LEASES (Future Minimum Revenues on Charters-Out) (Details) - Charters-Out [Member] $ in Thousands	9 Months Ended
Sep. 30, 2024 USD ($)
Operating Leases, Future Minimum Payments Receivable [Abstract]
2024	$ 36,528
2025	114,169
2026	79,611
2027	39,433
2028	34,038
Thereafter	41,013
Net minimum lease payments	$ 344,791
2024, revenue days	1332 days
2025, revenue days	4112 days
2026, revenue days	2699 days
2027, revenue days	1259 days
2028, revenue days	1098 days
Thereafter	1323 days
Revenue Days	11823 days

Number of revenue days.

No definition available.

Name:	insw_NumberOfRevenueDays
Namespace Prefix:	insw_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Operating leases revenue days after year five.

+ References

No definition available.

+ Details

Name:	insw_OperatingLeasesRevenueDaysAfterYearFive
Namespace Prefix:	insw_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Operating leases revenue days current.

+ References

No definition available.

+ Details

Name:	insw_OperatingLeasesRevenueDaysCurrent
Namespace Prefix:	insw_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Operating leases revenue days year five.

+ References

No definition available.

+ Details

Name:	insw_OperatingLeasesRevenueDaysYearFive
Namespace Prefix:	insw_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Operating leases revenue days year four.

+ References

No definition available.

+ Details

Name:	insw_OperatingLeasesRevenueDaysYearFour
Namespace Prefix:	insw_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Operating leases revenue days year three.

+ References

No definition available.

+ Details

Name:	insw_OperatingLeasesRevenueDaysYearThree
Namespace Prefix:	insw_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Operating leases revenue days year two.

+ References

No definition available.

+ Details

Name:	insw_OperatingLeasesRevenueDaysYearTwo
Namespace Prefix:	insw_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- References

No definition available.

+ Details

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

- Definition

Amount of lease payments to be received by lessor for operating lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 842
-SubTopic 30
-Name Accounting Standards Codification
-Section 50
-Paragraph 12
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479773/842-30-50-12

+ Details

Name:	us-gaap_LessorOperatingLeasePaymentsToBeReceived
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of lease payments to be received by lessor in period after fifth rolling twelve months following latest statement of financial position date for operating lease. For interim and annual periods when interim periods are reported on rolling approach, from latest statement of financial position date.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 842
-SubTopic 30
-Name Accounting Standards Codification
-Section 50
-Paragraph 12
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479773/842-30-50-12

+ Details

Name:	us-gaap_LessorOperatingLeasePaymentsToBeReceivedAfterRollingYearFive
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of lease payments to be received by lessor in next rolling twelve months following latest statement of financial position date for operating lease. For interim and annual periods when interim periods are reported on rolling approach, from latest statement of financial position date.

+ References

+ Details

Name:	us-gaap_LessorOperatingLeasePaymentsToBeReceivedNextRollingTwelveMonths
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of lease payments to be received by lessor in fifth rolling twelve months following latest statement of financial position date for operating lease. For interim and annual periods when interim periods are reported on rolling approach, from latest statement of financial position date.

+ References

+ Details

Name:	us-gaap_LessorOperatingLeasePaymentsToBeReceivedRollingYearFive
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of lease payments to be received by lessor in fourth rolling twelve months following latest statement of financial position date for operating lease. For interim and annual periods when interim periods are reported on rolling approach, from latest statement of financial position date.

+ References

+ Details

Name:	us-gaap_LessorOperatingLeasePaymentsToBeReceivedRollingYearFour
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of lease payments to be received by lessor in third rolling twelve months following latest statement of financial position date for operating lease. For interim and annual periods when interim periods are reported on rolling approach, from latest statement of financial position date.

+ References

+ Details

Name:	us-gaap_LessorOperatingLeasePaymentsToBeReceivedRollingYearThree
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of lease payments to be received by lessor in second rolling twelve months following latest statement of financial position date for operating lease. For interim and annual periods when interim periods are reported on rolling approach, from latest statement of financial position date.

+ References

+ Details

Name:	us-gaap_LessorOperatingLeasePaymentsToBeReceivedRollingYearTwo
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis=insw_ChartersOutMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: