xbrli:precisionType 

This type is used to specify the value of the 
precision attribute on numeric items.  It consists 
of the union of nonNegativeInteger and "INF" (used 
to signify infinite precision or "exact value").

Simple Type Information

Used By

Attribute xbrli:numericItemAttrs/@precision

Source 

<simpleType name="precisionType">
  <annotation>
    <documentation>This type is used to specify the value of the precision attribute on numeric items. It consists of the union of nonNegativeInteger and "INF" (used to signify infinite precision or "exact value").</documentation>
  </annotation>
  <union memberTypes="nonNegativeInteger">
    <simpleType>
      <restriction base="string">
        <enumeration value="INF"/>
      </restriction>
    </simpleType>
  </union>
</simpleType>