An insurer may deposit and maintain on deposit with the commissioner funds and eligible securities in amount exceeding its required deposit under this code by not more than one hundred thousand dollars, for the purpose of absorbing fluctuations in the value of securities held in its required deposit, and to facilitate the exchange and substitution of such required securities. During the solvency of the insurer any such excess deposit or any part thereof shall be released to it upon its request. During the insolvency of the insurer such excess deposit shall be released only as provided in RCW
48.16.100.