Commitments And Contingencies	12 Months Ended
Commitments And Contingencies	Sep. 30, 2025
Commitments and Contingencies Disclosure [Abstract]
Commitments And Contingencies	Commitments and Contingencies Purchase Obligations In October 2022, the Company entered into an unconditional purchase commitment with one of its suppliers for the delivery of systems components. Under the terms of the agreement, the Company is obligated to purchase $10 million of component inventory annually, with a total committed amount of $40 million over a four-year term. As of September 30, 2025, the Company had no remaining purchase commitments under the third year of the agreement. The Company's total non-cancelable long-term purchase commitments outstanding as of September 30, 2025 was $10.0 million. Litigation Lynwood Investment CY Limited v. F5 Networks et al. On June 8, 2020, Lynwood Investment CY Limited ("Lynwood") filed a lawsuit in the United States District Court for the Northern District of California ("District Court") against the Company and certain affiliates, along with other defendants. In its complaint, Lynwood claims to be the assignee of all rights and interests of Rambler Internet Holding LLC ("Rambler"), and alleges that the intellectual property in the NGINX software originally released by the co-founder of NGINX in 2004 belongs to Rambler (and therefore Lynwood, by assignment) because the software was created and developed while the co-founder was employed by Rambler. Lynwood asserted 26 causes of action against the various defendants, including copyright infringement, violation of trademark law, tortious interference, conspiracy, and fraud. The complaint sought damages, disgorgement of profits, declarations of copyright and trademark ownership, trademark cancellations, and injunctive relief. Lynwood also initiated several trademark opposition and cancellation proceedings before the Trademark Trial and Appeal Board of the United States Patent and Trademark Office, which have all since been suspended. In August and October 2020, the Company and the other defendants filed motions to dismiss Lynwood’s case. On March 25 and 30, 2021, the District Court granted the Company’s and the other defendants’ motions to dismiss with leave to amend. Lynwood filed its amended complaint on April 29, 2021, seeking the same relief against the Company and other defendants. On May 27, 2021, the Company and other defendants filed a consolidated motion to dismiss. The District Court granted the consolidated motion to dismiss without leave to amend on August 16, 2022 and entered final judgment against Lynwood on September 9, 2022. Following the District Court’s order granting the consolidated motion to dismiss and final judgment in the Company’s favor, the District Court subsequently granted the Company attorneys' fees of over $0.8 million, which Lynwood appealed to the Ninth Circuit Court of Appeals. The dismissal appeal and the fees appeal were heard by the Ninth Circuit Court of Appeals ("Court of Appeals") on December 7, 2023. On November 7, 2024, the Court of Appeals partially affirmed the dismissal by affirming dismissal of the state law claims and remanding a portion of the copyright claim to the District Court. The Court of Appeals also vacated the fees award because of the remand. On December 2, 2024, the Court of Appeals issued its mandate returning the matter to the District Court for further proceedings on the remaining portion of the copyright claim. The parties are engaged in a first phase of discovery ordered by the Court in a March 7th case management conference that is focused on whether any NGINX Plus code was written by individuals employed by Rambler before the end of 2011. On May 19, 2025, the Company and the other defendants answered Lynwood’s second amended complaint filed April 7, 2025, which was limited to the remaining portion of the copyright claim focused on NGINX Plus per the Court’s March 7th order. The Company intends to continue vigorously defending the litigation. In addition to the above matters, the Company is subject to a variety of legal proceedings, claims, investigations, and litigation arising in the ordinary course of business, including intellectual property litigation. Management believes that the Company has meritorious defenses to the allegations made in its pending cases and intends to vigorously defend these lawsuits; however, the Company is unable to currently determine if an unfavorable outcome is probable or estimate any potential amount or range of possible loss of these or similar matters. There are many uncertainties associated with any litigation and these actions or other third-party claims against the Company may cause it to incur costly litigation and/or substantial settlement charges that could have a material adverse effect on the Company's business, financial condition, results of operations, and cash flows. The Company records an accrual for loss contingencies for legal proceedings when it believes that an unfavorable outcome is both (a) probable and (b) the amount or range of any possible loss is reasonably estimable. The Company has not recorded any accrual for loss contingencies associated with such legal proceedings or the investigations discussed above. Cyber Incident On October 15, 2025, we disclosed a security incident in which a threat actor maintained long-term, persistent access to F5 systems, and certain files were exfiltrated, referred to as the "Cyber Incident." In connection with the Cyber Incident, some customers and third parties may assert claims against the Company and or officers and directors of the Company. The Company has also received a small number of inquiries from governmental authorities. The Company is cooperating and providing information in connection with these inquiries. The Company may incur significant legal and professional services and other expenses associated with the incident in future periods. These expenses will be recognized as incurred. Certain costs may be recoverable under the Company’s insurance policies. Any amounts recoverable under such policies will be reflected in future periods in which recovery is considered probable. To date, such costs related to the incident are not material.