A terminal is automatically going to be suspended after 2 hours of idle time by default. We use dev/pts to find the idle time, which is the same as the IDLE column in w command's output. If you want to change the time, create .waza_suspend file in the home directory and put an integer value in it.
For example, below you can see 150. The terminal is going to be suspended after 150 minutes if it has been idle for 150 minutes.
shohey1226@r34:~$ cat ~/.waza_suspend 150
In case you don't want to suspend your terminal, like a background job that runs a long time, put 0.
shohey1226@r34:~$ cat ~/.waza_suspend 0