I'm using IntelliJ IDEA on Arch Linux with KDE. OpenJDK version is 1.7.0_40.
Whole IDE fonts (includes code editor) are rendered without any antialiasing and font smoothing. I set in idea.properties file idea.use.default.antialiasing.in.editor to true, and added in _JAVA_OPTIONS variable -Dawt.useSystemAAFontSettings=on -Dswing.aatext=true without any effect.
What else I can try to enable font smoothing?

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
pacman -S base-develand 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
This will make intelliJ run in the ORACLE JVM rather than the OpenJDK one, which fixes the font issues all together.