You can change also be more specific and change the behavior for only IntelliJ with the following command. The -g option in the above solution changes it for all applications.
defaults write com.jetbrains.intellij ApplePressAndHoldEnabled -bool false
For the 14.x community edition, you may need to use a different URI:
defaults write com.jetbrains.intellij.ce ApplePressAndHoldEnabled -bool false
This works for MacOSX 10.10 Yosemite and IntelliJ 13.1.6