A Hidden Party indicates a confidential case. The court only marks Parties as "Hidden" or "Confidential" after a case has been assigned a level of confidentiality due to either the nature of the case or due to the case involving juvenile parties.
If you have unrestricted access to a given case that shows parties marked as "Confidential" or "Hidden Party", please contact the clerks at the court your case is filed into to have them check or edit your case access rights.