Name:	ship_DemurrageIncome
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Expense for bonus payments made to the charterer by the vessel owner when loading or discharging time is faster than the stipulated time in the voyage charter agreement.

No definition available.

Name:	ship_DespatchExpense
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- References

No definition available.

Name:	ship_VesselRevenueAndVoyageExpensesAbstract
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Port, canal and bunker expenses and commission costs that are incurred on time-charter and voyage-charter arrangements. Commissions are paid directly to brokers by the company.

No definition available.

Name:	ship_VoyageExpenses
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Amount, after allowance for credit loss, of right to consideration from customer for product sold and service rendered in normal course of business, classified as current.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 310
-SubTopic 10
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-Section 45
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-URI https://asc.fasb.org/1943274/2147481990/310-10-45-2

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For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 42
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-URI https://asc.fasb.org/1943274/2147482810/280-10-50-42

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 275
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-URI https://asc.fasb.org/1943274/2147482861/275-10-50-18

Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 275
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Reference 4: http://www.xbrl.org/2003/role/disclosureRef
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Reference 5: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 275
-SubTopic 10
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Reference 6: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 275
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 18
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482861/275-10-50-18

Reference 7: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 275
-SubTopic 10
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-Section 50
-Paragraph 18
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482861/275-10-50-18

Name:	us-gaap_ConcentrationRiskPercentage1
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Data Type:	dtr-types:percentItemType
Balance Type:	na
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Amount of deferred income excluding obligation to transfer product and service to customer for which consideration has been received or is receivable, classified as current.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name Accounting Standards Codification
-Section 25
-Paragraph 2
-SubTopic 10
-Topic 470
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481174/470-10-25-2

Name:	us-gaap_DeferredIncomeCurrent
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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Amount of deferred income excluding obligation to transfer product and service to customer for which consideration has been received or is receivable, classified as noncurrent.

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

- References

No definition available.

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

Amount of operating lease income from lease payments and variable lease payments paid and payable to lessor. Includes, but is not limited to, variable lease payments not included in measurement of lease receivable.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 842
-SubTopic 30
-Name Accounting Standards Codification
-Section 50
-Paragraph 5
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479773/842-30-50-5

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 270
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 6A
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482964/270-10-50-6A

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 842
-SubTopic 30
-Name Accounting Standards Codification
-Section 45
-Paragraph 3
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479016/842-30-45-3

Name:	us-gaap_OperatingLeaseLeaseIncome
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- References

No definition available.

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

Name:	srt_ProductOrServiceAxis=ship_SpotCharterMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	srt_ProductOrServiceAxis=ship_TimeCharterMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_ConcentrationRiskByBenchmarkAxis=us-gaap_SalesRevenueNetMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_ConcentrationRiskByTypeAxis=us-gaap_CustomerConcentrationRiskMember
Namespace Prefix:
Data Type:	na
Balance Type:
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Name:	srt_MajorCustomersAxis=ship_CustomersAccountingForMoreThan10PercentOfRevenuesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	srt_MajorCustomersAxis=ship_CustomerAMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	srt_MajorCustomersAxis=ship_CustomerBMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	srt_MajorCustomersAxis=ship_CustomerCMember
Namespace Prefix:
Data Type:	na
Balance Type:
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Name:	srt_MajorCustomersAxis=ship_CustomerDMember
Namespace Prefix:
Data Type:	na
Balance Type:
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