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Basis of Presentation and General Information, Vessels Acquisitions - 20F (Details)				12 Months Ended
	Aug. 06, 2015 Vessel	Mar. 19, 2015 t	Dec. 23, 2014 t	Dec. 31, 2015 Vessel
Vessel Acquisitions [Abstract]
Number of vessels acquired				8
Leadership [Member]
Vessel Acquisitions [Abstract]
Dead weight tonnage | t		171,199	171,199
Dry Bulk Vessel [Member]
Vessel Acquisitions [Abstract]
Number of vessels acquired	7

X

- Definition

Deadweight tonnage (DWT) is a measure of vessels capacity in weight, and does not include the weight of the vessel.

+ References

No definition available.

+ Details

Name:	ship_DeadWeightTonnage
Namespace Prefix:	ship_
Data Type:	num:massItemType
Balance Type:	na
Period Type:	duration

X

- Definition

The number of vessels acquired during the period.

+ References

No definition available.

+ Details

Name:	ship_NumberOfVesselsAcquired
Namespace Prefix:	ship_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

X

- References

No definition available.

+ Details

Name:	us-gaap_PropertyPlantAndEquipmentOwnedNetAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Details

Name:	us-gaap_BusinessAcquisitionAxis=ship_DWTVesselMVLeadershipMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_PropertyPlantAndEquipmentByTypeAxis=ship_DryBulkVesselMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: