Pascal GPUs run up to 83 degrees before throttling down to prevent overheating. The hard physical limit will be higher than that, since this is a firmware safety measure.
It's warm, but nothing to be alarmed of. High idle could be that the fans don't start to spin until a certain temp is reached, done for quiet light operation. If you want to make sure, run a stress test like MSI Kombustor or Furmark for a bit and see what temps you get.
You can improve airflow inside the case for better temps. Good rear exhaust helps a lot, good intake a little bit. To see if you need more airflow, open the side panel while running game or stress test. If temps improve more than 2 degrees consistently, there's a reason for improving airflow. Good case airflow shouldn't improve from opening side panel more than 2 degrees, and may even have worse temps with side open.