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v3.22.1

NATURE OF BUSINESS AND ORGANIZATION (Details) | 12 Months Ended |
--- | --- | ---
Jan. 31, 2022 item shares | Jan. 31, 2021 shares
NATURE OF BUSINESS AND ORGANIZATION |  |
Period of termination of the Trust after the death of the survivor of persons named in the exhibit | 21 years |
Number of persons named in the exhibit to the Agreement of Trust | item | 25 |
Age of the youngest survivor | 54 years |
Beneficial interest in the Trust (in units) | shares | 13,120,010 | 13,120,010

X
- Definition Represents the number of persons named in the exhibit to the Agreement of Trust. + References No definition available. + Details
Name: | msb_NumberOfPersonsNamedInExhibitToAgreementOfTrust
Namespace Prefix: | msb_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

X
- Definition Represents the termination period of the Trust after the death of the last survivor of the persons named in the exhibit as per the Agreement of Trust. + References No definition available. + Details
Name: | msb_PeriodOfTerminationAfterDeathOfLastSurvivor
Namespace Prefix: | msb_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Represents the believed age of the youngest surviving member named in the exhibit to the Agreement of Trust. + References No definition available. + Details
Name: | msb_TrustAgreementAgeOfYoungestSurvivor
Namespace Prefix: | msb_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- References No definition available. + Details
Name: | us-gaap_OrganizationConsolidationAndPresentationOfFinancialStatementsAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Number of shares issued which are neither cancelled nor held in the treasury. + References No definition available. + Details
Name: | us-gaap_SharesOutstanding
Namespace Prefix: | us-gaap_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | instant