Quarterly report pursuant to Section 13 or 15(d)

Goodwill and Intangible Assets - Goodwill (Details)

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Goodwill and Intangible Assets - Goodwill (Details) - USD ($)
$ in Thousands
 9 Months Ended
Sep. 30, 2018
Dec. 31, 2017
Goodwill [Roll Forward]    
Balance, December 31, 2017 $ 56,135  
Goodwill acquired during the year 3,042  
Currency effects (324)  
Balance, September 30, 2018 58,853  
Accumulated goodwill impairment (1,016) $ (1,016)
Operating Segments | U.S. Regions    
Goodwill [Roll Forward]    
Balance, December 31, 2017 24,759  
Goodwill acquired during the year 1,611  
Currency effects 0  
Balance, September 30, 2018 26,370  
Accumulated goodwill impairment 0 0
Operating Segments | U.S. Federal    
Goodwill [Roll Forward]    
Balance, December 31, 2017 3,375  
Goodwill acquired during the year 1,431  
Currency effects 0  
Balance, September 30, 2018 4,806  
Accumulated goodwill impairment 0 0
Operating Segments | Canada    
Goodwill [Roll Forward]    
Balance, December 31, 2017 3,494  
Goodwill acquired during the year 0  
Currency effects (96)  
Balance, September 30, 2018 3,398  
Accumulated goodwill impairment (1,016) (1,016)
Operating Segments | Non-solar DG    
Goodwill [Roll Forward]    
Balance, December 31, 2017 0  
Goodwill acquired during the year 0  
Currency effects 0  
Balance, September 30, 2018 0  
Accumulated goodwill impairment 0 0
Operating Segments | Other    
Goodwill [Roll Forward]    
Balance, December 31, 2017 24,507  
Goodwill acquired during the year 0  
Currency effects (228)  
Balance, September 30, 2018 24,279  
Accumulated goodwill impairment $ 0 $ 0