Idaho Code § 15-3-102
Except as provided in section 15-3-1201 of this code, to be effective to prove the transfer of any property or to nominate an executor, a will must be declared to be valid by an order of informal probate by the registrar, or an adjudication of probate by the court, except that a duly executed and unrevoked will which has not been probated may be admitted as evidence of a devise if (1) no court proceeding concerning the succession or administration of the estate has occurred, and (2) either the devisee or his successors and assigns possessed the property devised in accordance with the provisions of the will, or the property devised was not possessed or claimed by anyone by virtue of the decedent's title during the time period for testacy proceedings.
Idaho Code § 15-3-102