How to identify period end contexts in xbrl filings? - xbrl

Question

I am trying to find only the current period concepts and facts for the three main financial statements. The goal is to be able to iterate through filings of different companies in different periods.
Using Ebay 2017 10-k as an example.
For concepts that capture YoY change, like those in income statement and statement of cash flows, I can use context found in any of the dei tags, for example:
<dei:DocumentFiscalYearFocus contextRef="FD2017Q4YTD" id="Fact-2E3E1FD4D81352F693510AE035FDC862-wk-Fact-2E3E1FD4D81352F693510AE035FDC862">2017</dei:DocumentFiscalYearFocus>
dei:DocumentFiscalYearFocus tag is required, and its context "FD2017Q4YTD" is also found in all IS and SCF period end concepts, so that's easy.
However, balance sheet concepts use a different context:
<us-gaap:CashAndCashEquivalentsAtCarryingValue contextRef="FI2017Q4" decimals="-6" id="d15135667e874-wk-Fact-3E4A0A2B272B59DE9DAF004097ECF968" unitRef="usd">2120000000</us-gaap:CashAndCashEquivalentsAtCarryingValue>
Any idea how to identify the "FI2017Q4" context (or otherwise find current period balance sheet concepts)?

Answer 1

The XBRL document instance you are viewing contains one or more schemaRef elements, each of which loads an XBRL taxonomy, or data dictionary, for the XBRL instance. Somewhere, within that reference graph of files (and there could be several files), is the definition of each context. The definition will look something like this:
<context id="CONTEXT_ID_NAME">
<!-- ... child elements appear here ... -->
</context>
If you can find the <context> element with an attribute of id that matches the contextRef you're interested in, then you've found what you're looking for. In your case, you're looking in the related XBRL taxonomy files for something that says <context ID="FD2017Q4YTD"> and <context ID="FI2017Q4">.
The child elements of the <context> element describes the dates for the context. There are two types of XBRL contexts:
instant, which specifies a context with a single date
period, which specifies a context with a start date and an end date
The child elements of the <context> element will describe which type of context being described.
This work is all manually doable, but it might be best to use XBRL processing software, which will perform all of this work for you.

Answer 2

The value of the contextRef attribute is purely an identifier that references a context definition elsewhere in the document. Using the eBay example, you'll find this context definition:
<context id="FI2017Q4">
<entity>
<identifier scheme="http://www.sec.gov/CIK">0001065088</identifier>
</entity>
<period>
<instant>2017-12-31</instant>
</period>
</context>
The value in the "instant" element is what tells you what date facts associated with this context relate to.
In order to properly understand the XBRL facts, you need to fully understand the associated contexts. There may be other information, such as additional dimensions, defined here.
I'd strongly recommend working with an existing XBRL processor that will resolve the contextual information for you, such as the open source Arelle processor, or the API provided by XBRL US.
One possible approach to working with XBRL data is to use a processor that converts data to the newer xBRL-JSON format, which provides fact objects with all contextual information fully resolved.