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Basis of Presentation and General Information, Disposal of Vessels - 20F (Details) $ in Thousands | 12 Months Ended |
--- | --- | ---
Dec. 31, 2014 USD ($) Vessel | Mar. 11, 2014 USD ($) Vessel
Basis of Presentation and General Information [Abstract] |  |
Number of remaining vessels for sale | Vessel |  | 4
Outstanding debt and accrued interest | $ |  | $ 145,597
Number of vessels sold | Vessel | 4 |
Gain from sale of vessels | $ | $ 85,563 |

X
- Definition Amount of gain from sale of vessels during the period. + References No definition available. + Details
Name: | ship_GainOnSaleFromVessels
Namespace Prefix: | ship_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Number of remaining vessels for sale. + References No definition available. + Details
Name: | ship_NumberOfRemainingVessels
Namespace Prefix: | ship_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition Represents the number of vessels sold during the period. + References No definition available. + Details
Name: | ship_NumberOfVesselsSold
Namespace Prefix: | ship_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

X
- Definition Refers to amount of outstanding debt and accrued interest discharged during the period. + References No definition available. + Details
Name: | ship_OutstandingDebtAndAccruedInterest
Namespace Prefix: | ship_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- References No definition available. + Details
Name: | us-gaap_OrganizationConsolidationAndPresentationOfFinancialStatementsAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration