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 $2.2 million, or 19%, to $13.8 million for the three months ended March 31, 2019 from $11.6 million for the same period in 2018. The increase in property operating expenses was primarily due to the acquisitions described above. The acquisition of the Pima Center, Circle Point, The Quad, Greenwood Blvd, Camelback Square and Canyon Park contributed an additional $0.6 million, $1.0 million, $0.4 million, $0.4 million, $0.3 million and $0.1 million in additional property operating expenses, respectively. Washington Group Plaza decreased by $0.8 million due to the sale of that property in March 2018 and Plaza 25 decreased by $0.2 million due to the sale of that property in February 2019. The remaining property operating expenses aggregate to an overall $0.4 million increase in comparison to the prior year.
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 $0.3 million, or 16%, to $2.3 million for the three months ended March 31, 2019 compared to $2.0 million for the same period in 2018. The increase was primarily attributable to higher payroll costs.
Depreciation and Amortization. Depreciation and amortization increased $2.5 million, or 21%, to $14.4 million for the year ended March 31, 2019 compared to $11.9 million for the same period in 2018, primarily due to the addition of the Papago Tech, Pima Center, Circle Point, The Quad, Greenwood Blvd, Camelback Square and Canyon Park properties offset by a decrease at Washington Group Plaza and Plaza 25 due to the sale of those properties.
Other Expense (Income)
Interest Expense. Interest expense increased $1.7 million, or 29%, to $7.5 million for the three months ended March 31, 2019, compared to $5.8 million for the corresponding period in 2018. The increase was primarily due to interest expense related to acquisitions. Interest expense for the Circle Point, The Quad, Greenwood Blvd and Canyon Park property level debt increased by $0.5 million, $0.3 million, $0.3 million and $0.1 million, respectively, and the interest on the line of credit increased by $0.9 million as a result of acquisitions funded by our $250 million Unsecured Credit Facility (“Unsecured Credit Facility”). These increases were offset by a $0.2 million and $0.2 million, respective decrease in the Washington Group Plaza and Plaza 25 debt as a result of the sale of those properties and the extinguishment of its property level debt.
Cash Flows
Comparison of Three Months Ended March 31, 2019 to Three Months Ended March 31, 2018
Cash, cash equivalents and restricted cash were $37.0 million and $38.9 million as of March 31, 2019 and March 31, 2018, respectively.
Cash flow from operating activities.Net cash provided by operating activities increased by $1.0 million to $2.8 million for the three months ended March 31, 2019 compared to $1.8 million for the same period in 2018. The increase was primarily attributable to increased operating cash flows from acquisitions.
Cash flow to investing activities. Net cash used in investing activities increased by $117.7 million to $36.7 million for the three months ended March 31, 2019 compared to $81.0 million provided by investing activities for the same period in 2018. The increase in cash used in investing activities was primarily due to the acquisition of Canyon Park in the first quarter 2019. Additionally, we realized lower proceeds from the sale of real estate in the first quarter 2019 compared to the first quarter 2018, which included proceeds from the sale of Washington Group Plaza in 2018.
Cash flow from financing activities.Net cash provided by financing activities increased by $116.7 million to $37.8 million for the three months ended March 31, 2019 compared to $78.9 million used in financing activities in the same period in 2018. Cash flow provided by financing activities increased primarily due to higher net proceeds from mortgage loans and credit facility borrowings in 2019 compared to 2018.
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