2018
USD ($)
Business Acquisition [Line Items]          
Fair value of consideration     $ 13,902,000    
Initial cash payment       $ 366,000  
Measurement period adjustment, recorded as a reduction to goodwill     630,000    
Measurement period adjustment, hold back contingency     398,000    
Contingent consideration liabilities     1,178,000    
Loss on change in fair value     $ 79,000 $ 44,000  
Number of projects acquired | project     10    
Number of developers current year solar projects were purchased from | developer     2 2  
Massachusetts Based Solar Operations And Maintenance Firm          
Business Acquisition [Line Items]          
Fair value of consideration $ 1,294,000        
Undisclosed Name of Acquiree One          
Business Acquisition [Line Items]          
Fair value of consideration       $ 2,326,000  
Initial cash payment       $ 1,901,000  
Contingent consideration, liability, acquired receivables, payment period       15 months  
Debt assumed       $ 0  
Measurement period adjustment, recorded as a reduction to goodwill       197,000  
Undisclosed Name of Acquiree Two          
Business Acquisition [Line Items]          
Initial cash payment       1,691,000  
Debt assumed       0  
Contingent consideration liabilities       $ 2,000,000  
Contingent consideration, liability, revenue targets, period       5 years  
Contingent consideration, liability, fair value     $ 678,000 $ 599,000 $ 555,000
Solar PV project          
Business Acquisition [Line Items]          
Initial cash payment   $ 2,409,000      
Debt assumed   $ 5,635,000      
Number of projects acquired | project   2      
Solar Projects 2018          
Business Acquisition [Line Items]          
Fair value of consideration       72,921,000  
Initial cash payment       62,116,000  
Contingent consideration liabilities       $ 5,437,000  
Number of projects acquired | project     9 12  
Number of developers current year solar projects were purchased from | developer       2  
Number of projects actually acquired under definitive agreement | project     3    
Number of projects no longer to be acquired | project     1    
Minimum          
Business Acquisition [Line Items]          
Intangible assets amortization period     1 year    
Maximum          
Business Acquisition [Line Items]          
Intangible assets amortization period     15 years    
U.S. Federal          
Business Acquisition [Line Items]          
Measurement period adjustment, recorded as a reduction to goodwill     $ 628,000    
Scenario, Plan | Solar Projects 2018          
Business Acquisition [Line Items]          
Number of projects acquired | project       6