xbrl us gaap contextRef standard?

Please tell me this is standardized, or at least there is some way to decipher it.

I'm looking at these 3 random 10-Qs and Ks from 2012Q4.

The line items are standardized; however, there are many of them per document. For instance, one document will have a few us-gaap:OperatingIncomeLosses, and the only way I can tell that they denote which period they are reporting is with contextRef. That's where things get complicated.

I see no discernible pattern. Sometimes they're ascending then descending. They all have their own date formats. Some do multi-period grouping. Some don't.

I've tried to find a standard on this. No go.

Does anyone have any ideas?

Many thanks!

Solution

its in xbrl 2.1 specification
http://www.xbrl.org/Specification/XBRL-RECOMMENDATION-2003-12-31+Corrected-Errata-2005-04-25.htm#_4.6.1

      <context id="BalanceAsOf_20120531">
        <entity>
          <identifier scheme="http://www.sec.gov/CIK">0000866729</identifier>
        </entity>
        <period>
          <instant>2012-05-31</instant>
        </period>
      </context>
      <context id="BalanceAsOf_20120531_AccumulatedOtherComprehensiveIncomeMember">
        <entity>
          <identifier scheme="http://www.sec.gov/CIK">0000866729</identifier>
          <segment>
            <xbrldi:explicitMember dimension="us-gaap:StatementEquityComponentsAxis">us-gaap:AccumulatedOtherComprehensiveIncomeMember</xbrldi:explicitMember>
          </segment>
        </entity>
        <period>
          <instant>2012-05-31</instant>
        </period>
      </context>
      <unit id="USD">
        <measure>iso4217:USD</measure>
      </unit>
    <us-gaap:AssetsCurrent contextRef="BalanceAsOf_20120531" unitRef="USD" decimals="-5">929900000.0</us-gaap:AssetsCurrent>
    <us-gaap:Assets contextRef="BalanceAsOf_20120531" unitRef="USD" decimals="-5">1670300000.0</us-gaap:Assets>
    <us-gaap:StockholdersEquity contextRef="BalanceAsOf_20120531_AccumulatedOtherComprehensiveIncomeMember" unitRef="USD" decimals="-5">-74200000.0</us-gaap:StockholdersEquity>

for example; consider these two context; ids needs to be unique with respect to their content(With respect to period entity; and entity with its sub elements; identifier and segment if present)
we will use its id to map financial facts. Here in example AssetsCurrent refers to unit--> whose id is USD and context information--> whose id is BalanceAsOf_20120531; and detail of this this context id can be found in context element. here everything should be unique other wise it will create duplicate facts/contexts. You can see here that; both context has same period but so why can't their ids? because one context has addition detail segment information.
(i am not going in detail here; if you want to know; how it is detecting duplicate/error consider example no 25 and 26 from the link.)
in other way you can also view facts/values with three axis as CIK period and xmlname;and this uniqueness makes them comparing with other company's facts with these axis.