It is for Idaho residents driving Idaho-titled/registered vehicles. http://www.legislature.idaho.gov/idstat/Title49/T49CH4SECT49-456.htm
Paragraph 1 states "plates" not plate.
Then you retract your previous post where you cite that it is against the law for a NM resident to drive in Idaho without a front license plate? I will refresh your post below:
“This is like an officer in Idaho pulling someone over driving a car from New Mexico. In Idaho, two license plates are required, by law, one on the front of the vehicle, one on the back. New Mexico only requires one (on the back) and only issues one. “