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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Revenue (Details) |  | 12 Months Ended
--- | --- | ---
Apr. 12, 2021 $ / shares | Jan. 31, 2021 USD ($) item contract MT $ / shares | Jan. 31, 2020 USD ($) $ / shares | Jan. 31, 2019 $ / shares
Cash and Cash Equivalents |  |  |  |
Amount held by the Trust in a money market fund |  | $ 12,500,941 | $ 768,512 |
Revenue from Contract with Customer [Abstract] |  |  |  |
Accrued income receivable |  | $ 249,477 | 69,588 |
Number of customer contracts | contract |  | 1 |  |
Net contract asset |  | $ 177,251 |  |
Net contract liability |  |  | 2,511,720 |
Contract asset |  | 239,132 | 192,059 |
Contract liability |  | $ 61,881 | $ 2,703,779 |
Fixed Property, Including Intangibles |  |  |  |
Percentage of fee interest owned by Mesabi Land Trust in the lands subject to the Peters Lease |  | 20.00% |  |
Distributions declared per unit (in dollars per unit) | $ / shares |  | $ 1.67 | $ 3.36 | $ 2.79
Subsequent Event [Member] |  |  |  |
Fixed Property, Including Intangibles |  |  |  |
Distributions declared per unit (in dollars per unit) | $ / shares | $ 0.89 |  |  |
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) | MT |  | 4 |  |
Base overriding royalties, second tier portion percentage |  | 85.00% |  |
Base overriding royalties, second tier shipment ceiling (in million tons) | MT |  | 2 |  |
Base overriding royalties, third tier portion percentage |  | 25.00% |  |
Base overriding royalties, third tier shipment threshold (in million tons) | MT |  | 6 |  |
Base overriding royalties, number of volume thresholds for transaction price | item |  | 4 |  |
Base overriding royalties, volume threshold for transaction price | MT |  | 1 |  |

X
- Definition The net amount of contract liabilities less contract assets, when that result is a liability balance. + References No definition available. + Details
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- Definition The net amount of contract assets less contract liabilities, when that result is an asset balance. + References No definition available. + Details
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- 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
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- 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
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- 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
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- Definition The number of volume thresholds used to determine the transaction price. + References No definition available. + Details
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- 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
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- 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
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- Definition Amount, after allowance for credit loss, of right to consideration from customer for product sold and service rendered in normal course of business, classified as current. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=121593590&loc=d3e4428-111522 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -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=120391452&loc=d3e13212-122682 Reference 3: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section 45 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=121566466&loc=d3e6676-107765 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 45 -Paragraph 9 -URI http://asc.fasb.org/extlink&oid=121593590&loc=d3e4531-111522 + Details
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- Definition Amount, after allowance for credit loss, of right to consideration in exchange for good or service transferred to customer when right is conditioned on something other than passage of time, classified as current. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 606 -SubTopic 10 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=121556615&loc=SL49130531-203044 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 606 -SubTopic 10 -Section 45 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=121556615&loc=SL49130533-203044 Reference 3: 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=121604090&loc=SL49130549-203045 + Details
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