Within iXBRL reporting (for
ESEF), the html report that is created, is ultimately based on the annual report that is created in Disclosure Management. This is a Word document, and therefore can use (non-standard) fonts.
This blog will show how to get these embedded in the iXBRL html report
1 . In the Word chapter, user is using various font

Note: one of these (Blender Pro) is a non-standard font

2. The iXBRL report is generated

3. The Task Engine server that was used

4. Server where Task Engine runs
This server has the font installed.

IMPORTANT: it is not the Disclosure Management application server that creates the instance. It is the machine that runs the Task Engine.
This can be the same server, but this is not always the case. Also be aware that if you have multiple Task Engine servers, that the font(s) need to be installed on all servers
Note: if the font is not installed, some substitute font is used (e.g. Arial, Calibri) - the system has no control over which fonts are used in the replacement
5. Result

6. Verify the instance
To really check this, you can open the instance file with
Notepad++
In the file, you will see that the fonts are embedded in the
<style type="text/css">

One final remark, the use of these fonts can significantly increase the size of the html report (and also the previewer file), so check with your local regulator if there is any limitation on file-size that can be submitted.