function adjustLayout(){
	var xwidth = window.document.body.clientWidth;
	var mainntab = document.getElementById('main_table');	
	if( xwidth < 1200){
		mainntab.style.width = '100%';
	} else {
		mainntab.style.width = '80%';
	}
}

window.onload = function()
{
  xAddEventListener(window, "resize",
    adjustLayout, false);
  adjustLayout();
}