An insurer formed in this State shall be either:
(1) An incorporated stock insurer,
(2) An incorporated mutual insurer which charges for and collects in advance cash premiums in an amount adequate to maintain full legal reserves and to fully meet and discharge all of its obligations and liabilities under its policies without assessments or calls upon its members for additional premium, except as provided in this article relative to the contingent liability of its members, or
(3) A reciprocal insurer, with respective powers, duties and restrictions as provided in this article.