Diaries in Nazi Germany

I've been reading The Rise and Fall of the Third Reich and it seems like nearly every influential figure short of Hitler himself kept a detailed diary. Is this situation normal for the time, both within and outside of Germany? Did the average person at this time keep a diary, or was it just those in politics or positions of power? Are these detailed diaries an aberration of history or do we see a lot of instances were primary figures kept personal records like this?