function fixHH(one,two) {
	if (document.getElementById(one) && document.getElementById(two)) {
		var oneHeight = document.getElementById(one).offsetHeight;
		var twoHeight = document.getElementById(two).offsetHeight;
		
		var newHeight = Math.max(oneHeight, twoHeight);
		
		document.getElementById(one).style.height = newHeight + "px";
		document.getElementById(two).style.height = newHeight + "px";
	}
}

window.onload = function(){ 
	fixHH('zijbalk','content');
}