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Intangible Assets Narrative (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 1997
Finite-Lived Intangible Assets [Line Items]        
Intangible assets $ 15,799 $ 14,413    
Net intangible assets 7,059 6,320    
Amortization of Intangible Assets 647 616 $ 530  
Future Amortization of Intangible Assets        
2018 647      
2019 647      
2020 647      
2021 647      
2022 647      
Concession Fees [Member]        
Finite-Lived Intangible Assets [Line Items]        
Intangible assets 6,800 6,800    
Accumulated amortization of intangible assets 5,780 5,508    
Other Intangible Assets [Member]        
Finite-Lived Intangible Assets [Line Items]        
Intangible assets 8,999 7,613    
Accumulated amortization of intangible assets 2,960 $ 2,585    
Service Agreements [Member]        
Finite-Lived Intangible Assets [Line Items]        
Intangible assets 4,128      
Useful life of intangible assets       25 years
Infrastructure [Member]        
Finite-Lived Intangible Assets [Line Items]        
Intangible assets 3,831      
Contractual Rights [Member]        
Finite-Lived Intangible Assets [Line Items]        
Intangible assets $ 1,040      
Minimum [Member]        
Finite-Lived Intangible Assets [Line Items]        
Useful life of intangible assets 5 years      
Maximum [Member]        
Finite-Lived Intangible Assets [Line Items]        
Useful life of intangible assets 70 years