No it wont, but there are ways you can cheat. One old trick is often called the "one true layout" trick. This works very well if you can get away with using hidden overflow on your parent container. In other words, if you need content (like drop menus) that extends outside the parent you can't use this trick.
What you do is set a very large bottom padding on the div you want to "stretch", and hide the excess by using an equally large negative margin. As an example:
.post_wrapper {overflow: hidden;}
.poster {padding-bottom: 5000px; margin-botom: -5000px; border-right: 1px solid #aaa;}