Idaho R. App. P. 7.1
Any person or entity who is a real party in interest to an appeal or proceeding governed by these rules or whose interest would be affected by the outcome of an appeal or proceeding under these rules may file a verified petition with the Supreme Court asking for leave to intervene as a party to the appeal or proceeding and serve a copy thereof upon all parties to the appeal or proceeding. The petition shall be processed as a motion in accordance with Rule 32 of these rules, and if the Supreme Court finds that such petitioning person or entity is a real party in interest or would be affected by the outcome of the appeal or proceeding, the Court may, in its discretion, grant leave to the petitioning party to intervene as a party appellant or respondent; and if leave is so granted such petitioning party shall thereafter be a party to the appeal or proceedings for all purposes under these rules.
Id. App. R. 7.1