Idaho Code § 42-3112
If there is a vacancy of any commissioner position through death, resignation, failure to meet the qualification requirements of section 42-3111, Idaho Code, or removal by the director, such vacancy shall be filled by appointment by the remaining members or member of the board. Said appointee shall be a resident of the same division of the district as the commissioner whom he is replacing and shall serve for the unexpired term, or until his successor is appointed and qualified, except that, in the event the board is unable to appoint a resident of the division vacated, the board may appoint a person at-large who is a qualified elector of the district pursuant to section 42-3118, Idaho Code, to serve as commissioner of the division where the vacancy occurred. If the board fails to fill a vacancy, or if there are no members of the board due to vacancies, the director may make such appointments to represent each division of the district.
Idaho Code § 42-3112