In short this bill states the following:

A landlord who collects and holds a security deposit on and after July
20 1, 2010, for a period of one (1) year or longer shall pay to the tenant
interest on the deposit at a rate equal to the interest rate paid on regular
savings accounts in the Idaho bank, savings and loan association, or credit
union in which it is deposited, commencing from the date the landlord
receives the deposit. If a landlord mingles security deposits in a single
account the landlord shall pay the actual interest earned on such account
proportionately to each tenant. A tenant may request the interest accrued on
a security deposit every year, thirty (30) days before the expiration of that
year’s tenancy. The landlord shall comply with the request within fifteen
(15) days of the expiration of that year’s tenancy.
Refunds, including the interest due, if any, shall be made within
Twenty-one (21) days if no time is fixed by agreement, and in any event,
within thirty (30) days after surrender of the premises by the tenant.