What is the recommended level of detail for published mathematical proofs?
What is obvious to you may not be obvious to others.
Let me repeat a story I told in another answer here. I'll just repeat it, but also note that user Stella Biderman commented that the story may be apocryphal and not from KU at all.

Here is a story (real occurrence) from the University of Kansas about 50 or so years ago. A prof, quite well known and respected, was lecturing in Topology. This meant writing proofs on the board. Occasionally a step wouldn't be filled in with the statement &quot;Of course it follows, trivially, that ...&quot;. On one such statement, a student didn't see the obvious connection and so asked. The prof looked at the board and the developing proof for a few minutes. Then walked over to the corner of the (chalk) board and started making notes to himself in a tiny script. He went into totally abstract thinking mode, ignoring the class. After a bit of writing and erasing, etc, he wandered out of the room toward his office. The students followed along, gathering outside the office. The prof started pulling books off of his shelf and consulting them - several books - several more minutes.
Then he seemed to find enlightenment and returned to the classroom. When everyone was again seated he announced. &quot;Yes, of course. It's trivial.&quot;

The conclusion is that you should make the connections yourself, and not rely on reviewers grokking it. If they don't make the connection they will comment on it and at least slow down acceptance. It is also possible, as the story above, indicates that you might actually be making too big a step or even an incorrect one.