A domestic mutual insurer on the cash premium plan shall at all times have and maintain surplus funds, representing the excess of its assets over its liabilities, in amount not less than the aggregate of

(1) the amount of any surplus funds deposited by it with the commissioner to qualify for its original certificate of authority, and

(2) the amount of any additional surplus required of it pursuant to RCW 48.09.090 for authority to transact additional kinds of insurance.