during the nine months ended September 30, 2020, compared to $3.6 million for the same period in 2019, and $1.2 million of expense from properties that include tenants with gross leases.
Management Fees Expense - related party
Management fee expense for the nine months ended September 30, 2020 was $4.0 million, compared to $4.5 million for the same period in 2019, a decrease of $0.5 million. As a result of the Internalization, management fee expense was incurred for the first six months of the current nine-month period compared to a full nine months during the same period in 2019. This fee was calculated based on our stockholders’ equity balance.
Depreciation Expense
Depreciation expense for the nine months ended September 30, 2020 was $19.4 million, compared to $13.5 million for the same period in 2019, an increase of $5.9 million. The increase results primarily from depreciation expense incurred on the facilities we acquired subsequent to September 30, 2019, as well as from the recognition of a full nine months of depreciation expense in 2020 from acquisitions that were completed during the nine months ended September 30, 2019.
Amortization Expense
Amortization expense for the nine months ended September 30, 2020 was $6.8 million, compared to $3.8 million for the same period in 2019, an increase of $3.0 million. The increase results primarily from amortization expense incurred on intangible assets recorded subsequent to September 30, 2019, as well as from the recognition of a full nine months of amortization expense in 2020 from intangible assets recorded during the nine months ended September 30, 2019.
Interest Expense
Interest expense for the nine months ended September 30, 2020 was $13.6 million, compared to $12.7 million for the same period in 2019, an increase of $0.9 million. This increase was primarily due to higher average borrowings during the nine months ended September 30, 2020, compared to the same period last year, the proceeds of which were used to partially finance our property acquisitions during that time period.
The weighted average interest rate of our debt for the nine months ended September 30, 2020 was 3.48%. Additionally, the weighted average interest rate and term of our debt was 3.34% and 3.06 years at September 30, 2020.
Management Internalization Expense
Management internalization expense for the nine months ended September 30, 2020 was $14.0 million, compared to zero for the same period in 2019. This expense represents a one-time expense of $12.1 million related to the settlement of a preexisting contractual relationship and $1.9 million of professional fees associated with the Internalization.
Net (Loss) Income
Net loss for the nine months ended September 30, 2020 was $(5.1) million compared to net income of $6.8 million for the same period in 2019, a decrease of $11.9 million. The decrease resulted primarily from the recognition of $14.0 million of management internalization expense and the increase in expenses for the current nine-month period, partially offset from an increase in rental revenue over the period.
Assets and Liabilities
As of September 30, 2020 and December 31, 2019, our principal assets consisted of investments in real estate, net, of $977.5 million and $849.0 million, respectively. Our liquid assets consisted primarily of cash and cash equivalents and restricted cash of $7.3 million and $7.2 million, as of September 30, 2020 and December 31, 2019, respectively.
The increase in our investments in real estate, net, to $977.5 million as of September 30, 2020 compared to $849.0 million as of December 31, 2019, was the result of the 10 acquisitions that we completed during the nine months ended September 30, 2020.