I have an idea for what I think would be a great documentary. The format could be used as a book also, and I think it would be successful. If you were in the same position, what what you do first, the book or the film?
I think this is a common misconception based on a series of high-profile cases. I actually think that when you look at the number of movies that are adapted from half decent books then you'll see that the ratio is pretty even.
Remember that Stand by Me, The Shining, Shawshank Redemption...etc are all adapted from stories by Stephen King.
How many people would read your book?