Issued: April 27, 2012
Impact: All US GAAP


The SEC Previewer does not currently support rendering of period facts reported using the ISO8601 weeks format.  Is the use of this format permitted in SEC filings?

Per the official specification for ISO8601, as of 2004, the format of PnnW is included to allow the specification of a period in number of weeks.  This is unique in that the “W” indicator cannot be combined with the other period indicators supported in the format PnnYnnMnnDTnnHnnMnnS.

However, the current XBRL specification refers to an earlier version of the XML standard that does not include support for weeks.  As a result, no implementation of XBRL supports the use of weeks in a filing using PnnW. If a filer expresses duration in weeks, the week’s duration format cannot be used.

Two methods have been used to deal with this situation

  1. Create a durationStringItemType as an extension and use the week format.
  2. Use the durationItemType and convert the weeks to days by multiplying by 7.


The filer should use the durationItemtype concept defined in the taxonomy or create an extension durationItemType where no concept exists in the taxonomy.  The filer should convert weeks to days by multiplying the value by 7 and reporting the durational period in days.  The filer also has the option to convert the weeks to other periods such as months and days.