Hi Andrea,
If you simply want to make the Employee Details not load when you click on an Employee view box, you can set it so that detail is not used by the employee hierarchy (just click the 'trash' icon):
Otherwise, if you want to secure the Employee details panel by role, you can secure all tabs and sections in the configuration. Example:
There may be more sections than in my screenshot above which need to be secured, but these are the main ones. Obviously, you would need to add these secured items back to the roles which 'should' be able to see them.
The result will be that all roles which do not have the secured items added back will see a blank details panel when they load the employee details panel from anywhere in the application (not just from the org chart). I know you would prefer to hide the details panel completely, but a blank details panel is better than users seeing information they should not.
Best of luck.
Matthew