Each authorized insurer, and each formerly authorized insurer with respect to premiums written while an authorized insurer in this state, shall file with the director, on or before March 1 in each year, a report of all insurance business written or contracted in the state, with proper proportionate allocation of premium for the property, subjects, or risks in the state insured under policies or contracts covering property, subjects, or risks located or resident in more than one state, during the preceding year ending December 31.