I would suggest asking engineers to document information they were seeking, when they receive it, in Confluence(under a reserved space). In that way most commonly requested information gets stored and engineers get into a habit of adding it in, in case the information is not present. Not all 250 engineers might participate at first, but when people start noticing the usefulness of this knowledge trove, they might chip in.
You would need to have a few volunteers to act as maintainers who should check regularly for the quality of the information that is being added, organize into relevant subtrees and create/update guidelines for adding new information.
This would also aid engineers who contribute improve their documentation skills as writing code is easier than writing about it IMHO.