XBRL: Connecting a fact to presentation via context

Question

As best I can tell, XBRL allows SEC filers to use the same concept for multiple facts so long as the context is different. I'm having a difficult time understanding how to include/exclude a fact for a given roleURI (a statement, for instance). I believe this ability is somehow related to context, but there doesn't seem to be an obvious link between the concepts asked for in the presentation document and the appropriate concept in the instance. To ask this a different way:

1) The company has several roleURIs (networks), perhaps one of which is "http://www.bigcompany.com/role/StatementOfIncome"

2) In the *_pre.xml document section related to this network, the company has asked that a "Revenues" concept be displayed.

3) The instance document has multiple "revenue" items, each with different contexts, and some with segments related to the company's sub-entities.

How do I determine that a revenue item with a certain context belongs on the StatementOfIncome roleURI, and another one should be excluded?

Thanks for any hints or resources...

Answer 1

As you note, the presentation linkbase is context-agnostic. From the exhibits themselves, there is no explicit way to know which numbers were actually printed on the Income Statement and which facts using the same element/concept are from other schedules.

The SEC uses programmatic means to determine what will be rendered where in its Pre-Viewer and Viewer; they explain some of that in their FAQs and Interpretations (see, for example, question B.3 at http://www.sec.gov/spotlight/xbrl/staff-interps.shtml). They look at key words and phrases.

The SEC makes the source code to their rendering engine available at http://www.sec.gov/spotlight/xbrl/viewers.shtml - you may be able to leverage it or find other hints of how they determine what to print and when.

XBRL was not designed to recreate the original presentation; later developments including Inline XBRL and the new Table Linkbase do more to preserve presentation placement.

Answer 2

I accepted the given answer as correct, but after several more days of banging my head on this issue, I can't quite yet see it. I keep thinking that facts somehow HAVE to "belong" to a network via their context. As best I can tell, facts with contexts having segments belong on networks with hypercube dimensions that match (somehow) the context segment "explicitMember" values. Facts with context without segments belong on networks either that have no hypercube dimensions or that relate to the company has a whole. But I can't make heads or tails of this. When I've gone through and looked at how XBRL gets made using software, facts and contexts are added to documents as networks are added. Somehow, there's a connection there. The SEC's software is helpful, but I haven't quite wrapped my head around what they did either.

I wish there were better resources on learning to parse XBRL. Most of what I've seen relates to creating it...

If ever I figure this out, I'll revisit this question with better details!