Commitments and Contingencies	6 Months Ended
Jun. 30, 2026
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies Contingencies Self-Funding of Transmission Upgrades for Generator Interconnections. The Federal Energy Regulatory Commission (FERC) has granted transmission owners within Midcontinent Independent System Operator, Inc. (MISO) and other regional transmission organizations (RTOs) the unilateral authority to determine the funding mechanism for interconnection transmission upgrades that are necessary to accommodate new generation facilities connecting to the electrical grid. Under existing FERC orders, transmission owners can unilaterally determine whether the generator pays the transmission owner in advance for the transmission upgrade or, alternatively, the transmission owner can elect to fund the upgrade and recover over time from the generator the cost of and a return on the upgrade investment (a self-funding). FERC’s orders granting transmission owners this unilateral funding authority have been judicially contested on the basis that transmission owners may be motivated to discriminate among generators in making funding determinations. In the most recent judicial proceedings, the petitioners argued to the U.S. Court of Appeals for the District of Columbia that FERC did not comply with a previous judicial order to fully develop a record regarding the risk of discrimination and the financial risk absorbed by transmission owners for generator-funded upgrades. In December 2022, the Court of Appeals ruled in favor of the petitioners remanding the matter to FERC, instructing the agency to adequately explain the basis of its orders. The Court of Appeals decision did not vacate the transmission owners’ unilateral funding authority. In June 2024, FERC issued an Order to Show Cause proceeding against four RTOs, including MISO. Within its order, FERC indicates that the transmission tariffs of the RTOs appear to be unjust, unreasonable, and unduly discriminatory or preferential because they allow transmission owners to unilaterally elect transmission owner self-funding, which may increase costs, impose barriers to transmission interconnection and result in undue discrimination among interconnection customers. The order required each RTO to submit filings to either 1) show cause as to why the transmission tariff remains just and reasonable and not duly discriminatory or preferential, or 2) to explain what changes to the tariff it believes would remedy the identified concerns. FERC has received a number of responses to its Order to Show Cause. In September 2024, in separate filings, MISO and transmission owners within MISO, including OTP, filed responses outlining the reasons why the self-funding option remains just and reasonable and not unduly discriminatory or preferential. Other responses have been provided by other RTOs, individual transmission owners, developers of renewable generation facilities and other interested parties. OTP, as a transmission owner in MISO, has exercised its authority and elected to self-fund transmission upgrades necessary to accommodate new system generation. Under such an election, OTP is recovering the cost of the transmission upgrade and a return on that investment from the generator over a contractual period of time. Should the resolution of this matter eliminate transmission owners’ unilateral funding authority on either a prospective or retrospective basis, our financial results would be impacted. We cannot at this time reasonably predict the outcome of this matter given the uncertainty as to how FERC may ultimately decide on the matter. Class Action Lawsuits and Related Matters. Beginning in August of 2024, a series of putative federal class action lawsuits, now consolidated under the caption In re: PVC Pipe Antitrust Litigation (Case No. 1:24-cv-07639), were filed in the United States District Court for the Northern District of Illinois against Northern Pipe Products, Vinyltech Corporation, Otter Tail Corporation and more than twenty other PVC pipe manufacturers, as well as Oil Price Information Systems, LLC (OPIS), a reporting service that provides pricing and market information in various industries, including the PVC pipe industry during the relevant period. The Court permitted plaintiffs to proceed through three putative class complaints: a Direct Purchaser Class (DPPs), a Non-Converter Seller Purchaser Class (NCSPs) and an End-User Class (EUPs). In August of 2025, the three putative classes each filed a first or an amended complaint alleging, among other things, that the defendants and alleged co-conspirators conspired to fix, raise, maintain and stabilize the price of PVC municipal pipe, PVC plumbing pipe, PVC electrical pipe and PVC pipe fittings in violation of U.S. federal and state antitrust laws. The complaints alleged that PVC pipe manufacturers improperly exchanged confidential information through OPIS and engaged in other indirect and direct communications with each other. The plaintiffs were seeking treble damages, injunctive relief, pre- and post-judgment interest, costs and attorneys' fees on behalf of the putative classes. On May 28, 2026, the Company entered into settlement agreements with the DPPs and NCSPs, individually and on behalf of the putative DPP and NCSP class members. Subject to the satisfaction of certain conditions, the Company’s subsidiaries, Northern Pipe Products, Inc. and Vinyltech Corporation, agreed to pay $39.5 million to resolve all claims asserted, or that could have been asserted, by the DPPs against the Company, and $34.0 million to resolve all claims asserted, or that could have been asserted, by the NCSPs against the Company, in each case relating to the alleged conduct at issue in the PVC pipe antitrust litigation. During the second quarter of 2026, Northern Pipe Products and Vinyltech Corporation paid an aggregate amount of $73.5 million into settlement fund escrow accounts utilizing available