Float my tumblr sidebar

sidebar.js

(function($) {
$(function() {
    var $sidebar = $('#sidebar');
    var $win = $(window);
    var origOffset = $sidebar.offset().top;
    $win.scroll(function() {
        var top = $win.scrollTop();
        var offset = $win.scrollTop() - $sidebar.offset().top;
        var overlap = $sidebar.height() - $win.height();

        if (offset > 0 && overlap <= 0) {
            $sidebar.addClass('floatTop');
        } else if (top < origOffset || overlap > 0) {
            $sidebar.removeClass('floatTop');
        }
    });
});
})(jQuery);