Sidebars not displaying right

Ok so i bought a theme a little while ago for a site of mine, but now i am modifying it to work with a new site i am making. I have my main content (located in the center) with two sidebars on both sides of it. I currently have this in my CSS

.content {
float: left;
width: 615px;
padding: 10px 0px 0px 10px;

}
#sidebar_right {
float: right;
background: #DDD;
padding: 0 5px;
width: 170px;
border-left: 1px solid #777;
}
#sidebar_left {
float: left;
background: #DDD;
margin: 0px;
padding: 0 5px;
width: 170px;
border-right: 1px solid #777;
}

And this is what the output looks like:

https://www.fuckedupideas.com/test.jpg

What my problem is, is that i want the side panels to go all the way down to the bottom of the page ( equal length as the longest panel ). I know that i have seen other themes that just have a jpg image of the entire width of the screen ( 1000px ) that has the image of the left sidebar / main content / right sidebar, but i am trying to do this a different way.

Any Ideas??