function getWindowHeight() {
	var windowHeight = 0;
	if (typeof(window.innerHeight) == 'number') {
		windowHeight = window.innerHeight;
	}
	else {
		if (document.documentElement && document.documentElement.clientHeight) {
			windowHeight = document.documentElement.clientHeight;
		}
		else {
			if (document.body && document.body.clientHeight) {
				windowHeight = document.body.clientHeight;
			}
		}
	}
	return windowHeight;
}

function setFooter() {
	if (document.getElementById) {
		var windowHeight = getWindowHeight();
		if (windowHeight > 0) {
			var headHeight = document.getElementById('kopf').offsetHeight;
			var middleHeight = document.getElementById('mitte').offsetHeight;
			var headElement = document.getElementById('kopf');
			var logoElement = document.getElementById('logo');
			var menuElement = document.getElementById('menu');
			var middleElement = document.getElementById('mitte');
			var footerElement = document.getElementById('fuss');
			var footerHeight  = footerElement.offsetHeight;
			if (windowHeight - (headHeight + middleHeight + footerHeight) >= 0) {
				footerElement.style.position = 'absolute';
				footerElement.style.top = (windowHeight - footerHeight) + 'px';
				footerElement.style.visibility = 'visible';
			}
			else {
				footerElement.style.position = 'absolute';
				footerElement.style.top = (headHeight + middleHeight) + 'px';
				footerElement.style.visibility = 'visible';
			}
		}
	}
}

window.onload = setFooter;

window.onresize = setFooter;