Demand side here: The more details the better. It looks bad if the letter is less than 3-5 page long. We want to learn everything about you. In addition to your research and teaching statement we want to know: What motivates you? What are your views on the current world affairs? What do you like doing for fun? Do your interests outside school coincide with those of your future colleagues? What made you enter a graduate school?
I hope you find it useful and good luck with your market!!