Debt Securities Portfolio. Securities available-for-sale increased $20.1 million, or 16.4%, to $142.2 million at March 31, 2024 from $122.1 million at December 31, 2023, driven by purchases of $25.0 million, partially offset by paydowns of $3.3 million and unrealized losses of $1.6 million. Securities held-to-maturity decreased $1.8 million, or 2.3%, to $75.2 million at March 31, 2024 from $77.0 million at December 31, 2023, driven by paydowns of $1.7 million and premium amortization of $24 thousand.
Funding. Total deposits increased $26.8 million, or 1.9%, to $1.43 billion at March 31, 2024 from $1.41 billion at December 31, 2023. We continue to focus on the acquisition and expansion of core deposit relationships. Core deposits, which we define as total deposits excluding time deposits, totaled $1.42 billion at March 31, 2024, or 99.0% of total deposits, compared to $1.40 billion or 99.4% of total deposits at December 31, 2023. Litigation and payment processing deposits represent $1.24 billion, or 87%, of total deposits at March 31, 2024. Savings, NOW and money market deposits increased $20.8 million, or 2.2%, to $947.1 million at March 31, 2024.
Core commercial relationship banking clients in our two national verticals represent approximately 87% of our $1.43 billion deposit base at March 31, 2024. These relationship banking clients are derived from coupling lending facilities, payment processing, and other unique custodial banking needs with commercial cash management depository services. Our deposit strategy primarily focuses on developing full service commercial banking relationships with our clients through lending facilities, payment processing, and other unique commercial cash management services in our two national verticals, rather than competing with other institutions on rate. Our longer duration interest on lawyer trust accounts (“IOLTA”), escrow and claimant trust settlement deposits represent $709.5 million, or 49.5%, of total deposits. As of March 31, 2024, uninsured deposits were $369.4 million, or 26%, of our total deposits of $1.43 billion, excluding $10.6 million of affiliate deposits held by the Bank. Approximately 80% of our uninsured deposits represent clients with full relationship banking (loans, payment processing, and other service-oriented relationships) including, but not limited to, law firm operating accounts, law firm IOLTA/escrow accounts, merchant reserves, ISO reserves, ACH processing, and custodial accounts.
Due to the nature of our larger mass tort and class action settlements related to the litigation vertical, we participate in FDIC insured sweep programs as well as treasury secured money market funds. As of March 31, 2024, off-balance sheet sweep funds totaled approximately $466.6 million, of which approximately $290.9 million, or 62.3%, was available to be swept onto our balance sheet as reciprocal client relationship deposits. Our deposit growth and off-balance sheet funds continue to demonstrate our highly efficient branchless and technology enabled deposit platforms.
At March 31, 2024, we had the ability to borrow a total of $300.1 million from the Federal Home Loan Bank of New York. We also had an available line of credit with the Federal Reserve Bank of New York discount window of $55.9 million. No borrowing amounts were outstanding as of March 31, 2024. Historically, we have never leveraged our balance sheet to generate earnings and have always utilized core client deposits to fund our asset growth and related earnings.
Stockholders’ Equity. Total stockholders’ equity increased $8.5 million to $207.1 million at March 31, 2024, from $198.6 million at December 31, 2023, primarily due to net income of $10.1 million and amortization of share-based compensation of $967 thousand, partially offset by dividends declared to common stockholders of $1.2 million and other comprehensive loss of $1.1 million due to the decrease in fair value of our available-for-sale securities portfolio.
Asset Quality. Nonperforming assets consisted of one multifamily loan totaling $10.9 million as of March 31, 2024 and December 31, 2023. We had no exposure to commercial office space, no construction loans, and only $15.3 million in performing loans to the hospitality industry. The allowance for credit losses was $17.5 million, or 1.43% of total loans, as of March 31, 2024, as compared to $16.6 million, or 1.38% of total loans at December 31, 2023. The increase in the allowance as a percentage of loans was general reserve driven considering loan growth and qualitative factors associated with the current uncertain economic environment including, but not limited to, its potential impact on the New York Metro commercial real estate market. At March 31, 2024, special mention and substandard loans totaled $4.0 million and $10.9 million, respectively, substantially unchanged from December 31, 2023. The ratio of nonperforming loans to total loans and total assets was 0.89% and 0.66%, respectively, as of March 31, 2024, as compared to 0.91% and 0.68%, respectively, as of December 31, 2023. The allowance for credit losses to the nonperforming loans was 160% as of March 31, 2024, as compared to 152% as of December 31, 2023.