var idWithOver = Array();

function isOffAllThumbnails() {
	var i = 0;
	for (i=0; i<idWithOver.length; i++){
		if(idWithOver[i]) {
			isOffThumbnail(i);
		}
	}
}

function isOverThumbnail(id) {
	isOffAllThumbnails();
	
	document.getElementById('overThumbnail'+id).style.display='block';
	document.getElementById('thumbnail'+id).style.display='none';
	idWithOver[id] = true;
}

function isOffThumbnail(id) {
	document.getElementById('thumbnail'+id).style.display='block';
	document.getElementById('overThumbnail'+id).style.display='none';
	idWithOver[id] = false;
}