I was wondering if there's an idiom or expression for a person who knows everything there is to know about their field of interest or expertise, practically no detail is unknown to them.
I thought of the expression: knowing something like the back of hand, but I guess that has a geographical sense to it and is used for cities, streets, or neighbourhoods. (Please correct me if I'm mistaken.)
In this situation, I would say he "knows it backwards". The implication is that one knows something so thoroughly that they could do it in reverse.
Also consider
"knows it backwards and forwards"
{Cambridge Dictionary of American Idioms}
and "knows it inside out"
{McGraw-Hill Dictionary of American Idioms and Phrasal Verbs}.
"knows it like the back of his hand" does often, but not always, have a geographical connotation.
That sounds like a "subject-matter expert (SME)."
A subject-matter expert (SME) or domain expert is a person who is an authority in a particular area or topic.
One idiom that people in the United States sometimes use to describe a person who possesses extensive, detailed knowledge of a particular subject is walking encyclopedia. Here is the entry for that term in Christine Amer, The American Heritage Dictionary of Idioms (1997):
walking encyclopedia A very knowledgeable person, as in Ask Ron—he's a walking encyclopedia of military history. A similar expression, a walking dictionary, was used by George Chapman in his poem "Tears of Peace" (c. 1600)
To know something like the back of one's hand.
To be intimately knowledgeable about something
'This professor is extremely knowledgeable, he knew Physics like the back of his hand.'
Given your example sentence, nuts and bolts is an idiom you could use.
Nuts and bolts: The basic practical details
Here are some examples of usage from Oxford Dictionaries Online:
The nuts and bolts of making a movie...
He tends to hire ambitious people who have their eye on a startup and a knack for the nuts and bolts of practice.
Personally I think that has an intimate (or encyclopædic) knowledge of [field] is idiomatic per se.
Consider every jot and tittle
Every minor detail. A jot is the horizontal mark on the letter "t", and a tittle is the dot above an "i" or a "j".
Urban Dictionary
Also from soup to nuts
Also, from A to Z or start to finish or stem to stern . From beginning to end, throughout, as in We went through the whole agenda, from soup to nuts, or She had to learn a whole new system from A to Z, or It rained from start to finish, or We did over the whole house from stem to stern. The first expression, with its analogy to the first and last courses of a meal, appeared in slightly different forms (such as from potage to cheese) from the 1500s on; the precise wording here dates only from the mid-1900s. The second expression alludes to the first and last letters of the Roman alphabet; see also alpha and omega. The third comes from racing and alludes to the entire course of the race; it dates from the mid-1800s. The last variant is nautical, alluding to the front or stem, and rear or stern, of a vessel.
As noted, also from A to Z, from start to finish and from stem to stern.
American Hertiage Dictionary of Idioms at thefreedictionary.com
