Directors shall be elected by the members of a domestic mutual insurer at the annual meeting of members. Directors may be elected for terms of not more than five years each and until their successors are elected and have qualified, and if to be elected for terms of more than one year, the insurer’s bylaws shall provide for a staggered term system under which the terms of a proportionate part of the number of the board of directors shall expire on the date of each annual meeting of members.