Modern automobiles has a computer controlled temp gauge. It goes to the middle...and stays there. In actual fact the car's temperature varies quite a bit, but the automakers don't want people to worry as long as the temperature is within a nominal range. So the needle don't move much.
Your gauge is giving you an accurate reading, showing the temperature fluctuations that really occur. And yes, expect a temperature rise at idle. As long as the fan is kicking in and controlling the temperature properly, you're OK.
