An insurer may so deposit cash or eligible securities in an amount exceeding its deposit required or otherwise permitted under this Code, for the purpose of absorbing fluctuations in the value of securities held in its deposit, and to facilitate the exchange and substitution of securities deposited. During the solvency of the insurer any such excess deposit or part thereof shall be released to the insurer upon its request. During the insolvency of the insurer such excess deposit shall be released only as provided in Section 1707 of this article.