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Property and Equipment (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Property and equipment    
Gross property and equipment $ 732,720 $ 614,889
Less: accumulated depreciation and amortization (356,836) (303,112)
Property and equipment, net $ 375,884 311,777
Minimum    
Property and equipment    
Useful Life 3 years  
Maximum    
Property and equipment    
Useful Life 30 years  
Land and buildings    
Property and equipment    
Gross property and equipment $ 101,170 82,755
Useful Life 30 years  
Leasehold improvements    
Property and equipment    
Gross property and equipment $ 13,438 12,601
Office equipment    
Property and equipment    
Gross property and equipment $ 9,669 8,888
Office equipment | Minimum    
Property and equipment    
Useful Life 3 years  
Office equipment | Maximum    
Property and equipment    
Useful Life 5 years  
Construction equipment    
Property and equipment    
Gross property and equipment $ 439,875 392,454
Construction equipment | Minimum    
Property and equipment    
Useful Life 3 years  
Construction equipment | Maximum    
Property and equipment    
Useful Life 7 years  
Transportation equipment    
Property and equipment    
Gross property and equipment $ 112,170 101,855
Transportation equipment | Minimum    
Property and equipment    
Useful Life 3 years  
Transportation equipment | Maximum    
Property and equipment    
Useful Life 18 years  
Solar equipment    
Property and equipment    
Gross property and equipment $ 21,304  
Useful Life 25 years  
Construction in progress    
Property and equipment    
Gross property and equipment $ 35,094 $ 16,336