CFA Institute has just published XBRL - A Guide for Investors. The title is pretty much self-explanatory. I'm glad to have contributed to it. Enjoy!
Also on the XBRL channel: Yesterday, L'Agefi published an article I've written. But when you follow the link, you'll see that it is written in excellent French, which cannot be me. Thanks for the contact and the translation goes to Marc Barbezat, member of XBRL CH!