$(document).ready(function(){
	detectBottom();
	$(window).resize(function() {
		detectBottom();
	});
});	


function detectBottom() {
	if ($(window).height()<$('#js_docsize').height()) {
		$('#js_placeholderbottom').replaceWith('<div id="js_placeholderbottom"><!-- placeholder for bottom image --></div>');
	} else {
		$('#js_placeholderbottom').replaceWith('<div id="js_placeholderbottom" class="js_bottombackground"><!-- bottom image div --></div>');
	}
}