Issuance of short-term commercial paper

On June 27, 2019, the Company entered into a framework agreement for participation in the issuance of commercial paper (the "Agreement") with Discount Capital Underwriting Ltd. under which the Company allowed the participants to submit proposals for purchasing and to purchase the Company's commercial paper ("Commercial Paper") in accordance with the provisions of the Agreement. On July 3, 2019, the Company completed the issuance of the Commercial Paper in the aggregate amount of $50.0 million. The Commercial Paper was issued for a period of 90 days and extends automatically for additional periods of 90 days each, for up to 5 years, unless the Company notifies the participants otherwise or a notice of termination is provided by the participants in accordance with the provisions of the Agreement. The Commercial Paper bears an annual interest of 3 months LIBOR +0.75% which is paid at the end of each 90 day periods.

Plumstriker Loan

On May 4, 2019, a wholly owned indirect subsidiary of the Company (“Plumstriker”) and its two subsidiaries entered into a $23.5 million loan agreement with a United States (“U.S.”) financing division of a leading global industrial company for the financing of two 20 MW battery energy storage projects located in New Jersey.

On May 30, 2019, Plumstriker completed the drawdown of the full loan amount, bearing interest of three months U.S. Libor plus a 3.5% margin. The loan will be repaid in 29 equal quarterly principal installments of 1.25% of the loan, and additional 14 unequal semi-annual principal payments, commencing June 30, 2019. The final maturity date of the loan is May 30, 2026. Proceeds of the loan were used to refinance investments in the said projects. The debt repayment of the loan is not guaranteed by the Company or any of its other subsidiaries.

Société Géneralé Loan

On April 9, 2019, an indirect subsidiary of the Company (“Guadeloupe”), entered into a $8.9 million loan agreement with Société Général. On April 29, 2019, Guadeloupe completed the drawdown of the full loan amount of the loan, bearing a fixed interest of 1.52%. The loan will be repaid in 28 quarterly principal installments, commencing July 29, 2019. The final maturity date of the loan is April 29, 2026. The loan has a limited guarantee by one of the Company’s subsidiaries.

Bpifrance Loan

On April 4, 2019, Guadeloupe, entered into a $8.9 million loan agreement with Banque Publique d’Investissement (“Bpifrance”). On April 29, 2019, Guadeloupe completed the drawdown of the full loan amount, bearing a fixed interest of 1.93%. The loan will be repaid in 20 equal quarterly principal installments, commencing June 30, 2021. The final maturity date of the loan is March 31, 2026. The loan is not guaranteed by the Company or any of its other subsidiaries.

Puna

On May 3, 2018, the Kilauea volcano located in close proximity to our Puna 38 MW geothermal power plant in the Puna district of Hawaii's Big Island erupted following a significant increase in seismic activity in the area. Before it stopped flowing, the lava covered the wellheads of three geothermal wells, monitoring wells and the substation of the Puna complex and an adjacent warehouse that stored a drilling rig that was also consumed by the lava. The insurance policy coverage for property and business interruption is provided by a consortium of insurers. All the insurers accepted and started paying for the costs to rebuild the destroyed substation, and during the first quarter of 2019, the Company received an additional $1.5 million of such proceeds. However, only some of the insurers accepted that the business interruption coverage started in May 2018 and during the first, second and third quarters of 2019, the Company received and recorded an additional $9.3 million of such proceeds which were included under cost of revenues in the condensed consolidated statements of operations and comprehensive income for the nine months ended September 30, 2019. The Company has filed a lawsuit against the insurers that do not accept our claim. The Company is still assessing the damages in the Puna facilities and continues to coordinate with Hawaii Electric Light Company (“HELCO”) and local authorities to bring the power plant back to operation.

As of November 2019, the reconstruction efforts at Puna are on schedule and we expect our refurbishment activities will be completed by the end of the year, enabling us to deliver energy from the plant. We expect to be able to sell the electricity produced at Puna as soon as the relevant permits required from local authorities for the operation of the substation and the transmission network upgrades being undertaken by our partners at Hawaii Electric Light Company (HELCO) are received. These are expected by the end of the first quarter of 2020, and we expect to be able to bring the power plant back to operation promptly thereafter. On the field side, we recently reached successfully the production area and have already one production well available for the operation of the power plant. In addition, we have recovered several injection wells and we continue our recovery work, which includes redrilling of existing wells, cleanouts and drilling of new wells. We expect to gradually increase the power plant’s generating capacity as we complete wellfield drilling work, with a target of regaining full operation of the power plant by the end of the second quarter of 2020.

The Company continues to assess the accounting implications of this event on the assets and liabilities on its balance sheet and whether an impairment will be required. Any significant damage to the geothermal resource or continued shut-down following the lava event at the Puna facilities could have an adverse impact on the power plant's electricity generation and availability, which in turn could have a material adverse impact on our business and results of operations.

