Hi,
Did you tried Brenden's example without using brackets at the end (without '()')? Should try something like this:
{% foreach (x in Documents[NodeAliasPath].Children.WithAllData){ %}
{%x.GetValue("ColumnName")%}
{% } |(identity)GlobalAdministrator%}
Which version of Kentico you are using? There was an issue with Documents macro in Kentico 10, which is fixed in hotfix 10.0.4 I think.
Best regards,
Dragoljub