Как насчет этого?
def getData(xml):
# Processing your XML data after block reading.
pass
with open('0000051143-13-000007.txt', 'r') as file: # data.xml is your xml file path
lines = []
flag = False
for line in file:
if line.find('</XBRL>')>=0:
getData("".join(lines))
flag = False
lines = []
if flag or line.find('<?xml ')>=0:
flag = True
lines.append(line)