The closest thing I can find to a published script API is the InDesign Scripting Guide pdf (by the way Adobe, I know you love pdfs, but it is an awful format for documentation, these sort of documents is actually what HTML was invented for - use it pretty please?)
However, this only seems to discuss the api that is available from within InDesign. I am scripting InDesign server and it seems to be somewhat different, for example activeDocument is not actually a property on app. Is this API actually published anywhere?