Idaho Code § 49-2421
The operation by any person, either as principal, master, agent, servant or otherwise, of any motor vehicle, whether registered or unregistered, and with or without a license to operate, on any highway in this state, shall be deemed equivalent to an appointment by that person of the secretary of state to be his true and lawful attorney, upon whom may be served all lawful summons and processes in any action or proceeding against him, growing out of any accident or collision in which he, either as principal, master, agent, servant, or otherwise, may be involved while operating, causing or permitting the operation of a motor vehicle upon a highway. The operation shall be signification of an agreement by the person that any summons or process against him which is so served shall be of the same legal force and validity as if served on him personally within Idaho. Service of the processes shall be made by leaving a copy of the process, with a fee of five dollars ($5.00), in the hands of the secretary of state or in his office. The service shall be a sufficient and valid personal service upon that person; provided, notice of the service and a copy of the process is sent by registered mail by the plaintiff to the defendant, and the defendant's return receipt and plaintiff's affidavit of compliance are appended to the process and entered as a part of the return. Personal service outside of the state in accordance with the provisions of the laws of Idaho relating to personal service of summons outside of the state shall relieve a plaintiff from mailing copies of the summons or process by registered mail as provided in this section. Service of the process upon a defendant shall not be complete until it is either made by registered mail or by personal service outside of the state. The court in which the action is brought may order continuances as may be necessary to afford the defendant reasonable opportunity to defend the action.
Idaho Code § 49-2421