Find and Replace Script for multiple files

I am trying to find a script that will either open a selection of .ai files or run through all the open files in illustrator and complete a Find and Replace. Right now I have a script that runs the Find and Replace but I have to run it on each document instead of all my open files.

var openDocument = app.documents.item(0); 
var search_string = /001D/gi; // g for global search, remove i to make a case sensitive search 
var replace_string = '001E';  
var text_frames = active_doc.textFrames;  
if (text_frames.length > 0) 
{     for (var i = 0 ; i < text_frames.length; i++)       {           var this_text_frame = text_frames[i];            var new_string = this_text_frame.contents.replace(search_string, replace_string);                        if (new_string != this_text_frame.contents)                {                     this_text_frame.contents = new_string;                }       } 
}

Thanks for any help.