The corporate leverage ratio (expressed as a percentage) as defined in the loan facility.

No definition available.

Name:	ship_CorporateLeverageRatio
Namespace Prefix:	ship_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Face amount of the debt instrument that is available for borrowing at time the agreement is executed and/or amended.

+ References

No definition available.

+ Details

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

- Definition

The carrying amount of minimum liquidity requirement to be maintained in an earnings account by the borrower under the loan agreement.

+ References

No definition available.

+ Details

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

- Definition

The number of consecutive, periodic payment installments in which the debt is to be repaid.

+ References

No definition available.

+ Details

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

- Definition

The number of tranches the advance is available to be drawn down under the loan.

+ References

No definition available.

+ Details

Name:	ship_DebtInstrumentNumberOfTranches
Namespace Prefix:	ship_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

The threshold ratio (expressed as a percentage) of the market value of vessels plus additional security to the aggregate outstanding loan.

+ References

No definition available.

+ Details

Name:	ship_MarketValueOfVesselsPlusAdditionalSecurityAsPercentageOfAggregateOutstandingLoan
Namespace Prefix:	ship_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (b)(1)
-URI http://asc.fasb.org/extlink&oid=123466204&loc=SL6031897-161870

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(16))
-URI http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(16))
-URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878

+ Details

Name:	us-gaap_DebtInstrumentCarryingAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Description of the frequency of periodic payments (monthly, quarterly, annual).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22)
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 470
-Section 50
-Paragraph 3
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=123599511&loc=d3e64711-112823

+ Details

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

- Definition

Amount of the required periodic payments applied to principal.

+ References

+ Details

Name:	us-gaap_DebtInstrumentPeriodicPaymentPrincipal
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of payment greater than the preceding installment payments to be paid at final maturity date of debt.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentPeriodicPaymentTermsBalloonPaymentToBePaid
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The cash inflow from amounts received from issuance of long-term debt that is wholly or partially secured by collateral. Excludes proceeds from tax exempt secured debt.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 14
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=123570139&loc=d3e3255-108585

+ Details

Name:	us-gaap_ProceedsFromIssuanceOfSecuredDebt
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- References

No definition available.

+ Details

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

- Details

Name:	us-gaap_DebtInstrumentAxis=ship_LoanAgreementDatedApril222021Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableRateAxis=us-gaap_LondonInterbankOfferedRateLIBORMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=ship_LoanAgreementDatedApril222021TrancheAMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=ship_LoanAgreementDatedApril222021TrancheBMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Long-Term Debt and Other Financial Liabilities, ABB Loan Facility (Details) $ in Thousands				12 Months Ended
	Jun. 14, 2021 USD ($)	Apr. 26, 2021 USD ($)	Apr. 22, 2021 USD ($) Tranche	Dec. 31, 2021 USD ($) Installment	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Senior Long-Term Debt [Abstract]
Proceeds from drawdown				$ 180,320	$ 22,500	$ 6,422
Balance outstanding				$ 218,551	$ 173,289
ABB Loan Facility [Member]
Senior Long-Term Debt [Abstract]
Borrowing capacity			$ 15,500
Number of tranches \| Tranche			2
Market value of vessels plus additional security as percentage of aggregate outstanding loan				1.30
Minimum liquidity to be maintained in earnings account				$ 300
Balance outstanding				$ 14,700
ABB Loan Facility [Member] \| Maximum [Member]
Senior Long-Term Debt [Abstract]
Corporate leverage ratio				85.00%
ABB Loan Facility [Member] \| LIBOR [Member]
Senior Long-Term Debt [Abstract]
Margin on variable rate			4.00%
Tranche A [Member]
Senior Long-Term Debt [Abstract]
Proceeds from drawdown		$ 7,500
Number of consecutive payment installments \| Installment				18
Frequency of periodic payment				quarterly
Installment payment				$ 200
Balloon payment				$ 3,900
Tranche B [Member]
Senior Long-Term Debt [Abstract]
Proceeds from drawdown	$ 8,000
Number of consecutive payment installments \| Installment				18
Frequency of periodic payment				quarterly
Installment payment				$ 200
Balloon payment				$ 4,400