Restricted Cash (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012
Restricted Cash And Investments [Abstract]
Retention accounts and other compensating cash balances amounts that are not pledged	$ 3,735

Represents the amount of not pledged retention accounts and other compensating cash balances, which the Company should maintain with the accounts of each of the lending banks.

No definition available.

Name:	ship_RetentionAccountsAndOtherCompensatingCashBalancesAmountsThatAreNotPledged
Namespace Prefix:	ship_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant