we are closely monitoring the impact of the covid-19 pandemic on all aspects of our business , including how it is impacting our tenants , employees , and business partners . adverse changes in economic conditions , including the ongoing effects of the global covid-19 pandemic , could result in a reduction of the availability of financing and potentially in higher borrowing costs . vacancy rates may increase , and rental rates and rent collection rates may decline , beyond 2020 as the current economic climate may negatively impact tenants . overall economic conditions , including but not limited to higher unemployment and deteriorating financial and credit markets , could have a dampening effect on the fundamentals of our business , including increases in past due accounts , tenant defaults , lower occupancy and reduced effective rents . the ongoing covid-19 pandemic has significantly slowed global economic activity , caused significant volatility in financial markets , and resulted in unprecedented job losses . in addition , the government responses to control the pandemic are creating disruption in the global economy and supply chains and adversely impacting many industries , including owners and developers of office and mixed-use building . these adverse conditions have impacted our net income and cash flows and could have a material adverse effect on our financial condition . we believe that the quality of our assets and the strength of our balance sheet will enable us to raise debt capital , if necessary , in various forms and from different sources , including through secured or unsecured loans from banks , pension funds and life insurance companies . however , there can be no assurance that we will be able to borrow funds on terms that are economically attractive or at all . we continue to seek revenue growth throughout our portfolio by increasing occupancy and rental rates . occupancy at our core properties at december 31 , 2020 was 91.9 % compared to 93.0 % at december 31 , 2019 . 28 the table below summarizes selected operating and leasing statistics of our wholly owned operating properties for the years ended december 31 , 2020 and 2019 : replace_table_token_5_th ( 1 ) does not include properties under development , redevelopment , held for sale , or sold . ( 2 ) includes leasing related to completed developments and redevelopments , as well as sold properties . ( 3 ) calculated as percentage of total square feet . ( 4 ) includes base rent plus reimbursement for operating expenses and real estate taxes . ( 5 ) calculated on a weighted average basis . in seeking to increase revenue through our operating , financing , and investment activities , we also seek to minimize operating risks , including ( i ) tenant rollover risk , ( ii ) tenant credit risk and ( iii ) development risk . tenant rollover risk : we are subject to the risk that tenant leases , upon expiration , will not be renewed , that space may not be relet , or that the terms of renewal or reletting ( including the cost of renovations ) may be less favorable to us than the current lease terms . leases that accounted for approximately 7.1 % of our aggregate final annualized base rents as of december 31 , 2020 ( representing approximately 9.5 % of the net rentable square feet of the properties ) are scheduled to expire without penalty in 2021. we maintain an active dialogue with our tenants in an effort to maximize lease renewals . if we are unable to renew leases or relet space under expiring leases , at anticipated rental rates , or if tenants terminate their leases early , our results of operations and cash flow would be adversely impacted . tenant credit risk : in the event of a tenant default , we may experience delays in enforcing our rights as a landlord and may incur substantial costs in protecting our investment . our management regularly evaluates our accounts receivable reserve policy in light of our tenant base and general and local economic conditions . our accounts receivable allowance was $ 5.1 million or 2.9 % of total receivables ( including accrued rent receivable ) as of december 31 , 2020 compared to $ 8.0 million or 4.0 % of total receivables ( including accrued rent receivable ) as of december 31 , 2019. the decrease in the accounts receivable allowance as a percentage of the total receivables is primarily due to the write-off of the accrued rent receivable for certain retail tenants where revenue is now being recognized on a cash basis due to collectability concerns arising from the economic conditions resulting from the covid-19 pandemic . 29 if economic conditions deteriorate , including as a result of the ongoing covid-19 pandemic , we may experience increases in past due accounts , defaults , lower occupancy and reduced effective rents . this condition would negatively affect our future net income and cash flows and could have a material adverse effect on our financial condition . development risk : development projects are subject to a variety of risks , including construction delays , construction cost overruns , building moratoriums , inability to obtain financing on favorable terms , inability to lease space at projected rates , inability to enter into construction , development and other agreements on favorable terms , and unexpected environmental and other hazards . during the second quarter of 2020 , certain development projects were impacted by building moratoriums imposed by local governments as a result of the covid-19 pandemic . these moratoriums have since been lifted in all geographies in which we have active development projects , but could be reinstated in the event of a significant increase in covid-19 cases . the construction delays did not materially impact the development projects . story_separator_special_tag depreciation and amortization depreciation and amortization expense decreased by $ 21.7 million from 2019 to 2020 primarily driven by the following : $ 12.4 million decrease related to the 2019 and 2020 dispositions ; $ 7.7 million decrease related to our same store property portfolio , largely due to the completion of amortization of acquired in-place lease intangibles and the write-off of lease intangibles in connection with an early lease termination at 1676 international drive in our metropolitan washington , d.c. segment in 2019 ; and $ 1.5 million decrease related to our development/redevelopment properties primarily related to a property placed into redevelopment in our philadelphia cbd segment . general and administrative expenses general and administrative expenses across our total portfolio decreased by $ 1.9 million from 2019 to 2020 , primarily related to a $ 0.8 million decrease in payroll , bonus , stock compensation expense , and related benefits , $ 0.4 million decrease in travel and entertainment/meals , and $ 0.4 million decrease in professional fees . net gain on disposition of real estate the $ 289.5 million gain on disposition of real estate for 2020 primarily resulted from the following sales transactions : $ 271.9 million related to the sale of a 30 % preferred equity interest in one commerce square and two commerce square , which resulted in deconsolidation of the properties and recognition of our investment in the properties at fair value ; $ 15.2 million related to the sale of a 60 % equity interest in a portfolio of twelve suburban office properties located in suburban pennsylvania and maryland , containing an aggregate of 1.1 million square feet ( `` mid-atlantic office portf olio `` ) , which resulted in deconsolidation of the properties and recognition of our investment in the properties at fair value ; and $ 2.3 million related to the disposition of 52 east swedesford road , an office property in our pennsylvania suburbs segment . the $ 0.4 million gain on disposition of real estate for 2019 relates to the disposition of the office property at 1900 gallows road in vienna , virginia . net gain on sale of undepreciated real estate the gain of $ 0.2 million recognized during 2020 primarily resulted from the sale of a land parcel in horsham , pennsylvania . the gain of $ 2.0 million recognized during 2019 relates to the sale of 9 presidential boulevard and from additional consideration received during 2019 related to the libertyview disposition , which occurred in 2015 . 35 interest expense interest expense decreased $ 7.6 million from 2019 to 2020 primarily driven by the following : $ 4.2 million decrease due to deconsolidation of one commerce square and two commerce square and the associated mortgage loans on july 21 , 2020 ; $ 2.0 million reduction to prior period accretions of interest expense on account of a contingent payment to an unaffiliated third party , a portion of which contingent payment ceased to be probable in the third quarter due to the purchase of the two logan square first mortgage ; $ 1.5 million decrease due to an increase in capitalized interest for 2020 compared to 2019 . $ 0.3 million additional decrease in interest expense due to the acquisition of the first mortgage on two logan square ; and $ 4.5 million decrease primarily related to decreased borrowings on the line of credit and lower interest rates during 2020 compared to 2019. these decreases were offset by a $ 4.9 million increase in interest expense related to our issuance of an additional $ 100.0 million in aggregate principal amount of each of our outstanding 4.100 % guaranteed notes due 2024 and 4.550 % guaranteed notes due 2029 during the fourth quarter of 2019. equity in loss of real estate ventures equity in loss of real estate ventures increased $ 8.7 million from 2019 to 2020 is primarily related to : $ 9.2 million increase associated with our commerce square venture formed on july 21 , 2020 ; $ 1.8 million increase related to depreciation and interest expense being recorded at our 4040 wilson venture due to portions of the project being placed into service during 2020 as leases commenced ; $ 0.5 million increase related to our map venture due to lower revenues from lower occupancy rate during 2020 than 2019 ; and $ 0.3 million increase related to reduced parking income at our 1919 market street venture due to the covid-19 pandemic . these increases were offset by a decrease in equity in loss of real estate ventures of $ 2.8 million at our allstate venture related to a held for use impairment recorded during 2019 , compared to no impairments in 2020. net gain on real estate venture transactions the $ 11.6 million net gain on real estate venture transactions during 2019 primarily relates to the following : $ 8.0 million related to the disposition of the pjp ii , pjp vi and pjp vii ventures ; $ 2.2 million related to the transfer of 3130 fairview to the mortgage lender in full satisfaction of the outstanding mortgage loan by the bdn ai venture ; and $ 1.3 million related to proceeds received from the third-party owner of an adjacent property for the right to construct an “ above-grade connection ” with the building owned by the 51 n street venture . net income net income increased by $ 272.8 million from 2019 to 2020 as a result of the factors described above . net income per common share – fully diluted net income per share was $ 1.77 during 2020 as compared to net income per share of $ 0.19 during 2019 as a result of the factors described above . 36 liquidity and capital resources general our principal liquidity funding needs for the next twelve months are as follows : normal recurring expenses ; capital expenditures , including capital and tenant improvements and leasing costs ; debt service and principal repayment

cash flows the following discussion of our cash flows is based on the consolidated statements of cash flows and is not meant to be a comprehensive discussion of the changes in our cash flows for the years presented . as of december 31 , 2020 and 2019 , we maintained cash and cash equivalents and restricted cash of $ 47.1 million and $ 91.2 million , respectively . the following are the changes in cash flow from our activities for the years ended december 31 , 2020 and 2019 ( in thousands ) : replace_table_token_8_th our principal source of cash flows is from the operation of our properties . our properties provide a relatively consistent stream of cash flows that provide us with the resources to fund operating expenses , debt service and quarterly dividends . cash is used in investing activities to fund acquisitions , development , or redevelopment projects and recurring and nonrecurring capital expenditures . we selectively invest in new projects that enable us to take advantage of our development , leasing , financing , and property management skills and invest in existing buildings that meet our investment criteria . during the year ended december 31 , 2020 , when compared to the year ended december 31 , 2019 , the change in investing cash flows was due to the following activities ( in thousands ) : ( decrease ) increase acquisitions of real estate $ ( 39,769 ) capital expenditures and capitalized interest 38,046 leasing costs/acquisition deposits 4,795 joint venture investments ( 10,196 ) distributions from joint ventures ( 26,905 ) proceeds from the sale of properties 236,319 debt and preferred equity and other investments ( 53,341 ) increase in net cash provided by investing activities $ 148,949 39 we generally fund our investment activity through the sale of real estate , property-level financing , credit facilities , senior unsecured notes , and construction loans . from time to time , we may issue common or preferred shares of beneficial interest , or the operating partnership may issue common or preferred units of limited partnership interest .


 Write a concise suspicious activity report of the following text delimited by triple backquotes. Return your response as a formal report which covers the key points highlighting the location,dates,entity names and account holder information in chronological order of the text.
     ```cash flows the following discussion of our cash flows is based on the consolidated statements of cash flows and is not meant to be a comprehensive discussion of the changes in our cash flows for the years presented . as of december 31 , 2020 and 2019 , we maintained cash and cash equivalents and restricted cash of $ 47.1 million and $ 91.2 million , respectively . the following are the changes in cash flow from our activities for the years ended december 31 , 2020 and 2019 ( in thousands ) : replace_table_token_8_th our principal source of cash flows is from the operation of our properties . our properties provide a relatively consistent stream of cash flows that provide us with the resources to fund operating expenses , debt service and quarterly dividends . cash is used in investing activities to fund acquisitions , development , or redevelopment projects and recurring and nonrecurring capital expenditures . we selectively invest in new projects that enable us to take advantage of our development , leasing , financing , and property management skills and invest in existing buildings that meet our investment criteria . during the year ended december 31 , 2020 , when compared to the year ended december 31 , 2019 , the change in investing cash flows was due to the following activities ( in thousands ) : ( decrease ) increase acquisitions of real estate $ ( 39,769 ) capital expenditures and capitalized interest 38,046 leasing costs/acquisition deposits 4,795 joint venture investments ( 10,196 ) distributions from joint ventures ( 26,905 ) proceeds from the sale of properties 236,319 debt and preferred equity and other investments ( 53,341 ) increase in net cash provided by investing activities $ 148,949 39 we generally fund our investment activity through the sale of real estate , property-level financing , credit facilities , senior unsecured notes , and construction loans . from time to time , we may issue common or preferred shares of beneficial interest , or the operating partnership may issue common or preferred units of limited partnership interest .
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 Suspicious Activity Report : we are closely monitoring the impact of the covid-19 pandemic on all aspects of our business , including how it is impacting our tenants , employees , and business partners . adverse changes in economic conditions , including the ongoing effects of the global covid-19 pandemic , could result in a reduction of the availability of financing and potentially in higher borrowing costs . vacancy rates may increase , and rental rates and rent collection rates may decline , beyond 2020 as the current economic climate may negatively impact tenants . overall economic conditions , including but not limited to higher unemployment and deteriorating financial and credit markets , could have a dampening effect on the fundamentals of our business , including increases in past due accounts , tenant defaults , lower occupancy and reduced effective rents . the ongoing covid-19 pandemic has significantly slowed global economic activity , caused significant volatility in financial markets , and resulted in unprecedented job losses . in addition , the government responses to control the pandemic are creating disruption in the global economy and supply chains and adversely impacting many industries , including owners and developers of office and mixed-use building . these adverse conditions have impacted our net income and cash flows and could have a material adverse effect on our financial condition . we believe that the quality of our assets and the strength of our balance sheet will enable us to raise debt capital , if necessary , in various forms and from different sources , including through secured or unsecured loans from banks , pension funds and life insurance companies . however , there can be no assurance that we will be able to borrow funds on terms that are economically attractive or at all . we continue to seek revenue growth throughout our portfolio by increasing occupancy and rental rates . occupancy at our core properties at december 31 , 2020 was 91.9 % compared to 93.0 % at december 31 , 2019 . 28 the table below summarizes selected operating and leasing statistics of our wholly owned operating properties for the years ended december 31 , 2020 and 2019 : replace_table_token_5_th ( 1 ) does not include properties under development , redevelopment , held for sale , or sold . ( 2 ) includes leasing related to completed developments and redevelopments , as well as sold properties . ( 3 ) calculated as percentage of total square feet . ( 4 ) includes base rent plus reimbursement for operating expenses and real estate taxes . ( 5 ) calculated on a weighted average basis . in seeking to increase revenue through our operating , financing , and investment activities , we also seek to minimize operating risks , including ( i ) tenant rollover risk , ( ii ) tenant credit risk and ( iii ) development risk . tenant rollover risk : we are subject to the risk that tenant leases , upon expiration , will not be renewed , that space may not be relet , or that the terms of renewal or reletting ( including the cost of renovations ) may be less favorable to us than the current lease terms . leases that accounted for approximately 7.1 % of our aggregate final annualized base rents as of december 31 , 2020 ( representing approximately 9.5 % of the net rentable square feet of the properties ) are scheduled to expire without penalty in 2021. we maintain an active dialogue with our tenants in an effort to maximize lease renewals . if we are unable to renew leases or relet space under expiring leases , at anticipated rental rates , or if tenants terminate their leases early , our results of operations and cash flow would be adversely impacted . tenant credit risk : in the event of a tenant default , we may experience delays in enforcing our rights as a landlord and may incur substantial costs in protecting our investment . our management regularly evaluates our accounts receivable reserve policy in light of our tenant base and general and local economic conditions . our accounts receivable allowance was $ 5.1 million or 2.9 % of total receivables ( including accrued rent receivable ) as of december 31 , 2020 compared to $ 8.0 million or 4.0 % of total receivables ( including accrued rent receivable ) as of december 31 , 2019. the decrease in the accounts receivable allowance as a percentage of the total receivables is primarily due to the write-off of the accrued rent receivable for certain retail tenants where revenue is now being recognized on a cash basis due to collectability concerns arising from the economic conditions resulting from the covid-19 pandemic . 29 if economic conditions deteriorate , including as a result of the ongoing covid-19 pandemic , we may experience increases in past due accounts , defaults , lower occupancy and reduced effective rents . this condition would negatively affect our future net income and cash flows and could have a material adverse effect on our financial condition . development risk : development projects are subject to a variety of risks , including construction delays , construction cost overruns , building moratoriums , inability to obtain financing on favorable terms , inability to lease space at projected rates , inability to enter into construction , development and other agreements on favorable terms , and unexpected environmental and other hazards . during the second quarter of 2020 , certain development projects were impacted by building moratoriums imposed by local governments as a result of the covid-19 pandemic . these moratoriums have since been lifted in all geographies in which we have active development projects , but could be reinstated in the event of a significant increase in covid-19 cases . the construction delays did not materially impact the development projects . story_separator_special_tag depreciation and amortization depreciation and amortization expense decreased by $ 21.7 million from 2019 to 2020 primarily driven by the following : $ 12.4 million decrease related to the 2019 and 2020 dispositions ; $ 7.7 million decrease related to our same store property portfolio , largely due to the completion of amortization of acquired in-place lease intangibles and the write-off of lease intangibles in connection with an early lease termination at 1676 international drive in our metropolitan washington , d.c. segment in 2019 ; and $ 1.5 million decrease related to our development/redevelopment properties primarily related to a property placed into redevelopment in our philadelphia cbd segment . general and administrative expenses general and administrative expenses across our total portfolio decreased by $ 1.9 million from 2019 to 2020 , primarily related to a $ 0.8 million decrease in payroll , bonus , stock compensation expense , and related benefits , $ 0.4 million decrease in travel and entertainment/meals , and $ 0.4 million decrease in professional fees . net gain on disposition of real estate the $ 289.5 million gain on disposition of real estate for 2020 primarily resulted from the following sales transactions : $ 271.9 million related to the sale of a 30 % preferred equity interest in one commerce square and two commerce square , which resulted in deconsolidation of the properties and recognition of our investment in the properties at fair value ; $ 15.2 million related to the sale of a 60 % equity interest in a portfolio of twelve suburban office properties located in suburban pennsylvania and maryland , containing an aggregate of 1.1 million square feet ( `` mid-atlantic office portf olio `` ) , which resulted in deconsolidation of the properties and recognition of our investment in the properties at fair value ; and $ 2.3 million related to the disposition of 52 east swedesford road , an office property in our pennsylvania suburbs segment . the $ 0.4 million gain on disposition of real estate for 2019 relates to the disposition of the office property at 1900 gallows road in vienna , virginia . net gain on sale of undepreciated real estate the gain of $ 0.2 million recognized during 2020 primarily resulted from the sale of a land parcel in horsham , pennsylvania . the gain of $ 2.0 million recognized during 2019 relates to the sale of 9 presidential boulevard and from additional consideration received during 2019 related to the libertyview disposition , which occurred in 2015 . 35 interest expense interest expense decreased $ 7.6 million from 2019 to 2020 primarily driven by the following : $ 4.2 million decrease due to deconsolidation of one commerce square and two commerce square and the associated mortgage loans on july 21 , 2020 ; $ 2.0 million reduction to prior period accretions of interest expense on account of a contingent payment to an unaffiliated third party , a portion of which contingent payment ceased to be probable in the third quarter due to the purchase of the two logan square first mortgage ; $ 1.5 million decrease due to an increase in capitalized interest for 2020 compared to 2019 . $ 0.3 million additional decrease in interest expense due to the acquisition of the first mortgage on two logan square ; and $ 4.5 million decrease primarily related to decreased borrowings on the line of credit and lower interest rates during 2020 compared to 2019. these decreases were offset by a $ 4.9 million increase in interest expense related to our issuance of an additional $ 100.0 million in aggregate principal amount of each of our outstanding 4.100 % guaranteed notes due 2024 and 4.550 % guaranteed notes due 2029 during the fourth quarter of 2019. equity in loss of real estate ventures equity in loss of real estate ventures increased $ 8.7 million from 2019 to 2020 is primarily related to : $ 9.2 million increase associated with our commerce square venture formed on july 21 , 2020 ; $ 1.8 million increase related to depreciation and interest expense being recorded at our 4040 wilson venture due to portions of the project being placed into service during 2020 as leases commenced ; $ 0.5 million increase related to our map venture due to lower revenues from lower occupancy rate during 2020 than 2019 ; and $ 0.3 million increase related to reduced parking income at our 1919 market street venture due to the covid-19 pandemic . these increases were offset by a decrease in equity in loss of real estate ventures of $ 2.8 million at our allstate venture related to a held for use impairment recorded during 2019 , compared to no impairments in 2020. net gain on real estate venture transactions the $ 11.6 million net gain on real estate venture transactions during 2019 primarily relates to the following : $ 8.0 million related to the disposition of the pjp ii , pjp vi and pjp vii ventures ; $ 2.2 million related to the transfer of 3130 fairview to the mortgage lender in full satisfaction of the outstanding mortgage loan by the bdn ai venture ; and $ 1.3 million related to proceeds received from the third-party owner of an adjacent property for the right to construct an “ above-grade connection ” with the building owned by the 51 n street venture . net income net income increased by $ 272.8 million from 2019 to 2020 as a result of the factors described above . net income per common share – fully diluted net income per share was $ 1.77 during 2020 as compared to net income per share of $ 0.19 during 2019 as a result of the factors described above . 36 liquidity and capital resources general our principal liquidity funding needs for the next twelve months are as follows : normal recurring expenses ; capital expenditures , including capital and tenant improvements and leasing costs ; debt service and principal repayment

