Anything thoroughgoing is comprehensive — it pays extremely careful attention to details. Your thoroughgoing research most likely involved endless hours of sifting through multiple sources.
A thoroughgoing paint job will be neatly edged and precisely done, and a thoroughgoing government reform will involve a huge, involved overhaul of the system. This adjective has an old-fashioned sound these days, when thorough usually works just as well. Both words come from the Old English þuruh, "from end to end and side to side."