To detach the Alkaline process, you can either execute Alkaline with the & parameter, which is standard on Unix or with -d. The difference is that by running Alkaline with -d, it will not monitor the search thread pool and will not restart when an error occurs.
It is possible that you run Alkaline with & or -d and closing the terminal still kills it. This can happen on several Unix operating systems when the kernel does not support setpgrp()/setsid() and the SIGHUP signal cannot be caught by Alkaline. You can then try using the nohup utility.
The nohup utility invokes the named command with the arguments supplied. When the command is invoked, nohup arranges for the SIGHUP signal to be ignored by the process. Moreover, nohup will redirect output to a local file. Read man hohup for more details.
Under Windows NT, you should run Alkaline as a service in order to be able to logoff without stopping Alkaline or to automatically restart Alkaline when the server boots up. For more information, please read consult the Users Guide about running Alkaline as a Windows NT service.