idealists just instantly giving up when it comes to knowing reality thru materia, they only care about thinking and theoretising
dealictical materialists still admit that reality is unknowable (so they are still idealists in the core) but they say we can use matter and senses to get at least somthing
this is how i understand it, materialism - matter first, consciousness later; idealism - consciousness first, matter later. But i dont think this is right to talk about idealism as a whole, firstly we need to choose one and then discuss