Historicist: Venema didn't supply a label, but those who hold to this position are generally advocates of a subset of Postmillennialism. Francis Nigel Lee is one of the better known adherents.
Idealist: Again, no label is supplied, but in a general
sense I think one could find Amillennialists in that group to one degree or another, although an Amillennialist, such as myself, would say that there would be a definite person, event, thing that the prophecies foretell at the end, aka: the 'already but not yet' principle; various fulfillments take place as types which all point to the one true fulfillment.
You might do well to read Venema's book, The Promise of the Future
where he goes into depth analyzing each of the various 'systems' and then presents his view, which is Amillenialism.
I got the impression that this article is part of a series. IF that is true, then the next installment(s) should clarify in more detail these things.