There are a few ways to set this up, The easiest is to run th;e game in a "screen" session. You have to install "screen" on the box first.
http://www.gnu.org/software/screen/screen.html
Once that gets installed you navigate to the directory where your game server app is located and type 'screen -S nameofscreen'
(where 'nameofscreen' is what you want to call the session)
Now execute the command to start the server, You will see the output of the server starting. Once this is going type ' ctrl+a+d to "detach" the screen.
Now you have a server running in the background and can log out as normal.
To go back later and "reattach" the session type ' screen -r nameofscreen'
Hope this helps.