Utah Code § 31A-21-306

Two or more insurers may together issue a policy or surety bond. Their liability shall be joint and several with respect to the policy or bond. The policy or bond shall state the proportion or amount of premium to be paid to each insurer and, as between the issuing insurers, the type and the proportion or amount of liability each insurer assumes. Service of process on any of the insurers is service on all of them.