Idaho Code § 62-103

The directors must provide a sinking fund, to be specially applied to the redemption of such bonds on or before their maturity, and may also confer on any holder of any bond or note issued, for money borrowed or in payment of any debt or contract for the construction and equipment of such road, the right to convert the principal due or owing thereon into stock of such corporation, at any time within eight (8) years from the date of such bonds, under such regulations as the directors may adopt.