from http://us.domain.org/detail.php?id=1234 to http://us.domain.org/category/city/computer-1234
Change your last rule to:
RewriteCond %{HTTP_HOST} !^www\. [NC]
RewriteCond %{HTTP_HOST} ^[^.]+\.domain\.org$ [NC]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^([^/]+)/([^/]+)/([^/-]+)-([^/]+)/?$ /detail.php?id=$4 [L,QSA]