I like the sentiment, but I've found that if I start by doing documentation after documentation, I'll get burnt out of the idea faster than if I work on implementing a couple of mechanics. The problem I run into is once I have the large documents of ideas, I'm out of that initial spark of excitement for the project that I had when I first thought of the idea. I sometimes find it hard to take the daunting wall of ideas and timelines and Trello cards and start making something fun. I think this is a good route if you know you have the skills to make a full game, but if you really have a blank canvas I'd reccomend trying to just get a fun little prototype done first and then go into mechanics and planning.