(a) In this section, "net direct premium" means the gross direct premium written and reported by an insurer on annual financial statements on:
(1) an insurance policy described by Section 2007.001(2), other than a commercial multiple peril policy; and
(2) the nonliability portion of a commercial multiple peril policy.
(b) Each insurer shall pay a portion of the assessment in the proportion that the insurer's net direct premiums for the period for which the assessment is made bear to the aggregate net direct premiums written in this state by all insurers for that period.