Asset acquisition number of vessels acquired.

No definition available.

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

- Definition

Number of contracts entered during the period.

+ References

No definition available.

+ Details

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

- Definition

Number of vessels delivered during the period.

+ References

No definition available.

+ Details

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

- Definition

The cash outflow associated with the acquisition of vessels and vessels improvements.

+ References

No definition available.

+ Details

Name:	insw_PaymentToAcquireVesselsAndVesselsImprovements
Namespace Prefix:	insw_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Remaining cost of construction of vessels

+ References

No definition available.

+ Details

Name:	insw_RemainingCostOfConstructionOfVessels
Namespace Prefix:	insw_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 842
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 7A
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478964/842-20-50-7A

+ Details

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

- Definition

Amount of unrecorded obligation to transfer funds in future for fixed or minimum amount or quantity of product and service at fixed or minimum price. Includes, but is not limited to, lease not yet commenced and take-or-pay and throughput contracts.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 440
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 4
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482648/440-10-50-4

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 842
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478964/842-20-50-3

+ 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_Lr1VesselOrderedToBeBuiltMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PropertyPlantAndEquipmentByTypeAxis=insw_OneOfSixLr1VesselDeliveredThirdMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PropertyPlantAndEquipmentByTypeAxis=insw_OneOfSixLr1VesselDeliveredFourthMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PropertyPlantAndEquipmentByTypeAxis=insw_TwoOfSixLr1VesselDeliveredMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

VESSELS (Vessel Acquisitions and Construction Commitments - Narrative) (Details)	1 Months Ended						3 Months Ended	6 Months Ended
	Jul. 31, 2026 USD ($) property	May 31, 2026 USD ($) property	Apr. 30, 2026 property	Mar. 31, 2026 property	Mar. 31, 2024 USD ($) property	Aug. 31, 2023 USD ($) property	Sep. 30, 2026 property	Jun. 30, 2026 USD ($) property contract	Dec. 31, 2025 property	Jun. 30, 2025 USD ($)
Property, Plant and Equipment [Line Items]
Payments to acquire vessels \| $								$ 122,873,000		$ 100,878,000
LR1 Vessel Ordered to be Built [Member]
Property, Plant and Equipment [Line Items]
Number of vessels acquired	4	4			6	6
Purchase agreement, purchase amount \| $	$ 244,000,000	$ 244,000,000			$ 359,000,000	$ 359,000,000
Payments to acquire vessels \| $								$ 0
Number Of Contracts \| contract								2
One Of Six LR1 Vessel Delivered Third [Member]
Property, Plant and Equipment [Line Items]
Number of vessels delivered				1
One Of Six LR1 Vessel Delivered Fourth [Member]
Property, Plant and Equipment [Line Items]
Number of vessels acquired			1
Two of Six LR1 Vessel Delivered [Member]
Property, Plant and Equipment [Line Items]
Number of vessels acquired								2	2
Remaining cost of construction of vessels \| $								$ 73,000,000
Two of Six LR1 Vessel Delivered [Member] \| Scenario, Plan [Member]
Property, Plant and Equipment [Line Items]
Number of vessels acquired							2