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Intangible Assets Narrative (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 1997
Nov. 16, 2017
Finite-Lived Intangible Assets [Line Items]          
Intangible assets $ 14,413 $ 23,989      
Net intangible assets 6,320 16,341      
Amortization of Intangible Assets 616 530 $ 453    
Future Amortization of Intangible Assets          
2018 616        
2019 616        
2020 616        
2021 616        
2022 616        
Concession Fees [Member]          
Finite-Lived Intangible Assets [Line Items]          
Intangible assets 6,800 6,800      
Accumulated amortization of intangible assets 5,508 5,236      
Other Intangible Assets [Member]          
Finite-Lived Intangible Assets [Line Items]          
Intangible assets 7,613 17,189      
Accumulated amortization of intangible assets 2,585 $ 2,412      
Service Agreements [Member]          
Finite-Lived Intangible Assets [Line Items]          
Intangible assets 3,771        
Useful life of intangible assets       25 years  
Infrastructure [Member]          
Finite-Lived Intangible Assets [Line Items]          
Intangible assets 2,537        
Contractual Rights [Member]          
Finite-Lived Intangible Assets [Line Items]          
Intangible assets 1,040        
Other Miscellaneous Intangibles [Member]          
Finite-Lived Intangible Assets [Line Items]          
Intangible assets $ 265        
Water Rights [Member]          
Finite-Lived Intangible Assets [Line Items]          
Intangible assets         $ 10,781
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