Idaho Code § 20-507

Jurisdiction obtained by the court in the case of a juvenile offender shall be retained by it for the purposes of this act until he becomes twenty-one (21) years of age, unless terminated prior thereto. If a juvenile offender under the jurisdiction of the court and after attaining eighteen (18) years of age, is charged with a felony, he shall be treated as any other adult offender. If a person eighteen (18) years of age or older already under court jurisdiction is convicted of a felony, that conviction shall terminate the jurisdiction of the court, provided however, nothing herein contained shall prohibit any court from proceeding as provided in section 20-508(2), Idaho Code.