Content is overheading the footer

Well, it’s not easy to explain, because my english is not very well.
The problem is that i’m working on my new website and I have a left sidebar, a middle content and a rightbar.

The problem is that not the sidebar, but the content and the rightbar, when the height’s getting larger than the sidebar it’s overheading the footer. The footer starts when the sidebar ends, but not when the content / rightbar ends. What to do?