Configuring SASS Transpiler on IntelliJ looks easy. But I couldn't quite get it to work following those steps. Here are the steps that actually works (tested on IDEA 14.1.5 on a Mac OSX El Capitan):

1. install sass: sudo gem install sass
2. go to IntelliJ IDEA | Preferences... | Plugins
3. click 'install JetBrains plugins ...'.
4. Search for File Watchers and click on "Install plugin".
5. Restart IDEA

1. go to IntelliJ IDEA | Preferences... | Editor | File Types.Find CSS Files  and add *.scss as the registered patterns

7. go to IntelliJ IDEA | Preferences... | Tools | File Watchers.
8. create a new file watcher. Fill as above. Note that this is a project specific file watcher

Alternatively, obviously you can just run a file watcher from the terminal:
sass --watch app/sass:public/stylesheets