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

No definition available.

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Face amount of financial liability at time of sale and leaseback agreement.

No definition available.

Name:	ship_FinancialLiabilityFaceAmount
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Data Type:	xbrli:monetaryItemType
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Period Type:	instant

Liability for 15% of the difference between the market price and certain threshold prices, as set forth in the agreement, to the buyer-lessor of the sale and leaseback agreement.

No definition available.

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Amount of participation liability for 15% of the difference between the market price and certain threshold prices, as set forth in the agreement, to the buyer-lessor of the sale and leaseback agreement that will be applied against the vessel's hire in future years under the extended time charter agreement.

No definition available.

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Data Type:	xbrli:monetaryItemType
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- References

No definition available.

Name:	ship_SaleAndLeasebackTransactionAbstract
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Data Type:	xbrli:stringItemType
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Purchase price of vessel under a sale leaseback agreement.

No definition available.

Name:	ship_SaleLeasebackAgreementPurchasePriceOfVessel
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Data Type:	xbrli:monetaryItemType
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The implied average applicable interest rate under the transaction involving the sale of the property to another party and the lease of the property back to the seller.

No definition available.

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Amount of the required periodic payments applied to principal.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section S99
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-Topic 210
-Publisher FASB
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Difference between the fair value of payments made and the carrying amount of debt which is extinguished prior to maturity.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section 45
-Paragraph 28
-Subparagraph (b)
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-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482740/230-10-45-28

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
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Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
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Minimum amount of purchase arrangement in which the entity has agreed to expend funds to procure goods or services from a supplier.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 942
-SubTopic 235
-Name Accounting Standards Codification
-Section S99
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477314/942-235-S99-2

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 235
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-Name Accounting Standards Codification
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-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480738/235-10-S50-4

Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 235
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-Name Accounting Standards Codification
-Section S99
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-URI https://asc.fasb.org/1943274/2147480678/235-10-S99-3

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The cash outflow to repay long-term debt that is wholly or partially secured by collateral. Excludes repayments of tax exempt secured debt.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 230
-SubTopic 10
-Name Accounting Standards Codification
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Lease term for sale and leaseback transaction, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 842
-SubTopic 40
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
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Period Type:	duration

Name:	us-gaap_DebtInstrumentAxis=ship_FlagshipCargillSaleAndLeasebackMember
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