DEG 3 Loan

On January 4, 2019, an indirect subsidiary of the Company (“OrPower 4”) entered into an additional $41.5 million subordinated loan agreement with Deutsche Investitions-und Entwicklungsgesellschaft mbH ("DEG") (the “DEG 3 Loan Agreement”) and on February 28, 2019, OrPower 4 completed a drawdown of the full loan amount, with a fixed interest rate of 6.04% for the duration of the loan (the “DEG 3 Loan”). The DEG 3 Loan will be repaid in 19 equal semi-annual principal installments commencing June 21, 2019, with a final maturity date of June 21, 2028. Proceeds of the DEG 3 Loan were used by OrPower 4 to refinance upgrades to Plant 1 of the Olkaria III Complex, which were originally financed using equity. The DEG 3 Loan is subordinated to the senior loan provided by Overseas Private Investment Corporation (“OPIC”) for Plants 1-3 of the Olkaria III Complex. The DEG 3 Loan is guaranteed by the Company.

Migdal Senior Unsecured Loan

On March 25, 2019, the Company entered into a first addendum (“First Addendum”) to the loan agreement (the "Migdal Loan Agreement") with Migdal Insurance Company Ltd., Migdal Makefet Pension and Provident Funds Ltd. and Yozma Pension Fund of Self-Employed Ltd., all entities within the Migdal Group, a leading insurance company and institutional investor in Israel dated March 22, 2018. The First Addendum provides for an additional loan by the lenders to the Company in an aggregate principal amount of $50.0 million (the “Additional Migdal Loan”). The Additional Migdal Loan will be repaid in 15 semi-annual payments of $2.1 million each, commencing on September 15, 2021, with a final payment of $18.5 million on March 15, 2029. The Additional Migdal Loan bears interest at a fixed rate of 4.6% per annum, payable semi-annually, subject to adjustment in certain circumstances as described below. The Additional Migdal Loan was entered into under substantially the same terms and conditions of the Migdal Loan Agreement as disclosed in the Company’s Form 10-K for the year ended December 31, 2018.

Exploratory Drilling Costs Capitalization and Impairment, Policy [Policy Text Block]

Write-offs of Unsuccessful Exploration Activities

There were nowrite-offs of unsuccessful exploration activities for the three and nine months ended September 30, 2019. Write-offs of unsuccessful exploration activities for the three and nine months ended September 30, 2018 were $0 and $0.1 million, respectively.

Concentration Risk, Credit Risk, Policy [Policy Text Block]

Concentration of credit risk

Financial instruments that potentially subject the Company to a concentration of credit risk consist principally of temporary cash investments and accounts receivable.

The Company places its temporary cash investments with high credit quality financial institutions located in the U.S. and in foreign countries. At September 30, 2019 and December 31, 2018, the Company had deposits totaling $47.3 million and $31.3 million, respectively, in ten U.S. financial institutions that were federally insured up to $250,000 per account. At September 30, 2019 and December 31, 2018, the Company’s deposits in foreign countries amounted to approximately $74.2 million and $93.9 million, respectively.

At September 30, 2019 and December 31, 2018, accounts receivable related to operations in foreign countries amounted to approximately $109.6 million and $102.0 million, respectively. At September 30, 2019 and December 31, 2018, accounts receivable from the Company’s primary customers amounted to approximately 59% and 56% of the Company’s accounts receivable, respectively.

Sierra Pacific Power Company and Nevada Power Company (subsidiaries of NV Energy, Inc.) accounted for 15.1% and 13.6% of the Company’s total revenues for the three months ended September 30, 2019 and 2018, respectively, and 16.7% and 15.7% of the Company’s total revenues for the nine months ended September 30, 2019 and 2018, respectively.

Southern California Public Power Authority (“SCPPA”) accounted for 16.4% and 13.7% of the Company’s total revenues for the three months ended September 30, 2019 and 2018, respectively, and 17.7% and 14.9% of the Company’s total revenues for the nine months ended September 30, 2019 and 2018, respectively.

Kenya Power and Lighting Co. Ltd. ("KPLC") accounted for 18.0% and 18.6% of the Company’s total revenues for the three months ended September 30, 2019 and 2018, respectively, and 16.6% and 16.7% of the Company’s total revenues for the nine months ended September 30, 2019 and 2018, respectively.

The Company has historically been able to collect on substantially all of its receivable balances. As of September 30, 2019, the amount overdue from KPLC in Kenya was $41.1 million of which $10.8 million was paid in October 2019. These amounts represent an average of 60 days overdue. In Honduras, there has been a deterioration in the collection from Empresa Nacional de Energía Eléctrica (“ENEE”) and as of September 30, 2019, the amount overdue is $20.1 million, none of which was paid to date. These amounts represent an average of 181 days, an increase of 73 days from June 30, 2019. Due to obligations of the Honduran government to support the Company, the Company believes it will be able to collect all past due amounts, and therefore no provision for doubtful accounts has been recorded.

Additionally, Pacific Gas and Electric Corporation (“PG&E Corporation”) and its subsidiary Pacific Gas and Electric Company (“PG&E”), which accounts for 2.2% and 1.4% of our total revenues for the three and nine months ended September 30, 2019, are facing extraordinary challenges relating to a series of catastrophic wildfires that occurred in Northern California in 2017 and 2018. As a result, on January 29, 2019, PG&E Corporation and its subsidiary, PG&E, voluntarily filed for reorganization under Chapter 11 of the U.S. Bankruptcy Code. The Company is closely monitoring its PG&E balance to ensure cash receipts are received timely each month.