I created a video, How XBRL Works, which seems to be pretty popular for people who want to understand how XBRL works. (The video has over 50,000 views; about 463 views per month.)
But while I explain how it works, you don't actually get your hands dirty and use XBRL, seeing for yourself how it actually works.
Well, here is something else that helps you understand how XBRL works using Excel. The link is to a ZIP archive which contains an Excel spreadsheet. The spreadsheet has some very straight forward macros. What the macros do is extract information from the XBRL-based 10-Ks of 464 public companies that use interest-based revenues to report their financial information (i.e. banks).
To run the VBA code in the spreadsheet, all you need to do is click the one button in the upper left hand corner of the spreadsheet. You do need to have Microsoft Internet Explorer installed on your computer, the VBA code uses the Microsoft XML parser to extract information from the XBRL-based reports.
There is a great deal one can learn from reverse-engineering the VBA code. Also, if you notice the results of the information extracted and you ask yourself, "Why do some financial reports contain errors and others do not contain errors," you can learn even more.
If you are a CPA that understands how to write Excel VBA and you want to learn more about XBRL contact me. I am always looking for people to collaborate with to create interesting software. Experimentation is a great way to get ready for the digital age of accounting, reporting, and auditing.