charge-offs in our indirect automobile book which grew by $27.1 million, or 8.0%, in loan balances between periods and was further impacted by the economic environment as a result of the COVID-19 pandemic.
Non-interest income totaled $1.8 million for the three months ended June 30, 2020; an increase of $317,000, or 22.1%, from the comparable period in the prior year. Net gain on the sale of loans increased $690,000, or 274.9% which was offset by a $219,000 decrease in service charges on deposit accounts, a $79,000 decrease in investment advisory income and a $110,000 decrease in other non-interest income. Non-interest income increased $613,000, or 22.7%, to $3.3 million for the six months ended June 30, 2020. In the six months ended June 30, 2020, net gain on the sale of loans increased $989,000, or 237.2% while investment advisory income increased $20,000 to $562,000. These increases were offset by a $265,000 decrease in service charges on deposit accounts and a $124,000 decrease in other non-interest income affected primarily by the amortization of mortgage servicing rights.
For the second quarter of 2020, non-interest expenses decreased $283,000, or 4.0%, to $6.8 million over the comparable 2019 period. The decrease was primarily due to decreased automobile loan expenses as automobile lending volume decreased as a result of COVID-19. Fees such as dealer loan fees, appraisal and loan review fees were all substantially lower during the second quarter of 2020. For the six months ended June 30, 2020, non-interest expenses increased $98,000, or 0.7%, to $14.1 million over the comparative six-month period in 2019. Salaries and benefits increased $317,000, or 4.0%, which was primarily attributable to annual merit increases, production incentives and employee benefit expense increases. This increase was substantially offset by the decreased automobile loan fees described above.
Balance Sheet Analysis
Total assets were $1.1 billion at June 30, 2020, representing an increase of $154.4 million, or 15.9%, from $973.9 million at December 31, 2019. Cash and due from banks increased $62.6 million from December 31, 2019, to $74.6 million, primarily due to an increase in deposits held at the Federal Reserve Bank of New York. Net loans increased $93.8 million, or 11.8%, and included $89.1 million of outstanding SBA PPP loan balances and a $4.9 million increase on our indirect automobile portfolio. Other assets also include the right-of-use asset of $6.5 million at June 30, 2020 due to the adoption of the Accounting Standards Update 2016-02, Leases (Topic 842).
Past due loans increased $5.7 million, or 32.6%, between December 31, 2019 and June 30, 2020 finishing at $23.3 million, or 2.6%, of total loans, up from 2.2% at year-end 2019. During the same timeframe, non-performing assets increased $1.0 million or 9.7%, to $11.3 million. Our reserve as a percentage of total gross loans was 0.96% at June 30, 2020 as compared to 0.75% at December 31, 2019.
During the first six months of 2020, total liabilities increased $150.6 million, or 17.4%, to $1.0 billion, mainly due to a $136.7 million increase in deposits due to the inflow of cash from PPP loans and an apparent flight to safety as investors fled the stock market volatility. The establishment of a $6.5 million lease liability, an increase of $4.8 million in Federal Home Loan Bank and Federal Reserve Bank advances and a $3.3 million increase in mortgagors’ escrow accounts also contributed to the increase in liabilities.
Stockholders' equity increased $3.8 million to $113.7 million at June 30, 2020, primarily due to net income of $2.4 million and a net unrealized gain on available for sale securities. The Company's ratio of average equity to average assets was 10.80% for the six months ended June 30, 2020 and 11.24% for the six months ended June 30, 2019.