I've been researching this for hours now and it seems to be an IE thing but my issue is that I have a container DIV that, in IE9, doesn't expand and cuts everything off after about 400px. Chrome and FF work perfectly, of course.

Container DIV

#main_container{
font-family: arial, verdana;
width: 920px;
top: 0;
margin-left: auto;
margin-right: auto;
background-color: #fff;
overflow-x: hidden;
}

Page Container DIV

#page_container{
font-family: arial, verdana;
font-size: 14px;
width: 900px;
color: #000;
border: 0px solid;
overflow: hidden;
}

And the standard markup of page block looks like this

<div id="main_container">
  <div id="page_container">
    Variable page data goes here
  </div>
</div>

Is there an issue with my CSS that I'm missing or is there an IE hack that I need to apply?