URL masking using mod_rewrite

I am trying to redirect one URL to another, except that I want the original URL to remain in the browser address window.

Entered URL:  http://www.website.com/news/2011/03/24/energy-saving-beyond-the-earth-hour/19639

Destination URL:  http://www.website.com/news_detail.php?pr_id=19639

(The number following the final slash in the entered URL matches the ID in the destination URL)

What I have below is redirecting properly, but the destination URL is showing up instead of being masked as what was originally entered.  How can I fix this so that the URL that was entered remains in the address window?

Options +FollowSymLinks
RewriteEngine On
RewriteBase /
RewriteRule ^news/([^/]+)/([^/]+)/([^/]+)/([^/]+)/([^/]+)$ http://www.website.com/news_detail.php?pr_id=$5  [NC,L]