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Debt Instrument, Variable Rate Minimum

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Fixed charge coverage ratio.

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Line of credit facility additional increase In maximum borrowing capacity.

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Line of credit facility basis spread on variable rate.

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Line of credit facility limitation amount.

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Percentage Required of Total Current Revolving Loan Commitments

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Percentage points added to the reference rate to compute the variable rate on the debt instrument.

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The price per share of the conversion feature embedded in the debt instrument.

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Ratio applied to the conversion of debt instrument into equity with equity shares divided by debt principal amount.

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Price of the entity's common stock which would be required to be attained for the conversion feature embedded in the debt instrument to become effective.

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Threshold period of specified consecutive trading days within which common stock price to conversion price of convertible debt instrument must exceed threshold percentage for specified number of trading days to trigger conversion feature.

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Minimum percentage of common stock price to conversion price of convertible debt instruments to determine eligibility of conversion.

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Threshold number of specified trading days that common stock price to conversion price of convertible debt instruments must exceed threshold percentage within a specified consecutive trading period to trigger conversion feature.

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Face (par) amount of debt instrument at time of issuance.

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Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium.

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Contractual interest rate for funds borrowed, under the debt agreement.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Amount, before accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

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Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

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Including the current and noncurrent portions, aggregate carrying amount of all types of notes payable, as of the balance sheet date, with initial maturities beyond one year or beyond the normal operating cycle, if longer.

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Debt (Details Textual)			3 Months Ended
Debt (Details Textual)	May 01, 2020 USD ($)	Jun. 02, 2016 USD ($) d $ / shares	Mar. 31, 2020 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2019 USD ($)	Oct. 31, 2019 USD ($)	Jun. 30, 2016 USD ($)
Debt Instrument [Line Items]
Debt liability component			$ 83,528,000		$ 106,044,000
Convertible Notes \| 2036 Senior Convertible Notes Repurchases
Debt Instrument [Line Items]
Face amount		$ 152,000,000					$ 152,000,000
Interest rate		4.00%					4.00%
Percentage of convertible senior notes principal required for repurchase		100.00%
Initial conversion rate		92.8074
Initial conversion price (in dollars per share) \| $ / shares		$ 10.78
Convertible debt instrument, closing price minimum \| $ / shares		$ 14.01
Convertible debt instrument, threshold percentage of stock price trigger		130.00%
Convertible debt instrument, threshold trading days \| d		20
Convertible debt instrument, threshold consecutive trading days \| d		30
Net proceeds from debt issuance		$ 147,118,000	25,949,000	$ 0
Fees and offering expenses		$ 4,882,000
Effective interest rate		1.53%
REG Ralston term loan
Debt Instrument [Line Items]
Debt liability component			$ 15,296,000		15,980,000
REG Ralston term loan \| Prime Rate
Debt Instrument [Line Items]
Basis spread on variable rate			2.25%
REG Danville
Debt Instrument [Line Items]
Debt liability component			$ 0		6,468,000
REG Danville \| LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate			4.00%
REG Capital term loan
Debt Instrument [Line Items]
Interest rate			3.99%
Debt liability component			$ 6,864,000		$ 6,929,000
Wells Fargo Revolver
Debt Instrument [Line Items]
Line of credit facility limitation amount			$ 40,000,000
Debt instrument, variable rate minimum			0.00%
Percentage required of total current revolving loan commitments			5.00%
Amount required of total current revolving loan commitments			$ 10,000,000
Line of credit			200,000,000			$ 150,000,000
Line of Credit Facility Additional Increase in Maximum Borrowing Capacity			$ 50,000,000
Wells Fargo Revolver \| Subsequent Event
Debt Instrument [Line Items]
Amount required of total current revolving loan commitments	$ 15,000,000
Line of credit	$ 150,000,000
Wells Fargo Revolver \| Minimum
Debt Instrument [Line Items]
LIBOR rate margin			1.75%
Fixed charge coverate ratio			1.0
Wells Fargo Revolver \| Maximum
Debt Instrument [Line Items]
LIBOR rate margin			2.25%
Fixed charge coverate ratio			1.0
Wells Fargo Revolver \| Maximum \| Subsequent Event
Debt Instrument [Line Items]
Percentage required of total current revolving loan commitments	10.00%