function getWindowHeight() {
  var windowHeight = 0;
  if (typeof(window.innerHeight) == 'number') {
    windowHeight = window.innerHeight;
  }
  else {
    if (document.documentElement && document.documentElement.clientHeight) {
      windowHeight = document.documentElement.clientHeight;
    }
    else {
      if (document.body && document.body.clientHeight) {
        windowHeight = document.body.clientHeight;
      }
    }
  }
  return windowHeight;
}
function setContentHeight() {
  if (document.getElementById) {
    var windowHeight = getWindowHeight();
    if (windowHeight > 0) {
      var mainHeight = document.getElementById('main').offsetHeight;
      var footerHeight = document.getElementById('footer').offsetHeight;
      var contentElement = document.getElementById('content');
      if (windowHeight - (mainHeight + footerHeight) >= 0) {
        contentElement.style.height = (windowHeight - footerHeight) + 'px';
      }
    }
  }
}
window.onload = function() {
  setContentHeight();
}
window.onresize = function() {
  setContentHeight();
}