Intellij Idea is an advanced and mature IDE capable of supporting an ever impressive list of languages.
With Idea being based on Java it is cross platform and runs on linux, mac and windows.
IntelliJ IDEA has a Haxe plugin which is take advantage of the robust and mature environment of IDEA.
There are many things about the IDE that are of benefit to any language you use idea for, such as amazing Version Control Integration, advanced code refactoring, sdk and library management, code completion/generation, code analysis, flash debugging, code formatting, color themes and the list goes on.
The Haxe Plugin currently has a dependency of the "Ultimate" version of Idea which is a paid for commercial app. IntelliJ IDEA Ultimate are provided with the 30 days trial period. There is also an opensource "Community" edition that has great Android/Java support.
Jetbrains have a very active issue tracker where Haxe issues/features etc are being taken monitored by the hard working devs.