Basically in your custom subscribed service,you have to loop on /IDOC and map (one to one of each each segment/fields including EDI_DC) to a temp document called (extract_singleIDOC) and publish it at that moment and drop the temp and it continue next iterations which will perform same above steps and once all iterations done it will end the loop.So make sure you have all the individual publishes happened.
Sorry If I misunderstood your question above:
HTH,
RMG
#webMethods#edi#Integration-Server-and-ESB