"Having to explain every minute detail" is not explicit in the definition of the word, but it is the sort of behavior you might expect from someone who

>***[patronizes](http://dictionary.cambridge.org/dictionary/british/patronize)***: speak to or behave toward someone as if they are stupid or not important

other people.

That particular meaning works with the verb form (patronize) and adjective form (patronizing). *Patronizer* is out there, but it seems to get more use for denoting someone who engages in the more pleasant sort of patronizing (sponsoring, supporting, or bringing trade to). If you're willing to accept a phrase rather than a single word, you could describe someone as a "patronizing overexplainer."

If you're just looking for an adjective, another suitable word is

>***[haughty](http://www.merriam-webster.com/dictionary/haughty)***: having or showing the insulting attitude of people who think that they are better, smarter, or more important than other people

though its definition also lacks the specific detail of feeling the need to explain minutiae to others.

P.S. I included links for the questioner because *common* search engines apparently proved too difficult. Positioning the mouse cursor over the red letters in italics and left-clicking with the mouse will open the pages with the quoted definitions.