Name:	insw_DebtInstrumentCovenantFairMarketValueOfCoreCollateralVesselsThresholdPercentageOfOutstandingPrincipalAmount
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Debt instrument covenant limitation on total borrowings percentage of total assets.

No definition available.

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Represents the threshold amount for calculation of minimum liquidity level under the debt instrument covenant.

No definition available.

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Data Type:	xbrli:monetaryItemType
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Debt instrument covenant net worth.

No definition available.

Name:	insw_DebtInstrumentCovenantNetWorth
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Represents the threshold percentage of consolidated indebtedness

No definition available.

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Represents the adjustments to applicable core margin under credit agreement.

No definition available.

Name:	insw_DebtInstrumentThresholdLeverageRatio
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Data Type:	dtr-types:percentItemType
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States whether the entity was in compliance with the debt covenants throughout the reporting period, and describes facts and circumstances of any compliance failure.

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Face (par) amount of debt instrument at time of issuance.

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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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.

No definition available.

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Period Type:

Name:	us-gaap_LongtermDebtTypeAxis=us-gaap_SeniorNotesMember
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