difficult filter/sort

I have attached a file showing several fields with the headings starting at row1 column 1.
I would like to filter out the rows of data where the IDNumber has no blanks below them.

This is because I want to show rows wher there is an IDNumber and the blanks below because they are the IDs of people who have worked for different departments.

The original spreadsheets may have a copule of thousand rows in them.

Thanks very much for your help in this