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Summary of Significant Accounting Policies - Vessels and Depreciation (Details)
12 Months Ended
Dec. 31, 2020
USD ($)
Property, Plant and Equipment [Line Items]  
Vessels Salvage Value Per Lightweight Ton $ 300
Vessels useful life 5 years
Vessels | Minimum  
Property, Plant and Equipment [Line Items]  
Vessels useful life 25 years
Vessels | Maximum  
Property, Plant and Equipment [Line Items]  
Vessels useful life 30 years
Current Fleet | Minimum  
Property, Plant and Equipment [Line Items]  
Vessels useful life 8 years
Current Fleet | Maximum  
Property, Plant and Equipment [Line Items]  
Vessels useful life 22 years