Idaho Code § 32-709: Modification of provisions for maintenance and support.

(1) The provisions of any decree respecting maintenance or support may be modified only as to installments accruing subsequent to the motion for modification and only upon a showing of a substantial and material change of circumstances.

(2) The court may allow a credit against child support arrearages for periods of time exceeding one hundred twenty (120) days during which the minor children have lived primarily with the obligated parent with the knowledge and consent of the custodial parent.