XML 34 R20.htm IDEA: XBRL DOCUMENT
v3.19.1

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details) | 12 Months Ended |
--- | --- | ---
Jan. 31, 2019 USD ($) item MT | Jan. 31, 2018 USD ($)
Cash and Cash Equivalents |  |
Amount held by the Trust in a money market fund | $ | $ 209,709 | $ 314,835
Revenue from Contract with Customer [Abstract] |  |
Accrued income receivable | $ | $ 2,339,060 | $ 1,956,091
Fixed Property, Including Intangibles |  |
Percentage of fee interest owned by Mesabi Land Trust in the lands subject to the Peters Lease | 20.00% |
Base Overriding Royalties |  |
Revenue from Contract with Customer [Abstract] |  |
Base overriding royalties, first tier portion percentage | 90.00% |
Base overriding royalties, first tier shipment ceiling (in million tons) | 4 |
Base overriding royalties, second tier portion percentage | 85.00% |
Base overriding royalties, second tier shipment ceiling (in million tons) | 2 |
Base overriding royalties, third tier portion percentage | 25.00% |
Base overriding royalties, third tier shipment threshold (in million tons) | 6 |
Base overriding royalties, number of volume thresholds for transaction price | item | 4 |
Base overriding royalties, volume threshold for transaction price | 1 |

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

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: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition The ceiling quantity for the first tier of base overriding royalties earned. Shipments up to this amount are subject to the first tier portion percentage in calculating the royalties earned. + References No definition available. + Details
Name: | msb_RevenueCeilingQuantityForFirstTierOfConsideration
Namespace Prefix: | msb_
Data Type: | num:massItemType
Balance Type: | na
Period Type: | duration

X
- Definition The ceiling quantity for the second tier of base overriding royalties earned. Shipments up to this amount, above the first tier ceiling, are subject to the second tier portion percentage in calculating the royalties earned. + References No definition available. + Details
Name: | msb_RevenueCeilingQuantityForSecondTierOfConsideration
Namespace Prefix: | msb_
Data Type: | num:massItemType
Balance Type: | na
Period Type: | duration

X
- Definition The number of volume thresholds used to determine the transaction price. + References No definition available. + Details
Name: | msb_RevenueNumberOfVolumeThresholdsForVariableTransactionPrice
Namespace Prefix: | msb_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

X
- Definition The percentage applied to the quantity shipped in the first tier, to determine the quantity on which royalties are earned. + References No definition available. + Details
Name: | msb_RevenuePortionPercentageForFirstTierOfConsideration
Namespace Prefix: | msb_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition The percentage applied to the quantity shipped in the second tier, to determine the quantity on which royalties are earned. + References No definition available. + Details
Name: | msb_RevenuePortionPercentageForSecondTierOfConsideration
Namespace Prefix: | msb_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition The percentage applied to the quantity shipped in the third tier, to determine the quantity on which royalties are earned. + References No definition available. + Details
Name: | msb_RevenuePortionPercentageForThirdTierOfConsideration
Namespace Prefix: | msb_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition The threshold quantity for the third tier of base overriding royalties earned. Shipments above this amount are subject to the third tier portion percentage in calculating the royalties earned. + References No definition available. + Details
Name: | msb_RevenueThresholdQuantityForThirdTierOfConsideration
Namespace Prefix: | msb_
Data Type: | num:massItemType
Balance Type: | na
Period Type: | duration

X
- Definition The quantity shipped which serves as a threshold to determine transaction price. + References No definition available. + Details
Name: | msb_RevenueVolumeThresholdForTransactionPrice
Namespace Prefix: | msb_
Data Type: | num:massItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount due from customers or clients, within one year of the balance sheet date (or the normal operating cycle, whichever is longer), for goods or services (including trade receivables) that have been delivered or sold in the normal course of business, reduced to the estimated net realizable fair value by an allowance established by the entity of the amount it deems uncertain of collection. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 606 -SubTopic 10 -Section 50 -Paragraph 8 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=109196051&loc=SL49130549-203045 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(3)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
Name: | us-gaap_AccountsReceivableNetCurrent
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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

X
- Definition Investment in short-term money-market instruments (such as commercial paper, banker's acceptances, repurchase agreements, government securities, certificates of deposit, and so forth) which are highly liquid (that is, readily convertible to known amounts of cash) and so near their maturity that they present an insignificant risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify as cash equivalents by definition. Original maturity means an original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three-years ago does not become a cash equivalent when its remaining maturity is three months. + References No definition available. + Details
Name: | us-gaap_MoneyMarketFundsAtCarryingValue
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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

X
- Details
Name: | us-gaap_ContractWithCustomerBasisOfPricingAxis=msb_RoyaltiesBasedOnProductShippedBaseAmountMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |