Not a good one that is targeted at non-professional investors. I agree, it's a good opportunity. The issue is that companies have a lot of latitude in how they use XBRL once you get outside of the totally standard financial metrics like revenue, gross profit, total liabilities, etc. And those are the metrics that are already largely available in services such as Yahoo Finance for free. What would be really valuable is taking company specific metrics such as unit volumes, orders, backlog, etc. And that requires a ton of work for each company and some knowledge of what the business does. Also, a lot of that data is not yet broken out into XBRL. For example, look how much data from THO (an RV manufacturer) is useful but not detailed in XBRL fields:

https://www.sec.gov/ix?doc=/Archives/edgar/data/730263/00007...

You can see which parts have XBRL tags by the red lines above and below. If you search the document for "orders" or "units" you can see lots of great information that is basically stranded. I've always thought that it shouldn't be that hard to use a bunch of heuristic rules to find data that is present in the last N 10-K or 10-Q filings (particularly because they tend to reference the previous year results, so you can search for numbers that are the same that are located within K words of certain strings).

But it's hard to do something really useful as a one-person effort with some clever coding, which is probably why the services that are out there are niche and expensive.