IntelliJ IDEA memory usage

I am using IntelliJ IDEA on a MacBook Pro. I have configured IntelliJ with 2GB of memory. Yet when running IntelliJ with 4 or 5 decent sized projects open I see it using considerably more memory than that. IntelliJ itself reports that it is using a little more than 1GB of heap but the OS reports that it is using anywhere from 3.5 to 4.5 GB. What is using up all this memory?

Also, the java process right below IntelliJ is IntelliJ's RemoteMavenServer process.