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Goodwill and Intangible Assets - Summary of goodwill and intangible assets (Details) - USD ($)
$ in Thousands
Dec. 31, 2018
Dec. 31, 2017
Schedule Of Intangible Assets And Goodwill [Line Items]    
Goodwill gross carrying amount $ 56,588 $ 46,994
Goodwill accumulated amortization 0 0
Goodwill net carrying amount 56,588 46,994
Accumulated Amortization 7,031 5,183
Total 13,733  
Intangible Assets, Gross (Excluding Goodwill) 40,297 16,035
Intangible Assets, Net (Excluding Goodwill) 33,266 10,852
Trade names [Member]    
Schedule Of Intangible Assets And Goodwill [Line Items]    
Indefinite-lived Intangible Assets 19,533 9,074
Intangible Assets, Gross (Excluding Goodwill) 0 0
Intangible Assets, Net (Excluding Goodwill) 19,533 9,074
T&D [Member]    
Schedule Of Intangible Assets And Goodwill [Line Items]    
Goodwill gross carrying amount 40,224 40,224
Goodwill accumulated amortization 0 0
Goodwill net carrying amount 40,224 40,224
C&I [Member]    
Schedule Of Intangible Assets And Goodwill [Line Items]    
Goodwill gross carrying amount 16,364 6,770
Goodwill accumulated amortization 0 0
Goodwill net carrying amount 16,364 6,770
Backlog [Member]    
Schedule Of Intangible Assets And Goodwill [Line Items]    
Accumulated Amortization 1,889 989
Amortizable intangible assets gross carrying amount 2,789 989
Total 900 0
Customer relationships [Member]    
Schedule Of Intangible Assets And Goodwill [Line Items]    
Accumulated Amortization 4,970 4,069
Amortizable intangible assets gross carrying amount 17,280 5,277
Total 12,310 1,208
Trade names [Member]    
Schedule Of Intangible Assets And Goodwill [Line Items]    
Accumulated Amortization 172 125
Amortizable intangible assets gross carrying amount 695 695
Total $ 523 $ 570