All XBRL numeric facts must be tagged with a unit of measure. This article supplements the EDGAR Filer Manual guidance on what must be reported as an XBRL numeric fact, and the relationship between a concept’s item type and its unit of measure.
One of XBRL’s primary purposes is to provide a machine readable representation of your financial report that is faithful to the meaning of the original value. Tagging numeric facts with units and utilizing ISO 8601 formats for time period values eliminates ambiguity when your XBRL documents are interpreted by software applications.
Numeric Facts and Time Periods
All numeric values in the required disclosure sections of your report must be tagged as XBRL facts. This includes numeric values that are somewhat hidden in text, concept names, or labels.
For example, the label Senior Secured Note Due 2016 at 6.125% [Member]. Placing a debt’s interest rate within the name of an identifying [Member] item is a common way to distinguish one debt instrument from another. This is an acceptable naming convention. However, you must still detail-tag the stated interest rate as a numeric fact.
Another common practice is to report quantities of a commodity; for example, "2000 barrels of oil." You must record this quantity (2000) as a numeric fact, along with a unit that represents the commodity for a barrel of oil (bbl).
Facts that describe a specific and known duration of time should be tagged with an element using the duration item type. For example, the fact "one year" must appear in the form as P1Y to follow the ISO 8601 standards. ISO 8601 is the international standard for representing dates, times, durations and periods issued by the International Standards Organization.
A further requirement is to report each numeric fact value with a unit that is consistent with the item type of the fact’s XBRL concept. Here are some tips to expand on this requirement:
All XBRL concepts are defined to represent a particular item type or data type. An item type can be something like monetary, area, time, energy, etc.
All XBRL numeric facts are assigned a unit of measure. For example, a fact value of 149 with USD as the unit of measure communicates $149.
Each item type can be assigned only a subset of all possible units of measure. In other words, the item type determines which units you can use.
Commonly Used Units
When deciding on a unit, you must take into account the item type of the concept, and then use or create an appropriate unit. The units of measure for each item type can be found at this link on the XBRL.org website under “Commonly Used Units.”
If you select one of these standard units in Wdesk, the utreg: prefix is added automatically, meaning that this value is defined in the XBRL Units Registry. If you create custom units, Wdesk inserts your company’s XBRL Namespace Prefix. This item is set at the account level by your Wdesk account administrator.
Additional information can be found in question E.21 of the Staff Interpretations and FAQs Related to Interactive Data Disclosure.