Roy-
First, what size film will you be shooting? If you're shooting 35mm, then Tri-X is going to give you grain...sort of a "journalistic" look. That's not necessarily a bad thing depending on what you're trying to accomplish. This leads naturally to the 2nd question: What are you trying to make pictures of? You say that you want fine grain and lots of detail, but you might get different recommendations if you want these things for pictures of flowers versus pictures of buildings or landscapes.
In easily available film today, you can go with exotic films like Gigabit and get some amazingly small grain, or you can go for TMax-100 for one of the finest grained films that you can buy anywhere that you can buy black and white film. (A lot of us never found love for TMax-100, but it is definitely fine grained.) Personally I don't shoot either of those films...when I want the ultimate in sharp, detailed images, I shoot Fuji Acros and develop it in Rodinal 1+100. But that's my choice, for my subjects, using my equipment. Knowing what your subjects are and what size film you're shooting will help us give you a better recommendation.
If you're shooting 4x5 or 8x10, then you don't really have to worry about grain. I shoot Efke 100 and J&C 100 Pro in those sizes; not the finest grained films available by a long shot but you'd never know that from my prints. Since the enlargement factor is so small, any film will look fine grained. In medium format I shoot mostly Efke 100, J&C 100, and Fomapan 200...again, not the finest grained films, but they work for me.
But when I want fine grain, I turn to Acros. It's a wonderful film, and the tonality it provides matches what I want, so it's what I use. Is it as fine-grained as TMax-100? Honestly, I don't know. I do know that I've shot both films in 35mm and 120, and I liked the Acros more. Plenty of people must like TMax-100 because Kodak sells a lot of it...I happen not to be one of them. But this is a matter of taste...the tonalities and color response of Acros match my personal vision more than TMax-100. Knowing what you're taking pictures of and what size film you're using will help us help you...some of us will probably even recommend TMax-100!
Best of luck to you.
Dave