Statement of Financial Position [Abstract] Short-term investments Total current assets Operating lease right-of-use assets Total assets Assets Current operating lease liabilities Total current liabilities Long-term operating lease liabilities Total long-term liabilities Total REX shareholders’ equity Total equity Balance Balance Total liabilities and equity Income Statement [Abstract] Gross profit Segment gross profit (loss): Income before income taxes Income (loss) before income taxes: Net income Net income Net income including noncontrolling interests Net income attributable to REX common shareholders Net income 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) 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] Amortization of operating lease right-of-use assets Dividends received from equity method investee Proceeds from Equity Method Investment, Distribution Net cash provided by operating activities Sale of short-term investments Net cash provided by (used in) investing activities Net cash used in financing activities Net increase (decrease) in cash, cash equivalents and restricted cash Cash, cash equivalents and restricted cash, beginning of period Cash, cash equivalents and restricted cash, end of period Non cash financing activities – Stock awards issued Initial right-of-use assets and liabilities recorded upon adoption of ASC 842 Right-of-use assets acquired and liabilities incurred upon lease execution Condensed Financial Information Disclosure [Abstract] Accounting Policies [Abstract] Schedule of Components of Inventory [Abstract] Ethanol and other finished goods Work in process Grain and other raw materials Total Inventory Revenue from Contract with Customer [Abstract] 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 lease liabilities Property, Plant and Equipment, Type [Axis] 3743 Railroad Equipment [Member] Schedule of Operating Lease Agreements for Rail Cars and Other Equipment [Abstract] Fair Value Disclosures [Abstract] Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis [Abstract] Asset Class [Axis] Derivative Financial Instruments, Assets [Member] Investment in cooperative Forward purchase contract asset Total assets Liability Class [Axis] Derivative Financial Instruments, Liabilities [Member] Forward purchase contract 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] Property, Plant and Equipment [Abstract] Schedule of Property and Equipment [Abstract] Total Property and equipment, net Disclosure Text Block Supplement [Abstract] Schedule of Other Assets [Abstract] Deferred income taxes Total Other assets Schedule of accrued expenses and other current liabilities [Abstract] Accrued transportation related items Total 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] Investments Schedule [Abstract] Schedule of Equity Method Investments [Abstract] Schedule of Financial information For Equity Method Investment [Abstract] Investment, Name [Axis] Big River [Member] Schedule of Held To Maturity Securities [Abstract] 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] Unrecognized tax benefits, beginning of period Unrecognized tax benefits, end of period Commitments and Contingencies Disclosure [Abstract] Related Party Transactions [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] 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 Ex Transition Period Entity Filer Category Entity Interactive Data Current Entity Registrant Name Entity Shell Company Entity Small Business Assets: Current assets: Cash and cash equivalents Restricted cash Accounts receivable Refundable income taxes Prepaid expenses and other Equity method investment Big River Liabilities and equity: Current liabilities: Accounts payable, trade Accrued expenses and other current liabilities Long-term liabilities: Deferred taxes Other long-term liabilities Equity: REX shareholders’ equity: Common stock Paid-in capital Retained earnings Noncontrolling interests Net sales and revenue Cost of sales Equity in income of unconsolidated affiliates Income from equity method investments Interest and other income, (net) Capital contributions Capital contributions from minority investor Stock based compensation expense Stock based compensation expense (in Shares) Treasury stock acquired Treasury stock acquired (in Shares) Cash flows from operating activities: Adjustments to reconcile net income to net cash provided by operating activities: Depreciation Deferred income tax Stock based compensation expense Changes in assets and liabilities: Accounts payable, trade Other liabilities Cash flows from investing activities: Cash flows from financing activities: Payments to noncontrolling interests holders Non cash investing activities – Accrued capital expenditures Non cash financing activities – Stock awards accrued Reconciliation of total cash, cash equivalents and restricted cash: Treasury stock Selling, general and administrative expenses Benefit for income taxes Benefit (provision) for income taxes: Net income attributable to noncontrolling interests Noncontrolling interests distribution and other Interest income from investments Loss on disposal of property and equipment Accounts receivable Inventories Other assets Capital expenditures Purchase of short-term investments Other Treasury stock acquired