The SEC maintains a site that answers several questions regarding XBRL.  It is located at http://www.sec.gov/spotlight/xbrl/staff-interps.shtml.

Among the many items listed, we thought it important to highlight the following items pertaining to zero- or nil-values:

Question 9

Q: How do I arrange for facts with different types to appear on the same row?

A: None of the Commission viewers can currently render facts of different types on the same row.

Question 10

Q: How do I force a row that is entirely nil-valued facts to render?

A: The current version of the Interactive Data viewer will not render a row of entirely nil-valued facts.

Question 36

Q: Should elements for line items appearing with a "-" in the original HTML/ASCII version be tagged with a "0"?

A: No. These items should not be tagged, which will render a blank field by the rendering engine. Tag an element with a "0" value if and only if the fact appears as a "0" in the original HTML/ASCII version.

Question 39

Q: For empty cells in a table appearing in the original HTML/ASCII version, should a filer tag those facts with a "0"?

A: No. These items should not be tagged, which will render a blank field by the rendering engine. Tag an element with a "0" value if and only if the fact appears as a "0" in the original HTML/ASCII version. Similarly, if a cell appearing in the original HTML/ASCII version has a "-", that item should not be tagged, which will render a blank field by the rendering engine.