SBT sources in IDEA

In SBT there are two command which may interest you:

update-classifiers - will download all sources and documentation for all libs in your project
update-sbt-classifiers - downloads sbt sources and docs

This will download all the sources you need. To make an IDEA project with them just call gen-idea sbt-classifiers.

If you don't want to call each time this commands for re-generating you project, you should add something like this to your build.sbt: addCommandAlias("make-idea", ";update-classifiers; update-sbt-classifiers; gen-idea sbt-classifiers").

As of sbt version 1.2.8, the command is changed to:
sbt updateClassifiers - to download all sources and docs
sbt updateSbtClassifiers - to download sbt sources and docs.