Idaho Code § 59-1321
A political subdivision not participating in the system may, through its governing body, notify the board in writing that it elects to include its employees in the system. The board shall make a study and estimate the cost of including such employees in the system. Upon completion of the study and under the condition that the excess cost, if any, to include the employees as active members is paid upon admission, the political subdivision may apply for admission to the system. Payment of excess cost shall be made upon admission, unless the board in its sole discretion grants an extension. In no case shall an extension exceed two (2) years. Thereupon the board may upon such terms, not inconsistent with this chapter, as are set forth in a contract between the board and the political subdivision, integrate said political subdivision, and its employees into the system established by this chapter effective on the date of notice of election or later unless otherwise prohibited by law. The contract shall have no effect, however, until notice and hearing regarding it is afforded to such employees. Such contract shall provide for the appropriate funding of accrued benefits under any existing retirement program at the time the political subdivision is admitted to the system.
Idaho Code § 59-1321