NONINTEREST EXPENSE
Noninterest expense decreased $579,000 to $107.9 million for the fourth quarter of 2023 from $108.5 million in the prior quarter, primarily driven by a decrease in other expenses due to costs associated with our strategic cost savings initiatives in the third quarter and lower merger-related costs associated with our pending merger with American National in the fourth quarter, partially offset by an increase in FDIC assessment premiums and other insurance due to a special assessment fee incurred in the fourth quarter and an increase in legal reserve related to our previously disclosed settlement with the CFPB (included in other expenses).
Adjusted operating noninterest expense,(1) which excludes amortization of intangible assets ($2.1 million in the fourth quarter and $2.2 million in the third quarter), a FDIC special assessment ($3.4 million recognized in the fourth quarter), the legal reserve related to our previously disclosed settlement with the CFPB ($3.3 million in the fourth quarter), merger-related costs associated with our pending merger with American National ($1.0 million in the fourth quarter and $2.0 million in the third quarter), and expenses associated with strategic cost savings initiatives ($8.7 million in the third quarter), increased $2.5 million to $98.2 million for the fourth quarter from $95.7 million in the prior quarter, primarily due to a $1.2 million increase in other expenses reflecting an increase in OREO and credit related expenses, higher teammate training and travel expenses, and annual debit card inventory purchases, a $1.1 million increase in professional services expense primarily in support of strategic initiatives in the fourth quarter and higher legal fees, a $799,000 increase in marketing and advertising expense primarily due to annual customer disclosure mailings, and a $591,000 increase in occupancy expense driven by the increased lease payments related to the sale-leaseback transaction executed in the third quarter. These increases were partially offset by a $763,000 decrease in salaries and benefits, reflecting the impact of headcount reductions from our strategic cost savings initiatives.
INCOME TAXES
The effective tax rate for the three months ended December 31, 2023 and 2022 was 14.9% and 14.3%, respectively, and the effective tax rate for the years ended December 31, 2023 and 2022 was 15.9% and 16.2%, respectively. The changes in the effective tax rate for the quarter ended and year ended December 31, 2023, compared to December 31, 2022 are primarily driven by the changes in the proportion of tax-exempt income to pre-tax income.
BALANCE SHEET
At December 31, 2023, total assets were $21.2 billion, an increase of $430.0 million or approximately 8.2% (annualized) from September 30, 2023, and an increase of $705.1 million or approximately 3.4% from December 31, 2022. Total assets increased from the prior quarter primarily due to a $351.4 million increase in LHFI (net of deferred fees and costs). In addition, investment securities increased $151.1 million primarily due to a decrease in unrealized losses in the AFS securities portfolio due to the impact of declining market interest rates. Total assets increased from the same period in the prior year primarily due to a $1.2 billion increase in LHFI (net of deferred fees and costs), partially offset by a $525.7 million decrease in investment securities due primarily to the sale of AFS securities in the first quarter of 2023.
At December 31, 2023, LHFI (net of deferred fees and costs) totaled $15.6 billion, an increase of $351.4 million or 9.1% (annualized) from $15.3 billion at September 30, 2023, and an increase of $1.2 billion or 8.2% from December 31, 2022. Quarterly average LHFI (net of deferred fees and costs) totaled $15.4 billion at December 31, 2023, an increase of $254.7 million or 6.7% (annualized) from the prior quarter, and an increase of $1.3 billion or 9.0% from December 31, 2022. LHFI (net of deferred fees and costs) increased from both the prior quarter and the prior year, primarily due to increases in the commercial and industrial and the multifamily real estate portfolios.
At December 31, 2023, total investments were $3.2 billion, an increase of $151.1 million from September 30, 2023 and a decrease of $525.7 million from December 31, 2022. AFS securities totaled $2.2 billion at December 31, 2023, $2.1 billion at September 30, 2023, and $2.7 billion at December 31, 2022. Total net unrealized losses on the AFS securities portfolio were $384.3 million at December 31, 2023, compared to $523.1 million at September 30, 2023 and $462.5 million at December 31, 2022. Held to maturity securities are carried at cost and totaled $837.4 million at December 31, 2023, $843.3 million at September 30, 2023, and $847.7 million at December 31, 2022 and had net unrealized losses of