Seems a little high for idle temps, but that might be expected considering you're running in an MITX case.... can you open the case and verify that your fan is spinning?
You should probably open Precision X or Afterburner and play with your fan curves a bit, I set mine to where the fan runs at 10% higher speed than what the temp reading is, so if my temps are 40C, my fan is running at 50%, this brings temps down really fast.
 
Edit: I just looked at your case on Newegg, it really doesn't appear that the graphics card gets much airflow in that case, so I think we can explain your higher than average idle temps.... unless I'm wrong, you really might want to consider another case, not a good idea to starve a 780 for air.
 
Edit2: Heh actually nevermind, just watched a review of that case on youtube, it has two fans feeding the graphics card on the side/bottom, I'd definitely recommend running the case vertically instead of horzontally..... it doesn't look like like the feet are high enough to allow good airflow in the horizontal config.

I would've never guessed the fan actually wasn't spinning considering those temps, I thought at worst you had a bad fan sensor and less than optimal airflow o.O

One thing you could try before starting the RMA process.... open up prceision X and manually set your fan up to 100%... believe me, you'll hear it if it works..... might be just enough to kickstart that fan and get it working properly.

Just gave that a try. On opening the app, the fan was already at 100%. Setting it to 0% and back to 100% did nothing. Looks like it's hardware related. GPU is now idle at 36C though. Not sure I trust that figure.

Hello HushedAssassin
 
 
I have sent you a email on this issue in order to support you with a RMA request.

Nice to see the fast response GabrielIT.