public X12StreamReader(Stream stream, Encoding encoding)
 {
     _reader = new StreamReader(stream, encoding);
     char[] header = new char[106];
     if (_reader.Read(header, 0, 106) < 106)
         throw new ArgumentException("ISA segment and terminator is expected to be at least 106 characters.");
     _delimiters = new X12DelimiterSet(header);
     _isaSegment = new string(header);
 }