How to dress to attend the ballet?

I'm going to the ballet that my university is putting on. It's an 8pm show if that makes a difference. I was planning on wearing a nice black dress (not like a prom dress, but more like a semi-formal dress) and heels and maybe a sweater if I can find one in time (it's cold here and I left my nice coat at home on break). Is this overdressed? If so, what do you suggest?