Some suggestions to improve this:
- Split the navigation panel in two panels with seperate vertical scroll-bars as soon as the number of open documents exceeds a certain treshold
- Add levels for detail-documents beneath open documents and collaps them the same as the menu tree with (automatic) collapsing and expanding
- Add context (part of the breadcrumb) to the title or mouse-over of detail-documents to prevent having to open a document to see wich one is the right one
- An option to lock an open document, so that it is available the next time I login to the application