cash. As of June 30, 2026, the $73.5 million was included as restricted cash on our consolidated balance sheet pending the final court approval of the DPP and NCSP settlement agreements. On June 17, 2026, the Company entered into a settlement agreement with the EUPs, individually and on behalf of the putative class members. Subject to the satisfaction of certain conditions, the Company’s subsidiaries, Northern Pipe Products, Inc. and Vinyltech Corporation, agreed to pay $30.0 million to resolve all claims asserted, or that could have been asserted, by the EUPs against the Company, relating to the alleged conduct at issue in the PVC pipe antitrust litigation. In July 2026, Northern Pipe Products and Vinyltech Corporation paid $30.0 million into a settlement fund escrow account utilizing available cash. The amount will be reflected as restricted cash on our consolidated balance sheet pending final court approval of the settlement agreement. The settlement agreements remain subject to the satisfaction of certain conditions, including final approval by the Court. Following preliminary approval of each settlement by the Court, the settlement administrators began notice campaigns to inform potential class members of the settlements and advise them of their right to request exclusion from, or opt out of the applicable settlement. To be valid, exclusion requests must be received before the end of the applicable notice period. The NCSP notice period ends August 7, 2026, the DPP notice period ends August 25, 2026, and the EUP notice period ends September 8, 2026. The DPP and NCSP settlement agreements contain provisions allowing the Company to terminate the respective settlement agreement if opt outs exceed certain thresholds. In connection with the class action lawsuits in the United States, we have recognized an estimated loss in the amount of $103.5 million, which was included in other current liabilities on our consolidated balance sheet as of June 30, 2026. The execution of the settlement agreements does not constitute an admission by the Company of any wrongdoing, fault, or liability, and the Company does not admit any wrongdoing, fault, or liability. Although the Company believes it has factual and legal defenses and was prepared to continue litigating, the Company determined that resolving these claims was in its best interests. The settlements meaningfully reduce the uncertainty, distraction, and potential costs and exposure associated with protracted and complex class action antitrust litigation and allow the Company to maintain its focus on executing its business strategy. On September 26, 2025, a putative nation-wide class action complaint (Case No. S-257310) was filed in the Supreme Court of British Columbia, Canada against Northern Pipe, Vinyltech Corporation, Otter Tail Corporation and several other PVC pipe manufacturers, as well as OPIS. The complaint alleges that the defendants conspired to fix, raise, maintain, and stabilize the price of PVC pipe through an information exchange, OPIS, breaching Canada's Competition Act. The plaintiffs seek general damages, injunctive relief, pre- and post-judgment interest, punitive damages, costs, and attorneys' fees on behalf of the putative class. The Company believes there are factual and legal defenses to the allegations in the complaint and is defending itself accordingly. In August 2024, the Company received a grand jury subpoena issued by the U.S. District Court for the Northern District of California, from the U.S. Department of Justice (DOJ) Antitrust Division. The subpoena calls for production of documents regarding the manufacturing, selling and pricing of PVC pipe. The Company has responded to the subpoena and intends to comply with its obligations thereunder. On October 7, 2025, the DOJ filed a motion to intervene and for a partial stay of document discovery in In Re: PVC Pipe Antitrust Litigation. On July 1, 2026, the DOJ moved to extend the discovery stay until December 31, 2026, and narrow the terms of the stay. As it pertains to the unresolved complaint in Canada and the DOJ investigation, the Company believes there are factual and legal defenses and is defending itself accordingly. There remains considerable uncertainty regarding the timing or ultimate resolution of the litigation in Canada and the DOJ investigation. At this time, we are unable to determine the likelihood of an outcome or estimate a range of reasonably possible losses, if any, arising from these matters. The resolution of these matters could have a material impact on the Company’s financial position, operating results and liquidity, and it is reasonably possible that our assessment of losses arising from these matters could change in the near term. On May 20, 2025, the Otter Tail Corporation Board of Directors received a letter from counsel submitted on behalf of a shareholder, demanding the Board investigate and take legal action against certain current and former directors and officers of the Company. The derivative demand letter alleges securities law violations, breaches of fiduciary duties, and unjust enrichment by certain current and former officers and directors of the Company in connection with the matters at issue in the pending civil antitrust cases. At this time, we are unable to determine the likelihood of any outcome related to this matter. Other Contingencies. We are involved in claims, legal proceedings, investigations and regulatory matters arising in the normal course of business. We regularly analyze relevant information and, as necessary, estimate and record accrued liabilities for legal, regulatory enforcement and other matters in which a loss or range of loss is probable of occurring and can be reasonably estimated. We believe the effect on our consolidated operating results, financial position and cash flows, if any, for the disposition of all matters pending as of June 30, 2026, other than those discussed above, will not be material.

