Idaho Code § 26-806
It shall be unlawful for any bank to pledge, mortgage or hypothecate to any depositor any of its real or personal property as security for any deposit except money of the United States, the state of Idaho and its political subdivisions, and deposits for which security is required by any law of the United States, or required or permitted by any other statute of this state. Any pledge, mortgage or hypothecation made in violation hereof shall be unenforceable and void and any person, firm or corporation, holding or receiving any security or securities mortgaged or hypothecated, pledged or attempted to be pledged, shall, upon demand of any officer, director or stockholder of the bank or the director, be required forthwith to make return thereof, and the repayment of any deposit shall not be prerequisite to the recovery of any property so unlawfully pledged, hypothecated or mortgaged.
Idaho Code § 26-806