Unique document number independent of document type.

We are working on a cross business SAP PLM project and I have a question regarding document numbering. We want to have two different methods for numbering. Automatic and manual (you might call it internal and external). Is it possible, in SAP, to have a unique document number independeny of document type? For example, if internal/automatic document number 123456 is assigned to a new DIR, with document type ABC, we want that number to be comsumed, and not available to be used to create any other document type. Is this not possible? We do not want to have the document type be part of the DIR number, nor do we want to have to sustain different document number ranges for each document type.

Thanks for your help,

Joseph