title: Get context id corresponding to the current period
body: <p>I'm trying to parse a list of xbrl instance files. The filings (10-Q) correspond to different companies from different industries, reporting under us-gaap.</p>
  
  <p>I'm trying to extract the values of Revenue for the current 3-month period. In order to do that I'm trying to get the value of "us-gaap:Revenues" element.</p>
  
  <p>The problem is that there're many "us-gaap:Revenues" elements corresponding to different contexts. How do I let the parser know which context corresponds to the current period and is for the whole company (not for the segments)?</p>