This process has been going on since 1970. In 1970 the Senate introduced estimates hearings, but a lot of changes have happened to the process over that period. It's become much more elaborate.
The introduction of the supplementary hearings, for example, was one great change. The explanatory notes provided by departments have become more and more detailed and elaborate. The preparation that goes on before the estimates hearings has become much more intense and focused. The process on a superficial view remains the same. You have the hearings, and the estimates process is basically the same, but a much more intensive effort has gone into the process along the way.
The process of taking questions on notice by departments has greatly expanded. They take a lot of questions on notice, both before and during the hearings, and they present very detailed written answers in the course of the hearings and after the hearings. Senators complain that departments are not fast enough in getting their written answers in, but they are certainly very detailed when they present them.