Significant Accounting Policies, Recent Accounting Pronouncements - Not Yet Adopted (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
JDH Notes [Member]
Recent Accounting Pronouncements - Not Yet Adopted [Abstract]
Unamortized BCF subject to change recorded in equity	$ 10,949	$ 18,360

Amount of a favorable spread to a debt holder between the amount of debt being converted and the value of the securities received upon conversion. This is an embedded conversion feature of convertible debt issued that is in-the-money at the commitment date.

No definition available.

Name:	ship_DebtInstrumentBeneficialConversionFeature
Namespace Prefix:	ship_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant