Idaho Code § 63-3041: Overpayments.

If the taxpayer has paid more than the amount determined to be the correct amount of the tax, the excess shall be credited or refunded as provided in section 63-3072, Idaho Code, as amended. In the event a joint return has been filed and one (1) spouse dies prior to issuance of credit or refund, the credit or refund may be granted the surviving spouse. In the event a joint return has been filed by a couple separated after filing of the return, the credit or refund may be equally divided between such persons unless a joint claim has theretofore been properly executed.