Extend author_info

So, I wanted to change the background of the author_info and for some reason it doesn't seem to extend to the bottom of the post_body. I've tried making the height 100% and inherit still nothing.

Here is what I'm seeing.

CSS:

.author_info {
        width: 155px;
        float: left;
        background: #F8F8F8;
        min-height: 100%;
        font-size: 12px;
        text-align: center;
        padding: 15px 10px;
}