private function getSingleOverview($overviewId)
    {
        // get specified overview
        $overviewRepository = $this->em->getRepository('KunstmaanDashboardBundle:AnalyticsOverview');
        $overview = $overviewRepository->find($overviewId);

        if (!$overview) {
            throw new \Exception('Unkown overview ID');
        }

        return $overview;
    }