At about 09:05 eastern time, a Beech 200 lost its cabin door during cruise flight near Greeleyville. The pilot landed without further incident. The pilot said he was bound for Brunswick, Ga., to pick up passengers and was cruising at FL 200 in smooth air when the cabin door light illuminated and the aircraft lost pressurization. He went on oxygen and made an emergency descent. He looked towards the door and could see light from near the door area but did not know the door was separated until he landed at Savannah International Airport.