Debt instrument covenant minimum security coverage percentage of aggregate loan principal.

No definition available.

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Namespace Prefix:	insw_
Data Type:	num:percentItemType
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- Definition

Debt instrument covenant percentage of total indebtedness.

+ References

No definition available.

+ Details

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Namespace Prefix:	insw_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Debt instrument interest expense coverage ratio.

+ References

No definition available.

+ Details

Name:	insw_DebtInstrumentInterestExpenseCoverageRatio
Namespace Prefix:	insw_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	instant

- Definition

Debt instrument maximum consolidated leverage ratio.

+ References

No definition available.

+ Details

Name:	insw_DebtInstrumentMaximumConsolidatedLeverageRatio
Namespace Prefix:	insw_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Debt instrument minimum consolidated liquidity total consolidated cash and cash equivalents.

+ References

No definition available.

+ Details

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Namespace Prefix:	insw_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Debt instrument minimum consolidated liquidity unrestricted consolidated cash and cash equivalents.

+ References

No definition available.

+ Details

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Namespace Prefix:	insw_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Debt instrument per piece of property covenant.

+ References

No definition available.

+ Details

Name:	insw_DebtInstrumentPerPieceOfPropertyCovenant
Namespace Prefix:	insw_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Debt instrument property aggregate covenant.

+ References

No definition available.

+ Details

Name:	insw_DebtInstrumentPropertyAggregateCovenant
Namespace Prefix:	insw_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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

- Definition

Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ 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)(3)
-URI http://asc.fasb.org/extlink&oid=109500613&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(a)(16))
-URI http://asc.fasb.org/extlink&oid=119400593&loc=d3e572229-122910

Reference 3: 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=6876686&loc=d3e534808-122878

Reference 4: 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=6877327&loc=d3e13212-122682

+ Details

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

- Details

Name:	srt_StatementScenarioAxis=us-gaap_ScenarioPlanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=insw_SeawaysHoldingCompanyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

DEBT (Sinosure Credit Facility) (Narrative) (Details) $ in Thousands	Jul. 31, 2020	Jun. 30, 2020	Mar. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Scenario, Plan [Member]
Debt Instrument [Line Items]
Debt instrument interest expense coverage ratio	2.50	2.25
Seaways Holding Company [Member]
Debt Instrument [Line Items]
Debt instrument interest expense coverage ratio			2.00
Sinosure Credit Facility [Member]
Debt Instrument [Line Items]
Long-term debt			$ 261,645	$ 267,443
Debt instrument covenant minimum security coverage percentage of aggregate loan principal			135.00%
Debt instrument maximum consolidated leverage ratio			0.60%
Debt instrument minimum consolidated liquidity unrestricted consolidated cash and cash equivalents			$ 25,000
Debt instrument minimum consolidated liquidity total consolidated cash and cash equivalents			$ 50,000
Debt instrument covenant percentage of total indebtedness			5.00%
Debt instrument property aggregate covenant			$ 9,000
Debt instrument per piece of property covenant			$ 1,500