Self-Funding of Transmission Upgrades for Generator Interconnections. The Federal Energy Regulatory Commission (FERC) has granted transmission owners within Midcontinent Independent System Operator, Inc. (MISO) and other regional transmission organizations (RTOs) the unilateral authority to determine the funding mechanism for interconnection transmission upgrades that are necessary to accommodate new generation facilities connecting to the electrical grid. Under existing FERC orders, transmission owners can unilaterally determine whether the generator pays the transmission owner in advance for the transmission upgrade or, alternatively, the transmission owner can elect to fund the upgrade and recover over time from the generator the cost of and a return on the upgrade investment (a self-funding). FERC’s orders granting transmission owners this unilateral funding authority have been judicially contested on the basis that transmission owners may be motivated to discriminate among generators in making funding determinations. In the most recent judicial proceedings, the petitioners argued to the U.S. Court of Appeals for the District of Columbia that FERC did not comply with a previous judicial order to fully develop a record regarding the risk of discrimination and the financial risk absorbed by transmission owners for generator-funded upgrades. In December 2022, the Court of Appeals ruled in favor of the petitioners remanding the matter to FERC, instructing the agency to adequately explain the basis of its orders. The Court of Appeals decision did not vacate the transmission owners’ unilateral funding authority.

In June 2024, FERC issued an Order to Show Cause proceeding against four RTOs, including MISO. Within its order, FERC indicates that the transmission tariffs of the RTOs appear to be unjust, unreasonable, and unduly discriminatory or preferential because they allow transmission owners to unilaterally elect transmission owner self-funding, which may increase costs, impose barriers to transmission interconnection and result in undue discrimination among interconnection customers.

The order required each RTO to submit filings to either 1) show cause as to why the transmission tariff remains just and reasonable and not duly discriminatory or preferential, or 2) to explain what changes to the tariff it believes would remedy the identified concerns. FERC has received a number of responses to its Order to Show Cause. In September 2024, in separate filings, MISO and transmission owners within MISO, including OTP, filed responses outlining the reasons why the self-funding option remains just and reasonable and not unduly discriminatory or preferential. Other responses have been provided by other RTOs, individual transmission owners, developers of renewable generation facilities and other interested parties.

OTP, as a transmission owner in MISO, has exercised its authority and elected to self-fund transmission upgrades necessary to accommodate new system generation. Under such an election, OTP is recovering the cost of the transmission upgrade and a return on that investment from the generator over a contractual period of time. Should the resolution of this matter eliminate transmission owners’ unilateral funding authority on either a prospective or retrospective basis, our financial results would be impacted. We cannot at this time reasonably predict the outcome of this matter given the uncertainty as to how FERC may ultimately decide on the matter.

Class Action Lawsuits and Related Matters. Beginning in August of 2024, a series of putative federal class action lawsuits, now consolidated under the caption In re: PVC Pipe Antitrust Litigation (Case No. 1:24-cv-07639), were filed in the United States District Court for the Northern District of Illinois against Northern Pipe Products, Vinyltech Corporation, Otter Tail Corporation and more than twenty other PVC pipe manufacturers, as well as Oil Price Information Systems, LLC (OPIS), a reporting service that provides pricing and market information in various industries, including the PVC pipe industry during the relevant period. The Court permitted plaintiffs to proceed through three putative class complaints: a Direct Purchaser Class (DPPs), a Non-Converter Seller Purchaser Class (NCSPs) and an End-User Class (EUPs).

In August of 2025, the three putative classes each filed a first or an amended complaint alleging, among other things, that the defendants and alleged co-conspirators conspired to fix, raise, maintain and stabilize the price of PVC municipal pipe, PVC plumbing pipe, PVC electrical pipe and PVC pipe fittings in violation of U.S. federal and state antitrust laws. The complaints alleged that PVC pipe manufacturers improperly exchanged confidential information through OPIS and engaged in other indirect and direct communications with each other. The plaintiffs were seeking treble damages, injunctive relief, pre- and post-judgment interest, costs and attorneys' fees on behalf of the putative classes.

On May 28, 2026, the Company entered into settlement agreements with the DPPs and NCSPs, individually and on behalf of the putative DPP and NCSP class members. Subject to the satisfaction of certain conditions, the Company’s subsidiaries, Northern Pipe Products, Inc. and Vinyltech Corporation, agreed to pay $39.5 million to resolve all claims asserted, or that could have been asserted,

by the DPPs against the Company, and $34.0 million to resolve all claims asserted, or that could have been asserted, by the NCSPs against the Company, in each case relating to the alleged conduct at issue in the PVC pipe antitrust litigation. During the second quarter of 2026, Northern Pipe Products and Vinyltech Corporation paid an aggregate amount of $73.5 million into settlement fund escrow accounts utilizing available cash. As of June 30, 2026, the $73.5 million was included as restricted cash on our consolidated balance sheet pending the final court approval of the DPP and NCSP settlement agreements.

