Annual report pursuant to Section 13 and 15(d)

Commitments and Contingencies - Future Commitments to Pay for Usage of Port Facilities (Details 2)

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Commitments and Contingencies - Future Commitments to Pay for Usage of Port Facilities (Details 2) - Port Facility Commitments
$ in Thousands
Dec. 31, 2017
USD ($)
Other Commitments [Line Items]  
2018 $ 30,509
2019 21,460
2020 21,928
2021 18,179
2022 5,137
Thereafter 41,095
Total minimum annual payments $ 138,308