All investments of insurers authorized to do business in this State, for which no rule or method of valuation has been otherwise provided, must be valued in the discretion of the director or his designee at their fair market value, appraised value, or at amounts determined by the director or his designee as their fair market value. If any valuation of an investment by an insurer appears to be an unreasonable estimate of its true value, the director or his designee has the authority to cause the investment to be appraised, and the appraised value must be substituted as the true value. The appraisal must be made by two disinterested and competent persons, one to be appointed by the director and one to be appointed by the insurer. In the event these two persons fail to agree, they shall appoint a third disinterested and competent person, and the estimate of the value of the investment, as arrived at by these three persons, must be substituted as the true value.