Parsing xbrl data using python

Hi - please could you let me know of a good resource for understanding how to parse company information using the python xbrl library?

I can parse data using:

from xbrl import XBRLParser
xbrl_parser = XBRLParser()
xbrl = xbrl_parser.parse(open("%s/%s" % (fold,f)))
gaap_obj = xbrl_parser.parseGAAP(xbrl,
doc_date=“20180331”,
context=“current”,
ignore_errors=0)

but the returned GAAP object contains zeros for all the accounting entries.

Is there a better library or different parser I should be using?