Statement of Financial Position [Abstract] Short-term investments Short-term Investments Total current assets Current assets TOTAL ASSETS Assets Total assets Total current liabilities Current liabilities Total long term liabilities Long-term liabilities Total REX shareholders’ equity Total equity Balance Balance TOTAL LIABILITIES AND EQUITY Income Statement [Abstract] Gross profit Gross profit Segment gross profit (loss): Gross profit (loss) (Loss) income before income taxes (Loss) income before income taxes: Net income Net income Net income (loss) Statement of Stockholders' Equity [Abstract] Balance (in Shares) Balance (in Shares) Equity Components [Axis] Common Stock [Member] Treasury Stock [Member] Additional Paid-in Capital [Member] Retained Earnings [Member] Noncontrolling Interest [Member] Statement of Cash Flows [Abstract] Depreciation Dividends received from equity method investments Proceeds from Equity Method Investment, Distribution Interest income from investments Loss on sale of investment Income taxes refundable Accrued expenses and other liabilities Net cash provided by operating activities Sale of short-term investments Acquisition of business, net of cash acquired Proceeds from sale of investment Proceeds from sale of real estate and property and equipment Repayment of note receivable Net cash used in investing activities Payments to noncontrolling interests holders Net cash used in financing activities CASH, CASH EQUIVALENTS AND RESTRICTED CASH-Beginning of year CASH, CASH EQUIVALENTS AND RESTRICTED CASH-End of year Cash, cash equivalents and restricted cash, end of period Accounting Policies [Abstract] Schedule of Components of Basis of Presentation [Abstract] Total Schedule of Components of Inventory [Abstract] Total Inventory Schedule of Property Plant and Equipment [Abstract] Total Property and equipment - net Disclosure Text Block Supplement [Abstract] Schedule of Equity Method Investments [Abstract] Schedule of Condensed Balance Sheet [Abstract] Total liabilities Liabilities Legal Entity [Axis] Big River [Member] Schedule of Financial information For Equity Method Investment [Abstract] Net income Net income attributable to REX common shareholders Net income (loss) attributable to REX common shareholders Net Income (Loss) Attributable to Parent Investment, Name [Axis] Business Combinations [Abstract] Schedule of Estimated Fair Values of Assets Acquired at Acquisition Date [Abstract] Fair Value Disclosures [Abstract] Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis [Abstract] Total assets Forward purchase contracts liability Fair Value Hierarchy and NAV [Axis] Fair Value, Inputs, Level 1 [Member] Fair Value, Inputs, Level 2 [Member] Fair Value, Inputs, Level 3 [Member] Schedule of Other Assets [Abstract] Total Other assets Schedule of accrued expenses and other current liabilities [Abstract] Total Accrued expenses and other current liabilities (includes $0.5 million and $1.6 million with related parties at January 31, 2020 and 2019, respectively) Disclosure Text Block [Abstract] Schedule of Components of Lease Expense [Abstract] Total lease expense Schedule of Future Minimum Rental Payments for Operating Leases [Abstract] Total Operating Leases, Future Minimum Payments Due Property Subject to or Available for Operating Lease [Axis] 3743 Railroad Equipment [Member] Stockholders' Equity Note [Abstract] Schedule of Common Stock [Abstract] Derivative Instruments and Hedging Activities Disclosure [Abstract] Schedule of Fair Values for Derivative Financial Instruments [Abstract] Derivative Instrument [Axis] Commodity Contract [Member] Forward Contracts [Member] Schedule of Non-Vested Restricted Stock Award Activity [Abstract] Non-Vested Shares, Beginning of Period Non-Vested Shares, End of Period Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number Weighted Average Grant Date Fair Value, Beginning of Period (in Dollars) Weighted Average Grant Date Fair Value, End of Period (in Dollars) Income Tax Disclosure [Abstract] Schedule of Unrecognized Tax Benefits Roll Forward [Abstract] Schedule of Deferred Tax Assets and Liabilities [Abstract] Total Total Schedule of Effective Income Tax Reconciliation [Abstract] Federal income tax at statutory rate State and local taxes, net of federal tax benefit Section 45 production tax credits Research and experimentation credits Tax Cuts and Jobs Act Domestic production activities deduction Uncertain tax positions Noncontrolling interest Other Total Unrecognized tax benefits, beginning of year Unrecognized tax benefits, end of year Loss Contingency [Abstract] Segment Reporting [Abstract] Schedule Of Segment Results And Assets [Abstract] Segments [Axis] Ethanol [Member] Refined Coal [Member] Corporate and Other [Member] Dried Distillers Grains [Member] Non-Food Grade Corn Oil [Member] Modified Distillers Grains [Member] Other Segments [Member] Assets [Member] Schedule Of Segment Assets [Abstract] Quarterly Financial Information Disclosure [Abstract] Schedule of Quarterly Financial Information [Abstract] Related Party Transactions [Abstract] Subsequent Events [Abstract] SEC Schedule, 12-09, Valuation and Qualifying Accounts [Abstract] Balance Balance Valuation allowance Deferred Tax Assets, Valuation Allowance Amendment Flag Current Fiscal Year End Date Document Fiscal Period Focus Document Fiscal Year Focus Document Period End Date Document Type Entity Central Index Key Entity Common Stock, Shares Outstanding Entity Current Reporting Status Entity Emerging Growth Company Entity Filer Category Entity Interactive Data Current Entity Public Float Entity Registrant Name Entity Shell Company Entity Small Business Entity Voluntary Filers Entity Well-known Seasoned Issuer CURRENT ASSETS: Cash and cash equivalents Restricted cash Accounts receivable Refundable income taxes Prepaid expenses and other Operating lease right-of-use assets Equity method investments Carrying amount Equity Method Investments LIABILITIES AND EQUITY CURRENT LIABILITIES: Accounts payable – trade (includes $0.7 million and $1.9 million with related related parties at January 31, 2020 and 2019, respectively) Accounts payable, related parties (in Dollars) Accounts Payable, Related Parties, Current Current operating lease liabilities Accrued expenses, related parties (in Dollars) LONG TERM LIABILITIES: Deferred taxes Long-term operating lease liabilities Other long term liabilities EQUITY: REX shareholders’ equity: Common stock, 45,000 shares authorized, 29,853 shares issued at par Common stock, shares authorized Authorized shares Common stock, shares issued Issued shares Paid in capital Retained earnings Treasury stock, shares Noncontrolling interests Net sales and revenue Cost of sales (includes $171.5 million, $176.8 million and $154.5 million with related parties for the years ended January 31, 2020, 2019 and 2018, respectively) Cost of sales, related parties Selling, general, and administrative expenses, related parties Equity in income of unconsolidated affiliates Income from equity method investments Income (Loss) from Equity Method Investments Interest and other income, net Weighted average shares outstanding – basic and diluted (in Shares) Basic and diluted net income per share attributable to REX common shareholders (in Dollars per share) Basic and diluted net income (loss) per share attributable to REX common shareholders (in Dollars per share) Capital contributions