Does anyone know what this piece is called on my '92 Mazda Miata?

I recently got a '92 Mazda Miata really cheap as my first car. It runs perfectly and only has some cosmetic problems. One of these problems is a broken piece above the rear bumper. It surrounds the license plate and trunk door key hole and goes from tail light to tail light. It's just above the bumper and it doesn't appear to be actually attached to the bumper itself. Does anyone know what this piece is called and have an estimate on how much it costs? If it is a part of the bumper, is there any way I could purchase it separately?