As you have guessed, the process hlds is attached to your session. As you close your session, you end all your processes including your hlds server. You can use screen for that. Try this :
screen -A -m -d -S hlds ./hlds_run -game cstrike +maxplayers 20 +map de_aztec
or screen -A -m -d -S ./your_start_script.sh
Then to get to your server type :
screen -r hlds
and if you want to reconnect from yet another terminal, type :
screen -D -r hlds
which will disconnect the old session and reconnect to yours...
You will see your server in your terminal window.
Get all the info from :