try this css:
#dialog {
overflow : visible;
}
.ui-dialog {
overflow : visible;
}
-- EDIT
Sari Alalem is right this will affect other dialog. The solution that I can think of without affecting other dialog is basically by adding another class with overflow:visible or changing css property of the parent of #dialog (after rendering dialog) using JavaScript:
With other dialog in mind, the solution should be
#dialog {
overflow : visible;
}
$('#dialog').dialog().parent().css('overflow', 'visible');