This is a known bug in OpenJDK. I don't think any amount of tweaking will fix this for you, it might make it a bit better, but the font rendering is broken in OpenJDK.
The most pain free fix IMHO, is to go to the AUR and install jdk7-compat, which is designed to run next to your normal JDK.
Don't worry if you never used the AUR, its really straight forward. Basically, what you do is
- insure you have base-devel installed with
pacman -S base-devel
- download the tar from the AUR page I linked above, uncompress it.
- run 'makepkg -di' in the folder where you uncompressed to
and its done. Now, edit /usr/share/intellijidea-ce/bin/idea.sh and change the line which executes the program (its in the bottom of the file) so it looks like this
eval "/opt/java7/bin/java" $ALL_JVM_ARGS -Djb.restart.code=88 $MAIN_CLASS_NAME "$@"
This will make intelliJ run in the ORACLE JVM rather than the OpenJDK one, which fixes the font issues all together.