window.onload = TakeWholeHeight;
window.onresize = TakeWholeHeight;

function TakeWholeHeight(ev) {
	var clientHeight = document.documentElement.clientHeight;

	var targetElement = document.getElementById('divMainContent');

    var minHeight = clientHeight - targetElement.getBoundingClientRect().top - 25;

    var newHeight = targetElement.offsetHeight;
	if (newHeight < minHeight)
		newHeight = minHeight;
       
    targetElement.style.height = newHeight + 'px';
}