Idaho Code § 19-1711: Objections must be taken by demurrer.

When the objections declared grounds of demurrer by this chapter appear upon the face of the indictment, they can only be taken by demurrer, except that the objections to the jurisdiction of the court over the subject of the indictment, or that the facts stated do not constitute a public offense, may be taken at the trial under the plea of not guilty, or after the trial in arrest of judgment.