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Property and Equipment (Details) (USD $)
In Thousands, unless otherwise specified
12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Property and Equipment      
Property and equipment, gross $ 216,953 $ 181,523  
Less: Accumulated depreciation and amortization (88,042) (64,345)  
Property and equipment, net 128,911 117,178  
Depreciation and amortization expense 24,821 19,176 15,955
Land
     
Property and Equipment      
Property and equipment, gross 3,990 3,990  
Buildings and improvements
     
Property and Equipment      
Property and equipment, gross 13,096 12,392  
Buildings and improvements | Minimum
     
Property and Equipment      
Estimated Useful Life 3 years    
Buildings and improvements | Maximum
     
Property and Equipment      
Estimated Useful Life 39 years    
Construction equipment
     
Property and Equipment      
Property and equipment, gross 195,085 161,712  
Construction equipment | Minimum
     
Property and Equipment      
Estimated Useful Life 2 years    
Construction equipment | Maximum
     
Property and Equipment      
Estimated Useful Life 12 years    
Office equipment
     
Property and Equipment      
Property and equipment, gross $ 4,782 $ 3,429  
Office equipment | Minimum
     
Property and Equipment      
Estimated Useful Life 3 years    
Office equipment | Maximum
     
Property and Equipment      
Estimated Useful Life 7 years