You don't have to use Eclipse to do assignments at https://www.coursera.org/course/progfun
How to use IDEA? It's easy!
Create a file ~/.sbt/plugins/build.sbt and put this there
addSbtPlugin("com.github.mpeltonen" % "sbt-idea" % "1.5.1")
Open sbt in your assignment folder and run
To install scala plugin in IDEA: Settings/Preferences -> Plugins -> Browse repositories -> find Scala, right click -> Download and Install. Restart IDEA
Open the folder with your assignment in IDEA: File -> Open Project...
You don't have to buy the Ultimate version. Community edition works fine, it's open source and free.