result of the repayment of the secured borrowing in the second quarter of 2021, a unique transaction. Cash dividends paid increased as a result of the increase in our dividend to $0.50 per share in 2021 compared to $0.36 per share in 2020. Net borrowings of interim warehouse notes payable increased due to the increase in originations of loans held for investments noted above. The decrease in cash paid for repurchases of common stock was related to repurchases under approved stock repurchase programs. In 2021, we did not repurchase any shares under approved repurchase programs, while in 2020 we repurchased $23.7 million of shares under such programs.
Liquidity and Capital Resources
Uses of Liquidity, Cash and Cash Equivalents
Our significant recurring cash flow requirements consist of liquidity to (i) fund loans held for sale; (ii) fund loans held for investment under the Interim Loan Program; (iii) pay cash dividends; (iv) fund our portion of the equity necessary for the operations of the Interim Program JV, the Appraisal JV, and other equity-method investments; (v) meet working capital needs to support our day-to-day operations, including debt service payments, servicing advances and payments for salaries, commissions, and income taxes; and (vi) meet working capital needs 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 benchmark 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 requirements as of September 30, 2021. The net worth requirement is derived primarily from unpaid balances on Fannie Mae loans and the level of risk-sharing. As of September 30, 2021, the net worth requirement was $250.2 million, and our net worth was $1.1 billion, as measured at our wholly owned operating subsidiary, Walker & Dunlop, LLC. As of September 30, 2021, we were required to maintain at least $49.5 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 September 30, 2021, we had operational liquidity of $254.7 million, as measured at our wholly owned operating subsidiary, Walker & Dunlop, LLC.
We paid a cash dividend of $0.50 per share in each of the first three quarters of 2021, which is 39% higher than the quarterly dividend paid in each of the first three quarters of 2020. On November 3, 2021, our Board of Directors declared a dividend of $0.50 per share for the fourth quarter of 2021. The dividend will be paid on November 29, 2021 to all holders of record of the Company’s restricted and unrestricted common stock as of November 19, 2021.
Over the past three years, we have returned $210.7 million to investors in the form of the repurchase of 1.5 million shares of our common stock under share repurchase programs for a cost of $72.0 million and cash dividend payments of $138.7 million. Additionally, we have invested $179.0 million in acquisitions. On occasion, we may use cash to fully fund some loans held for investment or loans held for sale instead of using our warehouse lines. As of September 30, 2021, we used corporate cash to fully fund loans held for investment with an unpaid principal balance of $53.0 million. We continually seek opportunities to complete additional acquisitions if we believe the economics are favorable.
In February 2021, our Board of Directors approved a stock repurchase program that permits the repurchase of up to $75 million of shares of our common stock over a 12-month period beginning February 12, 2021. Through September 30, 2021 we have not repurchased any shares under the 2021 repurchase program and have $75.0 million of remaining capacity under that program.
Historically, our cash flows from operations and warehouse facilities have been sufficient to enable us to meet our short-term liquidity needs and other funding requirements. We believe that cash flows from operations will continue to be sufficient for us to meet our current obligations for the foreseeable future.
Restricted Cash and Pledged Securities
Restricted cash consists primarily of good faith deposits held on behalf of borrowers between the time we enter into a loan commitment with the borrower and the investor purchases the loan. We are generally required to share the risk of any losses associated with loans sold under the Fannie Mae DUS program, our only off-balance sheet arrangement. We are required to secure this obligation by assigning collateral to Fannie Mae. We meet this obligation by assigning pledged securities to Fannie Mae. The amount of collateral required by Fannie Mae is a formulaic calculation at the loan level and considers the balance of the loan, the risk level of the loan, the age of the loan, and the level of risk-sharing. Fannie Mae requires collateral for Tier 2 loans of 75 basis points, which is funded over a 48-month period that begins upon delivery