to an interest-only strip security that was near maturity. Related impairment charges of $3.1 million were also recorded in provision for credit losses on the income statement. Unrealized losses (tax-effected) on the available-for-sale portfolio totaled $12.7 million as of December 31, 2024, compared to $0.7 million as of September 30, 2024. Unrecognized losses (tax-effected) on the held-to-maturity portfolio totaled $53.6 million as of December 31, 2024, compared to $41.8 million as of September 30, 2024. Combined unrealized and unrecognized losses (tax-effected) on the available-for-sale and held-to-maturity portfolios totaled $66.3 million, or 3.27% of the combined portfolios as of December 31, 2024, compared to $42.5 million or 2.08% of the combined portfolios as of September 30, 2024. The increase in unrealized and unrecognized losses (tax-effected) was largely driven by the sharp rise in yields on mortgage-backed securities following the end of the third quarter.
Investment securities portfolio average yield was 4.41% in the quarter, compared to 4.23% in the prior quarter and 3.84% in the fourth quarter of 2023.
Deposits and Borrowings
Deposits were $9.9 billion as of December 31, 2024, compared to $10.3 billion as of September 30, 2024, and $10.7 billion as of December 31, 2023. The decrease in deposits from the prior quarter was largely due to a $488 million decrease in higher-cost brokered deposits achieved following the $489 million sale of loans held for sale. Certificates of deposit accounted for 24% of total deposits as of December 31, 2024, compared to 25% and 29% as of September 30, 2024, and December 31, 2023, respectively. Core deposits accounted for 67% of total deposits as of December 31, 2024, compared to 64% and 60% as of September 30, 2024, and December 31, 2023, respectively. Brokered deposits accounted for 33% of total deposits as of December 31, 2024, compared to 36% and 40% as of September 30, 2024, and December 31, 2023, respectively.
Cost of deposits was 3.19% for the quarter, compared to 3.41% for both the prior and year-ago quarters.
Insured and collateralized deposits accounted for approximately 84% of total deposits as of December 31, 2024, compared to 85% from the prior quarter.
Our loan to deposit ratio measured 93.5% as of December 31, 2024, compared to 95.9% and 95.2% as of September 30, 2024, and December 31, 2023, respectively.
Borrowings were $1.4 billion as of December 31, 2024, compared to $1.7 billion and $1.4 billion as of September 30, 2024, and December 31, 2023, respectively. Average borrowings outstanding were $1.5 billion or 11.5% of average assets for the quarter, compared to $1.7 billion or 12.6% of average assets for the prior quarter and $1.1 billion or 8.6% for the fourth quarter of 2023. The weighted average rate paid on borrowings was 4.14% for the quarter, compared to 4.04% for the prior quarter and 4.07% for the fourth quarter of 2023. During the quarter, $266.6 million in borrowings at a rate of 4.76% from the Bank Term Funding Program (“BTFP”) at the Federal Reserve Bank were repaid in full.
As of December 31, 2024, our unused borrowing capacity was $3.0 billion, which consists of available lines of credit with the FHLB and other correspondent banks as well as access to the Federal Reserve Bank’s discount window.
Private Wealth Management and Trust Assets
Our AUM balance was $5.4 billion as of December 31, 2024, compared to $5.5 billion from the prior quarter, and $5.2 billion as of December 31, 2023. Activity within the AUM balance during the quarter consisted of the following: $91 million of new accounts; $38 million of net withdrawals; and $107 million of performance losses. AUA at FFB’s Trust Department was $1.1 billion as of December 31, 2024, compared to $1.2 billion in the prior quarter and $1.3 billion at December 31, 2023.