v3.25.3

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Others (Details) - shares	3 Months Ended		9 Months Ended
	Oct. 31, 2025	Oct. 31, 2024	Oct. 31, 2025	Oct. 31, 2024
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES
Number of units outstanding	13,120,010	13,120,010	13,120,010	13,120,010
Percentage of fee interest owned by Mesabi Land Trust in the lands subject to the Peters Lease			20.00%

X

- Definition

Represents the percentage of fee interest held by Mesabi Land Trust in the lands subject to the Peters Lease.

+ References

No definition available.

+ Details

Name:	msb_PercentageOfFeeInterestHeldByLandTrustInLeaseProperty
Namespace Prefix:	msb_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

X

- References

No definition available.

+ Details

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

X

- Definition

Number of [basic] shares or units, after adjustment for contingently issuable shares or units and other shares or units not deemed outstanding, determined by relating the portion of time within a reporting period that common shares or units have been outstanding to the total time in that period.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 260
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482662/260-10-50-1

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 260
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 10
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482689/260-10-45-10

+ Details

Name:	us-gaap_WeightedAverageNumberOfSharesOutstandingBasic
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration