Is it illegal to ride in the back of a pick up truck in Idaho?

"Washington does not have a law that prevents persons from riding in pickup beds. However, the seat belt law does require that all passenger positions with safety belts be utilized. Example: If there are five seating positions in the pickup and there are only two adults in the passenger compartment but three other persons in the pickup bed, the driver (depending on the age of the persons in the pickup bed) could be issued a Notice of Infraction." From the Washington state Patrol FAQ http://www.wsp.wa.gov/newsfaqs/faqs.htm