The subsidiary banks have a variety of sources of short-term liquidity available to them, including federal funds purchased from correspondent banks, FHLB advances, wholesale structured repurchase agreements, brokered deposits, lines of credit, borrowing at the Federal Reserve Discount Window, sales of securities AFS, and loan/lease participations or sales. The Company also generates liquidity from the regular principal payments and prepayments made on its loan/lease portfolio, and on the regular monthly payments on its securities portfolio.
At June 30, 2021, the subsidiary banks had 28 lines of credit totaling $639.8 million, of which $183.8 million was secured and $456.0 million was unsecured. At June 30, 2021, the full $639.8 million was available.
At December 31, 2020, the subsidiary banks had 28 lines of credit totaling $743.1 million, of which $287.1 million was secured and $456.0 million was unsecured. At December 31, 2020, the full $743.1 million was available.
The Company has emphasized growing the number and amount of lines of credit in an effort to strengthen this contingent source of liquidity. Additionally, the Company maintains a $25.0 million secured revolving credit note with a variable interest rate and a maturity of June 30, 2022. At June 30, 2021, the full $25.0 million was available.
As of June 30, 2021, the Company had $684.0 million in average correspondent banking deposits spread over 186 relationships. While the Company believes that these funds are relatively stable, there is the potential for large fluctuations that can impact liquidity. Seasonality and the liquidity needs of these correspondent banks can impact balances. Management closely monitors these fluctuations and runs stress scenarios to measure the impact on liquidity and interest rate risk with various levels of correspondent deposit run-off.
Investing activities used cash of $143.4 million during the first six months of 2021, compared to $557.6 million for the same period of 2020. The net increase in interest-bearing deposits at financial institutions was $844 thousand for the first six months of 2021, compared to a net decrease of $7.1 million for the same period of 2020. Proceeds from calls, maturities, and paydowns of securities were $110.9 million for the first six months of 2021, compared to $34.5 million for the same period of 2020. Purchases of securities used cash of $108.6 million for the first six months of 2021, compared to $166.7 million for the same period of 2020. Proceeds from sales of securities were $23.9 million for the first six months of 2021, compared to $4.6 million for the same period of 2020. The net increase in loans/leases used cash of $171.0 million for the first six months of 2021 compared to $447.4 million for the same period of 2020.
Financing activities provided cash of $104.9 million for the first six months of 2021, compared to $530.6 million for same period of 2020. Net increases in deposits totaled $89.8 million for the first six months of 2021, compared to $409.0 million for the same period of 2020. During the first six months of 2021, the Company's short-term borrowings increased $1.6 million, compared to an increase in short-term borrowings of $111.4 million for the same period of 2020. There were no long-term FHLB advances during the first six months of 2021. There were no maturities and principal payments on FHLB term advances in the first six months of 2021. Net increase in overnight advances totaled $25.0 million for the first six months of 2021. In the first six months of 2020, the Company decreased short-term and overnight FHLB advances by $40.0 million. Prepayments on brokered and public time deposits totaled $29.2 million during the first six months of 2020. Prepayment of subordinated notes totaled $5.0 million during the first six months of 2021.
Total cash provided by operating activities was $32.7 million for the first six months of 2021, compared to $39.3 million for the same period of 2020.
Throughout its history, the Company has secured additional capital through various sources, including the issuance of common and preferred stock, as well as trust preferred securities and, most recently, subordinated notes.
The Company (on a consolidated basis) and the subsidiary banks are subject to various regulatory capital requirements administered by the federal banking agencies. Failure to meet minimum capital requirements can initiate certain mandatory and possibly additional discretionary actions by regulators that, if undertaken, could have a direct material effect on the Company and subsidiary banks' financial statements. Refer to Note 9 of the Consolidated Financial Statements for additional information regarding regulatory capital.