A document feeding device is described for generating a singulated flow of documents, such as mail pieces from a stack of documents. The documents may then be sorted to destination storage areas based upon the address information which each document bears. The present device is especially useful in processing mail flats. The double feeding of documents is substantially prevented by the device which effects the continued separation of the documents in a plurality of stages while they are all in a dynamic state. More specifically the device utilizes a buffer technique wherein simultaneous separation can take place in two series stages on different documents during the singulation process.