function Fensterhoehe(win) {
	if (win == undefined) win = window;
	if (win.innerHeight) { return win.innerHeight; }
	else {
		if ( win.document.documentElement && win.document.documentElement.clientHeight ) {
			return win.document.documentElement.clientHeight;
		}
		return win.document.body.offsetHeight;
	}
}

function contentresize() {
	var windowHeight = Fensterhoehe();
	var imagePart1 = document.getElementById("main_headline").offsetHeight;
	var imagePart2 = document.getElementById("main_navi").offsetHeight;
	var imagePart3 = document.getElementById("main_content").offsetHeight;
	var imagePart4 = document.getElementById("main_bottom").offsetHeight;
	var totalHeight = imagePart1 + imagePart2 + imagePart3 + imagePart4;
	if (totalHeight < windowHeight) {
		var newcontentHeight = imagePart3 + (windowHeight - totalHeight) + 8;
		document.getElementById("main_content").style.height = newcontentHeight + 'px';
	}
}