Idaho Code § 50-608

In case of a temporary vacancy in the office of mayor due to absence or disability, the president of the council shall exercise the office of mayor during such disability or temporary absence, and until the mayor shall return. When a vacancy occurs in the office of mayor by reason of death, resignation or permanent disability, the city council shall fill the vacancy from within or without the council as may be deemed in the best interests of the city, which appointee shall serve until the next general city election, at which election a mayor shall be elected for the full four (4) year term.