I just fixed this problem.

In my ~/.idlerc/ folder there was no `config-main.cfg` so I created it and used the settings found here: https://svn.python.org/projects/python/trunk/Mac/IDLE/config-main.def

After doing that everything worked fine again.

I'm not sure where this bug came from though, whether it's my package manager, or some bug in IDLE itself that created this problem; I also don't know if this is normal behavior for a missing config file; so I do n't know whether to close this or not, so I'll leave that to you.