purchases of these securities throughout 2018 and have not sold any securities. The decrease in cash used for acquisitions is due to a year-over-year decrease in the size of the companies acquired. The increase in the cash invested in the Interim Program JV was the result of net origination activity at the Interim Program JV. During the six months ended June 30, 2018, the Interim Program JV had net payoffs of loans, resulting in net distributions. During the six months ended June 30, 2019, the Interim Program JV had net loan originations, resulting in additional capital invested by us in the Interim Program JV.
The change in cash provided by (used in) financing activities was primarily attributable to the change in net warehouse borrowings period to period and increases in repurchases of common stock, cash dividends paid, and proceeds from issuance of common stock, partially offset by an increase in net borrowings of interim warehouse notes payable. The change in net borrowings (repayments) of warehouse borrowings during the first six months of 2019 was due to a smaller increase in the unpaid principal balance of LHFS funded by Agency Warehouse Facilities (as defined below) from December 31, 2018 to June 30, 2019 than from December 31, 2017 to June 30, 2018. During 2019, the unpaid principal balance of LHFS funded by Agency Warehouse Facilities increased $0.1 billion from their December 31, 2018 balance compared to an increase of $0.3 billion during the same period in 2018.
The change in net borrowings of interim warehouse notes payable was principally due to interim loan origination and repayment activity period over period. During 2019, interim loans originated were funded principally from interim warehouse notes payable, and the interim loans that paid off were fully funded with corporate cash, resulting in net borrowings of interim warehouse borrowings. During 2018, the net repayments of interim warehouse notes payable was principally due to the Company’s fully funding a large portfolio of loans held for investment at the end of the second quarter of 2018.
The increase in share repurchase activity was principally related to an increase in the repurchase of shares to settle employee tax obligations for performance-based share awards. No performance-based awards vested during 2018 compared to 489 thousand shares during 2019. The increase in cash dividends paid is primarily related to a 20% increase in the dividends paid per share. The decrease in proceeds from the issuance of common stock is primarily related to a decrease in employee stock options exercised year over year. No options were exercised in 2019 compared to 295 thousand in 2018.
Liquidity and Capital Resources
Uses of Liquidity, Cash and Cash Equivalents
Our significant recurring cash flow requirements consist of (i) short-term liquidity necessary to fund loans held for sale; (ii) liquidity necessary to fund loans held for investment under the Interim Program; (iii) liquidity necessary to pay cash dividends; (iv) liquidity necessary to fund our portion of the equity necessary for the operations of the Interim Program JV; (v) working capital to support our day-to-day operations, including debt service payments and payments for salaries, commissions, and income taxes; and (vi) working capital to satisfy collateral requirements for our Fannie Mae DUS risk-sharing obligations and to meet the operational liquidity requirements of Fannie Mae, Freddie Mac, HUD, Ginnie Mae, and our warehouse facility lenders.
Fannie Mae has established standards for capital adequacy and reserves the right to terminate our servicing authority for all or some of the portfolio if at any time it determines that our financial condition is not adequate to support our obligations under the DUS agreement. We are required to maintain acceptable net worth as defined in the standards, and we satisfied the June 30, 2019 requirements. The net worth requirement is derived primarily from unpaid balances on Fannie Mae loans and the level of risk-sharing. At June 30, 2019, the net worth requirement was $186.0 million and our net worth, as defined in the requirements, was $651.5 million, as measured at our wholly owned operating subsidiary, Walker & Dunlop, LLC. As of June 30, 2019, we were required to maintain at least $36.7 million of liquid assets to meet our operational liquidity requirements for Fannie Mae, Freddie Mac, HUD, Ginnie Mae and our warehouse facility lenders. As of June 30, 2019, we had operational liquidity, as defined in the requirements, of $209.8 million, as measured at our wholly owned operating subsidiary, Walker & Dunlop, LLC.
We paid a cash dividend of $0.30 per share for the first and second quarters of 2019, a 20% increase from the $0.25 per share quarterly dividends paid in 2018. In August 2019, our Board of Directors declared a cash dividend of $0.30 per share for the third quarter of 2019. We expect to continue to make regular quarterly dividend payments for the foreseeable future. Over the past three years, we have returned $136.1 million to investors in the form of the repurchase of 2.1 million shares of our common stock under share repurchase programs for a cost of $86.1 million and cash dividend payments of $50.0 million. Additionally, we have invested $149.8 million in acquisitions and the purchase of MSRs. On occasion, we may use cash to fully fund loans held for investment or loans held for sale instead of using our warehouse lines. As of June 30, 2019, we used corporate cash to fully fund loans held for investment with an unpaid principal balance of $146.0 million and $89.9 million to fully fund loans held for sale. We continually seek opportunities to execute additional acquisitions and purchases of MSRs and complete such acquisitions if the economics of these acquisitions are favorable. In February 2019, our Board of Directors approved a new stock repurchase program that permits the repurchase of up to $50.0 million of shares of our common stock over a 12-month