A Calculated Risk

A detailed investigation into the complexities and limitations of XBRL Calculations
by: Shawn Rush, CompSci Resources, LLC

Complexities and Limitations

Period Type

One of the more noticeable limitations of the calculation specification is its restriction on mixing concepts of different period types in a single calculation. This limitation becomes obvious in the inability to specify a calculation in the stockholder's equity statement. The general structure of an equity table shows the stockholder's equity at a given point in time (instant) followed by changes over the course of some period of time (duration) whether it be a year or a quarter followed by the new balance (instant).

Despite the calculation being obvious in the table, we are unable to model it using XBRL calculations.

Basic Accounting Equation

The basic accounting equation using XBRL concepts is as follows:

Assets = Liabilities + StockholdersEquity

Unfortunately, this simple equation cannot be modeled with XBRL calculations because of balance type restrictions. Given that "Assets" is a debit and "Liabilities" and "StockholdersEquity" are both credits, there is no way to write this equation in XBRL with the proper calculation weights. In the equation above, either "Assets" or both "Liabilities" and "StockholdersEquity" would have to have a negative sign. Neither scenario makes sense so this important calculation cannot be included in the calculation linkbase.

Dimensional Calculations

As mentioned before, calculations only apply to facts that share the same context. Hence, if two facts have different dimensions (and consequently different contexts), then they cannot be part of the same calculation.

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