Is it a good idea to write a larger than expected project report? A professor expects a report for a project to be around 3-4 pages (but never said anything, this is only my guess).

Is it a bad idea to submit a report of 12-13 pages if it contains useful information and detailed analysis? Doesn't this show I am interested in the subject?
If I say "3 or 4 pages" and get 5, not problem. If I get 12, my first reaction is to give minimal grade, for not following simple guidelines. If I'm in good mood, I'd read it (unlikely, term's end isn't a time for jollyness ;-), and if it really dazzles me (no rambling, no unending tables that could have been summarized in a graph or two, does the work asked, and goes far beyond it in useful direction) I might even give some extra credit (and bookmark you for later). If just longwinded explanation that could be summarized in 3 pages, again fail.