Note 6 - Derivative Financial Instruments (Details Textual) xbrli-pure in Thousands	12 Months Ended
Mar. 31, 2021 USD ($) g T	Mar. 31, 2020 USD ($)
Derivative, Number of Instruments Held, Total		0
Derivative Instruments, Gain (Loss) Reclassification from Accumulated OCI to Income, Estimated Net Amount to be Transferred	$ 14,169,820
Derivative, Collateral, Right to Reclaim Cash	12,001,485
Accumulated Gain (Loss), Net, Cash Flow Hedge, Parent [Member]
Reclassification from AOCI, Current Period, Tax, Total	1,549,743
Closed Hedges with Hedged Transaction Still Expected to Occur [Member]
Derivative Instruments, Gain (Loss) Reclassification from Accumulated OCI to Income, Estimated Net Amount to be Transferred	6,839,740
Open Hedges Subject To Fair Value Changes [Member]
Derivative Instruments, Gain (Loss) Reclassification from Accumulated OCI to Income, Estimated Net Amount to be Transferred	7,330,080
Accounts Payable and Accrued Liabilities [Member] \| Commodity Contract [Member]
Hedging Liabilities, Current	$ 501,360
Other Current Assets [Member]
Derivative, Collateral, Right to Reclaim Cash		$ 12,001,485
Not Designated as Hedging Instrument [Member]
Derivative, Number of Instruments Held, Total	0
Not Designated as Hedging Instrument [Member] \| Short [Member]
Derivative, Nonmonetary Notional Amount, Mass (US Ton) \| T	1,860
Designated as Hedging Instrument [Member] \| Long [Member]
Derivative, Nonmonetary Notional Amount, Mass (US Ton) \| T	4,000
Designated as Hedging Instrument [Member] \| Short [Member]
Derivative, Nonmonetary Notional Amount, Mass (US Ton) \| g	43,740

Amount of right to receive cash collateral under master netting arrangements that have not been offset against derivative liabilities.

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The estimated value of gains (losses), net anticipated to be transferred in the future from accumulated other comprehensive income into earnings.

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- Definition

Nominal mass used to calculate payments on a derivative instrument.

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No definition available.

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The number of derivative instruments of a particular group held by the entity.

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Carrying amount as of the balance sheet date of the liability arising from a financial instrument or a contract used to mitigate a specified risk (hedge), and which are expected to be converted into cash or otherwise disposed of within a year or the normal operating cycle, if longer.

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- Definition

Amount of tax expense (benefit) of reclassification adjustment from accumulated other comprehensive income (loss).

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