Entity probability percentage of property being sold.

No definition available.

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

- Definition

Number of vessels marketed to be sold.

+ References

No definition available.

+ Details

Name:	insw_NumberOfVesselsMarketedToBeSold
Namespace Prefix:	insw_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of vessels with impairment triggering events.

+ References

No definition available.

+ Details

Name:	insw_NumberOfVesselsWithImpairmentTriggeringEvents
Namespace Prefix:	insw_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Proceeds from costs of sale of property plant and equipment.

+ References

No definition available.

+ Details

Name:	insw_ProceedsFromCostsSaleOfPropertyPlantAndEquipment
Namespace Prefix:	insw_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of gain (loss) on sale or disposal of assets, including but not limited to property plant and equipment, intangible assets and equity in securities of subsidiaries or equity method investee.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3602-108585

+ Details

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

- Definition

The aggregate amount of write-downs for impairments recognized during the period for long lived assets held for use (including those held for disposal by means other than sale).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3602-108585

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109226691&loc=d3e2921-110230

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 958
-SubTopic 220
-Section 45
-Paragraph 11
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=114873921&loc=SL114875236-224282

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 45
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=109226348&loc=d3e2420-110228

+ Details

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

- Definition

Amount of the unrecorded obligation to transfer funds in the future for fixed or minimum amounts or quantities of goods or services at fixed or minimum prices (for example, as in take-or-pay contracts or throughput contracts).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 440
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=77896938&loc=d3e25336-109308

+ Details

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

- Details

Name:	us-gaap_PropertyPlantAndEquipmentByTypeAxis=insw_LongRangeOneVesselMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PropertyPlantAndEquipmentByTypeAxis=insw_Aframax2002SoldMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PropertyPlantAndEquipmentByTypeAxis=insw_TwoVeryLargeCrudeCarriersVesselsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PropertyPlantAndEquipmentByTypeAxis=insw_OneOfTwoVeryLargeCrudeCarrierVesselsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PropertyPlantAndEquipmentByTypeAxis=insw_OneVeryLargeCrudeCarrierVesselsWithUnrecoverableCarryingValueMember
Namespace Prefix:
Data Type:	na
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Period Type:

VESSELS (Narrative) (Details) $ in Thousands	1 Months Ended		6 Months Ended
VESSELS (Narrative) (Details) $ in Thousands	Mar. 31, 2020 USD ($)	Jan. 31, 2020 USD ($)	Jun. 30, 2020 USD ($) property	Jun. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)
Impairment of long-lived assets held-for-use			$ 5,469	$ 0
Proceeds from disposal of vessels and other property	$ 1,400		$ 13,578	$ 9,090
Number of vessels marketed to be sold \| property			2
LR1 Vessel [Member]
Purchase agreement, purchase amount					$ 18,800
Aframax 2002-built Sold [Member]
Net gain (loss) on disposal of vessel		$ 4,100
2 VLCCs to be sold [Member]
Number of vessels marketed to be sold \| property			2
Probability percentage of property being sold			25.00%
Number of vessels with impairment triggering events \| property			2
1 of 2 VLCCs to be sold [Member]
Impairment of long-lived assets held-for-use			$ 5,500
1 VLCC with Unrecoverable Carrying Value [Member]
Number of vessels marketed to be sold \| property			1