function equalize() {
    if(document.getElementById('left_col') && document.getElementById('right_col')){
        var maxHeight = Math.max(document.getElementById('left_col').offsetHeight,document.getElementById('right_col').offsetHeight);
        document.getElementById('left_col').style.minHeight=maxHeight+'px';
        document.getElementById('right_col').style.minHeight=maxHeight+'px';
     }
  }

window.onload=equalize;