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Leases (Operating Leases) (Details) - drilling_rig
Aug. 30, 2019
Dec. 31, 2018
Dec. 31, 2016
Dec. 31, 2014
Lessee, Lease, Description [Line Items]        
Number of drilling rigs   2    
Sale leaseback term 2 years      
CO2 Compressor        
Lessee, Lease, Description [Line Items]        
Operating lease, term     84 months 84 months
Drilling Rigs        
Lessee, Lease, Description [Line Items]        
Operating lease, term   15 months    
Low        
Lessee, Lease, Description [Line Items]        
Sale leaseback, renewal term 1 year      
High        
Lessee, Lease, Description [Line Items]        
Sale leaseback, renewal term 2 years