On June 17, 2026, the Company entered into a settlement agreement with the EUPs, individually and on behalf of the putative class members. Subject to the satisfaction of certain conditions, the Company’s subsidiaries, Northern Pipe Products, Inc. and Vinyltech Corporation, agreed to pay $30.0 million to resolve all claims asserted, or that could have been asserted, by the EUPs against the Company, relating to the alleged conduct at issue in the PVC pipe antitrust litigation. In July 2026, Northern Pipe Products and Vinyltech Corporation paid $30.0 million into a settlement fund escrow account utilizing available cash. The amount will be reflected as restricted cash on our consolidated balance sheet pending final court approval of the settlement agreement.

The settlement agreements remain subject to the satisfaction of certain conditions, including final approval by the Court. Following preliminary approval of each settlement by the Court, the settlement administrators began notice campaigns to inform potential class members of the settlements and advise them of their right to request exclusion from, or opt out of the applicable settlement. To be valid, exclusion requests must be received before the end of the applicable notice period. The NCSP notice period ends August 7, 2026, the DPP notice period ends August 25, 2026, and the EUP notice period ends September 8, 2026. The DPP and NCSP settlement agreements contain provisions allowing the Company to terminate the respective settlement agreement if opt outs exceed certain thresholds.

The execution of the settlement agreements does not constitute an admission by the Company of any wrongdoing, fault, or liability, and the Company does not admit any wrongdoing, fault, or liability. Although the Company believes it has factual and legal defenses and was prepared to continue litigating, the Company determined that resolving these claims was in its best interests. The settlements meaningfully reduce the uncertainty, distraction, and potential costs and exposure associated with protracted and complex class action antitrust litigation and allow the Company to maintain its focus on executing its business strategy.

On September 26, 2025, a putative nation-wide class action complaint (Case No. S-257310) was filed in the Supreme Court of British Columbia, Canada against Northern Pipe, Vinyltech Corporation, Otter Tail Corporation and several other PVC pipe manufacturers, as well as OPIS. The complaint alleges that the defendants conspired to fix, raise, maintain, and stabilize the price of PVC pipe through an information exchange, OPIS, breaching Canada's Competition Act. The plaintiffs seek general damages, injunctive relief, pre- and post-judgment interest, punitive damages, costs, and attorneys' fees on behalf of the putative class. The Company believes there are factual and legal defenses to the allegations in the complaint and is defending itself accordingly.

In August 2024, the Company received a grand jury subpoena issued by the U.S. District Court for the Northern District of California, from the U.S. Department of Justice (DOJ) Antitrust Division. The subpoena calls for production of documents regarding the manufacturing, selling and pricing of PVC pipe. The Company has responded to the subpoena and intends to comply with its obligations thereunder. On October 7, 2025, the DOJ filed a motion to intervene and for a partial stay of document discovery in In Re: PVC Pipe Antitrust Litigation. On July 1, 2026, the DOJ moved to extend the discovery stay until December 31, 2026, and narrow the terms of the stay.

As it pertains to the unresolved complaint in Canada and the DOJ investigation, the Company believes there are factual and legal defenses and is defending itself accordingly. There remains considerable uncertainty regarding the timing or ultimate resolution of the litigation in Canada and the DOJ investigation. At this time, we are unable to determine the likelihood of an outcome or estimate a range of reasonably possible losses, if any, arising from these matters. The resolution of these matters could have a material impact on the Company’s financial position, operating results and liquidity, and it is reasonably possible that our assessment of losses arising from these matters could change in the near term.

On May 20, 2025, the Otter Tail Corporation Board of Directors received a letter from counsel submitted on behalf of a shareholder, demanding the Board investigate and take legal action against certain current and former directors and officers of the Company. The derivative demand letter alleges securities law violations, breaches of fiduciary duties, and unjust enrichment by certain current and former officers and directors of the Company in connection with the matters at issue in the pending civil antitrust cases. At this time, we are unable to determine the likelihood of any outcome related to this matter.

Other Contingencies. We are involved in claims, legal proceedings, investigations and regulatory matters arising in the normal course of business. We regularly analyze relevant information and, as necessary, estimate and record accrued liabilities for legal, regulatory enforcement and other matters in which a loss or range of loss is probable of occurring and can be reasonably estimated. We believe the effect on our consolidated operating results, financial position and cash flows, if any, for the disposition of all matters pending as of June 30, 2026, other than those discussed above, will not be material.