Since Ubuntu 16.04 includes snapd
by default.
So, the easiest way to install the stable version is
$ sudo snap install intellij-idea-community --classic
$ sudo snap install intellij-idea-ultimate --classic
For the latest version use channel --edge
$ sudo snap install intellij-idea-community --classic --edge
Here is the list of all channels https://snapcraft.io/intellij-idea-ultimate (drop down 'All versions').
--classic
The --classic option is required because the IntelliJ IDEA snap requires full access to the system, like a traditionally packaged application.
[https://www.jetbrains.com/help/idea/install-and-set-up-product.html#install-on-linux-with-snaps]
--edge
--edge Install from the edge channel [http://manpages.ubuntu.com/manpages/bionic/man1/snap.1.html]
Note: Snap, also work a few major distributions: Arch, Debian, Fedora, openSUSE, Linux Mint,...