A Calculated Risk

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

Introduction

Few individuals in the eXtensible Business Reporting Language (XBRL) community would disagree that calculations are one of the more confusing and frustrating aspects of the specification. In theory, calculations should be fairly straightforward. All the numbers on the financial statements should add up to the stated totals, but as we know the devil is in the details. Hopefully we can shed some light on those details by reviewing not only the basics of creating calculations, but also certain scenarios that are either tricky or downright impossible given the current limitations of the specification.


Basics

We'll start with the basics of how XBRL calculations work. Let's say we have the following on our balance sheet:


In our calculation linkbase, the XML tags for this calculation would look something like this:

   <calculationArc
        xlink:type="arc"
        weight="1"
        order="1"
        xlink:to="us-gaap_Liabilities"
        xlink:from="us-gaap_LiabilitiesAndStockholdersEquity"
        xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item"/>

   <calculationArc
        xlink:type="arc"
        weight="1"
        order="2"
        xlink:to="us-gaap_StockholdersEquity"
        xlink:from="us-gaap_LiabilitiesAndStockholdersEquity"
        xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item"/>


Note that "xlink:to" denotes the operand whereas "xlink:from" denotes the total. The other important item to look at is the "weight" value. While the XBRL specification allows any numeric here, the U.S. Securities and Exchange Commission (SEC) only allows values of either [1] or [-1]. Weight determines whether we are adding or subtracting the operand. Hence, the above XBRL is expressed in a human-readable format by the following equation:

Liabilities + StockholdersEquity = LiabilitiesAndStockholdersEquity




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