Subsequent Events	12 Months Ended
Subsequent Events	Dec. 31, 2021
Subsequent Events [Abstract]
Subsequent Events	SUBSEQUENT EVENTS Proposed Merger On February 27, 2022, the Company entered into an Agreement and Plan of Merger (the “Merger Agreement”) with Chevron Corporation (''Parent'') and Cyclone Merger Sub Inc., a wholly owned subsidiary of Parent (“Merger Subsidiary” and together with Parent, “Buyer”). Pursuant to the terms and conditions set forth in the Merger Agreement, Merger Subsidiary will merge with and into REG (the ''Merger'') with REG continuing as the surviving corporation of the Merger and as a wholly owned subsidiary of Parent. At the Effective Time, each share of common stock that is issued and outstanding immediately prior to the Effective Time (other than shares to be cancelled pursuant to the Merger Agreement or shares of common stock held by holders who have made a valid demand for appraisal in accordance with Section 262 of the Delaware General Corporation Law), will be automatically converted into the right to receive the Merger Consideration. At the Effective Time, and as a result of the Merger: •Each Company SAR will vest and be cancelled and converted into the right to receive a cash payment, less any applicable withholding taxes, equal to the product of (x) the excess, if any, of the Merger Consideration over the exercise price applicable to such Company SAR multiplied by (y) the number of shares of common stock subject to such Company SAR. •Each Company Director RSU will vest and be cancelled and converted into the right to receive a cash payment, less any applicable withholding taxes, equal to the product of (x) the Merger Consideration multiplied by (y) the number of shares of common stock subject to such Company Director RSU. •Each Company Employee RSU to the extent vested immediately prior to the Effective Time will be cancelled and converted into the right to receive a cash payment, less any applicable withholding taxes, equal to the product of (x) the Merger Consideration multiplied by (y) the number of vested shares of common stock subject to such Company Employee RSU. •Each Unvested Company Employee RSU Award and the Scheduled PSU Awards will be cancelled and converted into the right to receive an amount in cash, less any applicable withholding taxes, equal to the product of (x) the Merger Consideration multiplied by (y) the number of shares of common stock subject to such Assumed RSU Award. Each Assumed RSU Award will be subject to the vesting schedule applicable to the corresponding Unvested Company Employee RSU Award immediately prior to the Effective Time (including, with respect to the Scheduled PSU Awards, the performance vesting conditions). •Each Company PSU Award will be cancelled and converted into the right to receive an amount in cash, without interest and less any applicable withholding taxes, equal to the product of (A) the Merger Consideration multiplied by (B) the number of shares of common stock subject to such Company PSU Award (assuming that any performance based vesting conditions applicable to such Company PSU Award for any performance period that has not been completed as of the Effective Time are achieved at (x) with respect to Company PSU Awards granted in 2020 and 2021, the greater of the target performance levels and the levels based on actual achievement of pro-rated performance goals through the Effective Time or (y) with respect to Assumed PSU Awards, the target performance levels. Each Assumed PSU Award will be subject to the vesting schedule applicable to the corresponding Company PSU Award immediately prior to the Effective Time (other than any performance based vesting conditions). The closing of the Merger is subject to various conditions, including (i) the adoption of the Merger Agreement by holders of a majority of the issued and outstanding shares of our common stock; (ii) the expiration or termination of any applicable waiting period under the HSR Act and EU Clearance; (iii) the absence of any order or law prohibiting the consummation of the Merger, except if such order or law is immaterial to Parent and (iv) the accuracy of the representations and warranties contained in the Merger Agreement, subject to customary materiality qualifications, as of the date of the Merger Agreement and the closing of the Merger, and compliance in all material respects with the covenants and agreements contained in the Merger Agreement. In addition, the obligation of Parent and Merger Subsidiary to consummate the Merger is subject to the absence, since the date of the Merger Agreement, of a Company Material Adverse Effect. The closing of the Merger is not subject to a financing condition. Under the terms of the Merger Agreement, consummation of the Merger will occur on the second business day following the fulfillment or waiver of the conditions to closing of the Merger or at such other time as REG and Parent agree. The Company expects to incur certain significant costs relating to the Merger, such as legal, accounting, financial advisory, printing and other professional services fees, as well as other customary payments. In the event that the Merger is terminated, the Company may also be required to pay a cash termination fee to Parent of $91,000, as required under the Merger Agreement under certain circumstances.