Detour Novel re-issued basis of film

I have had a chance to read the original novel Detour written by Martin M. Goldsmith. The book was published in 1939 but was just re-issued a few months ago. Martin Goldsmith wrote the screenplay based upon his novel. A lot of the best dialogue in the film seems to have originated from the novel. It suggests that maybe Director Edgar Ulmer's role in creating this great film needs to be balanced with a bit more importance given to the role of the author of the original novel.