Property Operating Expenses. Property operating expenses are comprised mainly of building common area and maintenance expenses, insurance, property taxes, property management fees, as well as certain expenses that are not recoverable from tenants, the majority of which are related to costs necessary to maintain the appearance and marketability of vacant space. In the normal course of business, property expenses fluctuate and are impacted by various factors including, but not limited to, occupancy levels, weather, utility costs, repairs, maintenance andre-leasing costs. Property operating expenses increased $2.8 million, or 24%, to $14.5 million for the three months ended June 30, 2019 from $11.7 million for the three months ended June 30, 2018. The increase in property operating expenses was primarily due to the acquisitions described above. The acquisition of the Circle Point, The Quad, Greenwood Blvd, Camelback Square, Canyon Park and Cascade Station contributed an additional $0.9 million, $0.3 million, $0.4 million, $0.4 million, $0.2 million and $0.1 million, respectively, in additional property operating expenses. Park Tower operating expenses also increased by $0.2 million due to the higher occupancy at that property. Plaza 25 decreased by $0.4 million due to the sale of that property in February 2019. The remaining property operating expenses aggregate to a net $0.7 million increase in comparison to the prior-year period.
General and Administrative. General and administrative expenses are comprised of public company reporting costs and the compensation of our management team and board of directors as well asnon-cash stock-based compensation expenses. General and administrative expenses increased $1.4 million, or 71%, to $3.4 million for the three months ended June 30, 2019 compared to $2.0 million for the three months ended June 30, 2018. Of this increase, $1.1 million can be attributed to theone-time expenses and accruals incurred as a result of the assignment fee income earned during the quarter as described above and the balance of the increase is primarily attributable to higher payroll costs.
Depreciation and Amortization. Depreciation and amortization increased $2.8 million, or 24%, to $14.6 million for the three months ended June 30, 2019 compared to $11.8 million for the three months ended June 30, 2018, primarily due to the addition of the Circle Point, The Quad, Greenwood Blvd, Camelback Square, Canyon Park and Cascade Station properties partially offset by a decrease at Plaza 25 due to the sale of the property.
Other Expense (Income)
Interest Expense. Interest expense increased $2.4 million, or 44%, to $7.8 million for the three months ended June 30, 2019, compared to $5.4 million for the three months ended June 30, 2018. The increase was primarily due to interest expense related to acquisitions. Interest expense for the Circle Point, The Quad, Greenwood Blvd, Canyon Park and Cascade Station property level debt increased by $0.5 million, $0.3 million, $0.3 million, $0.4 million and $0.1 million, respectively, and the interest on the line of credit increased by $1.1 million as a result of acquisitions funded by our $250 million Unsecured Credit Facility. These increases were partially offset by a $0.2 million decrease in the Plaza 25 debt as a result of its sale and the extinguishment of its property level debt.
Comparison of Six Months Ended June 30, 2019 to Six Months Ended June 30, 2018
Rental and Other Revenues. Revenue includes net rental income, including parking, signage and other income, as well as the recovery of operating costs and property taxes from tenants. Rental and other revenues increased $16.5 million, or 27%, to $78.3 million for the six months ended June 30, 2019 compared to $61.8 million for the six months ended June 30, 2018. Of this increase, $1.8 million was attributable to the acquisition of Pima Center in April 2018, $4.1 million from the acquisition of Circle Point in July 2018, $2.8 million from the acquisition of The Quad in July 2018, $2.3 million from the acquisition of Greenwood Blvd in December 2018, $2.4 million from the acquisition of Camelback Square in December 2018, $2.0 million from the acquisition of Canyon Park in February 2019 and $0.2 million from the acquisition of Cascade Station in June 2019. Revenue from Central Fairwinds, Park Tower, Mission City and FRP Collection also increased by $0.4 million, $0.7 million, $0.4 million and $0.3 million, respectively, as a result of increased average occupancy over the prior year. Partially offsetting these increases, Washington Group Plaza decreased by $1.7 million due to the sale of the property in March 2018 and Plaza 25 decreased by $1.0 million due to the sale of the property in February 2019. Revenue from DTC Crossroads decreased $0.4 million as a result of decreased occupancy over the prior year and Sorrento Mesa also decreased by $1.2 million as a result of the termination fee payment received in the prior year. The remaining properties’ revenues were modestly higher in comparison to the prior year primarily as a result of modestmark-to-market increases in rents upon renewal. Other Revenues benefited from aone-time payment of $2.6 million received as consideration for the assignment of a purchase contract. The assignment fee originated through our administrative services relationship. Upon adoption of Topic 842, prior year amounts disclosed in rental income, expense reimbursement, and other have been combined into a single line to conform to current period presentation.
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