Steps to solve this are apparently made for Idea 15, Currently (August 2015) in early access.
See this comment: https://youtrack.jetbrains.com/issue/IDEABKL-5810#comment=27-1015891
You need to add the line editor.new.rendering=true
to your idea.properties
file for it to work.
I just tested it, and it seems to be working pretty well, but it is an early access.