jQuery(document).ready(function($){
    var $sidebar = $('.sidebar:eq(0)');
    var sidebarPos = false;
    function resizeScreen() {
        if ( $sidebar.length ) {
            sidebarPos = {
                top:$sidebar.offset().top - 60,
                bottom:$sidebar.offset().top + $sidebar.find('.sidebar-content').height() - $(window).height() + 20,
                width:$sidebar.width(),
                footer:$('#footer').offset().top - $(window).height(),
            }
            $('.sidebar-content').css('width',$sidebar.width());
        }
    }
    $(window).on('resize',resizeScreen);
    resizeScreen();

    var scrollPos;
    function scrollScreen() {
        if ( sidebarPos ) {
            scrollPos = $(window).scrollTop();
            if ( scrollPos > sidebarPos.top ) {
                $sidebar.addClass('fixed-for-top');
                if ( scrollPos > sidebarPos.bottom ) {
                    $sidebar.addClass('fixed-for-bottom');
                    if ( scrollPos > sidebarPos.footer ) {
                        $sidebar.addClass('fixed-on-footer');
                    } else {
                        $sidebar.removeClass('fixed-on-footer');
                    }
                } else {
                    $sidebar.removeClass('fixed-for-bottom');
                }
            } else {
                $sidebar.removeClass('fixed-for-top');
            }
        }
    }
    $(window).on('scroll', scrollScreen);
    scrollScreen();
});

.sidebar{
  position:relative;
}
.sidebar.fixed-for-bottom .sidebar-content {
    position: fixed;
    bottom: 0;
}
.sidebar.fixed-on-footer .sidebar-content{
    position:absolute;
}