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Transactions with related parties - Optional Vessel acquisitions from Sponsor/ Omnibus Agreement (Details) $ in Thousands | 1 Months Ended | 3 Months Ended | 12 Months Ended |  |
--- | --- | --- | --- | --- | ---
Feb. 06, 2018 | Mar. 30, 2017 | Apr. 12, 2016 | Dec. 31, 2017 USD ($) | Dec. 21, 2015 USD ($) | Dec. 31, 2016 USD ($) | Dec. 31, 2015 USD ($)
Related Party Transaction [Line Items] |  |  |  |  |  |  |
Debt instrument, remaining borrowing capacity |  |  |  | $ 0 |  | $ 0 |
Amended Omnibus Agreement | Legal right to acquire Sponsor's interests in Additional Optional Vessels |  |  |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |  |  |
Percentage of ownership in entity |  |  | 49.00% |  |  |  |
LNG Carrier Capacity |  |  | 172,000 |  |  |  |
Number Of Vessels |  |  | 5 |  |  |  |
Vessel Type |  |  | ARC7 LNG carrier |  |  |  |
$200 Million Term Loan Facility |  |  |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |  |  |
Debt instrument, remaining borrowing capacity |  |  |  |  |  |  | $ 66,700
Dynagas Holding Ltd | Legal right to acquire Sponsor's interests in Initial Optional Vessels |  |  |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |  |  |
Number Of Vessels |  |  |  | 4 |  |  |
Lena River |  |  |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |  |  |
Percentage of ownership in entity |  |  |  |  | 100.00% |  |
LNG Carrier Capacity |  |  |  | 155,000 |  |  |
Delivery Date |  |  |  | December 2015 |  |  |
Consideration for vessel and related time charter |  |  |  |  | $ 240,000 |  |
Lena River | Dynagas Holding Ltd |  |  |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |  |  |
Principal amount due |  |  |  |  | $ 35,000 |  |
Additional Optional Vessels |  |  |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |  |  |
Delivery Date |  |  |  | late 2017 and early 2018 |  |  |
Number Of Vessels |  |  |  | 2 |  |  |
Clean Ocean and Clean Planet | Extension of the purchase option exercise deadline |  |  |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |  |  |
Number Of Vessels |  | 2 |  |  |  |  |
Purchase option period, Expiration date |  | Mar. 31, 2018 |  |  |  |  |
Clean Horizon and Clean Vision | Subsequent Event | Extension of the purchase option exercise deadline |  |  |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |  |  |
Purchase option period, Expiration date | Dec. 31, 2018 |  |  |  |  |  |

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