Transactions with Related Parties-Subsidiary Disposal (Details)	12 Months Ended
Dec. 31, 2012
Related Party Transactions [Abstract]
Percentage of ownership in BET disposed	100.00%

The percentage of ownership interest of the parent company in the subsidiary.

No definition available.

Name:	ship_PercentageOfOwnershipInterestInSubsidiary
Namespace Prefix:	ship_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration