Idaho Code § 5-508
When the person on whom the service is to be made resides outside of the state, or has departed from the state, or cannot after due diligence be found within the state, or conceals himself therein to avoid the service of summons, or is a foreign corporation having no managing or business agent, cashier or secretary within this state, or where any persons are made defendant by the style and description of unknown owners, or unknown heirs or unknown devisees of any deceased person and the names of such unknown owners or heirs or devisees are unknown to the complainant in the action, and such facts appear by affidavit to the satisfaction of the court in which the suit is pending, and it also appears by the affidavit or a verified complaint on file that a cause of action exists against the defendant in respect to whom the service is to be made, and that he is a necessary or proper party to the action, the court may make an order for the publication of the summons; and an affidavit setting forth in ordinary and concise language any of the grounds as above set forth, upon which the publication of the summons is sought, shall be sufficient without setting forth or showing what efforts have been made or what diligence has been exerted in attempting to find the defendant. Service upon any person, firm, company, association or corporation who is subject to the jurisdiction of the courts of this state pursuant to the provisions of section 5-514, Idaho Code, may be made in the manner provided in section 5-515, Idaho Code.
Idaho Code § 5-508