Segment Reporting Management reviews the performance of individual properties and aggregates individual properties based on operating criteria into two reportable segmentscommercial real estate investments in data centers and healthcare, and makes operating decisions based on these two reportable segments. The Companys commercial real estate investments in data centers and healthcare are based on certain underwriting assumptions and operating criteria, which are different for data centers and healthcare. The Company evaluates performance based on net operating income of the individual properties in each segment. Net operating income, a non-GAAP financial measure, is defined as rental revenue, less rental expenses, which excludes depreciation and amortization, general and administrative expenses, asset management fees and interest and other expense, net. The Company believes that segment net operating income serves as a useful supplement to net income because it allows investors and management to measure unlevered property-level operating results and to compare operating results to the operating results of other real estate companies between periods on a consistent basis. Segment net operating income should not be considered as an alternative to net income determined in accordance with GAAP as an indicator of financial performance, and accordingly, the Company believes that in order to facilitate a clear understanding of the consolidated historical operating results, segment net operating income should be examined in conjunction with net income as presented in the accompanying condensed consolidated financial statements and data included elsewhere in this Quarterly Report on Form 10-Q . Non-segment assets primarily consist of corporate assets, including cash and cash equivalents, real estate and escrow deposits, deferred financing costs attributable to the revolving line of credit portion of the Company's credit facility and other assets not attributable to individual properties. Summary information for the reportable segments during the three and six months ended June 30, 2019 and 2018 , is as follows (amounts in thousands): Data Center Healthcare Three Months Ended June 30, 2019 Revenue: Rental revenue $ 27,838 $ 19,099 $ 46,937 Expenses: Rental expenses (8,137 ) (2,005 ) (10,142 ) Segment net operating income $ 19,701 $ 17,094 36,795 Expenses: General and administrative expenses (1,535 ) Asset management fees (3,493 ) Depreciation and amortization (15,610 ) Income from operations 16,157 Interest and other expense, net (9,893 ) Net income attributable to common stockholders $ 6,264 Data Center Healthcare Three Months Ended June 30, 2018 Revenue: Rental revenue $ 25,879 $ 18,071 $ 43,950 Expenses: Rental expenses (7,200 ) (2,502 ) (9,702 ) Segment net operating income $ 18,679 $ 15,569 34,248 Expenses: General and administrative expenses (1,339 ) Asset management fees (3,233 ) Depreciation and amortization (14,282 ) Income from operations 15,394 Interest and other expense, net (8,208 ) Net income attributable to common stockholders $ 7,186 Data Centers Healthcare Six Months Ended June 30, 2019 Revenue: Rental revenue $ 54,515 $ 38,889 $ 93,404 Expenses: Rental expenses (15,102 ) (4,168 ) (19,270 ) Segment net operating income $ 39,413 $ 34,721 74,134 Expenses: General and administrative expenses (2,938 ) Asset management fees (6,987 ) Depreciation and amortization (33,856 ) Income from operations 30,353 Interest and other expense, net (19,728 ) Net income attributable to common stockholders $ 10,625 Data Centers Healthcare Six Months Ended June 30, 2018 Revenue: Rental revenue $ 49,600 $ 35,645 $ 85,245 Expenses: Rental expenses (13,137 ) (4,855 ) (17,992 ) Segment net operating income $ 36,463 $ 30,790 67,253 Expenses: General and administrative expenses (2,282 ) Asset management fees (6,332 ) Depreciation and amortization (27,999 ) Income from operations 30,640 Interest and other expense, net (15,950 ) Net income attributable to common stockholders $ 14,690 There were no intersegment sales or transfers during the three and six months ended June 30, 2019 and 2018 . Assets by each reportable segment as of June 30, 2019 and December 31, 2018 are as follows (amounts in thousands): June 30, 2019 December 31, 2018 Assets by segment: Data centers $ 997,431 $ 1,001,357 Healthcare 883,472 900,114 All other 60,510 62,358 Total assets $ 1,941,413 $ 1,963,829 Capital additions and acquisitions by reportable segments for the six months ended June 30, 2019 and 2018 are as follows (amounts in thousands): Six Months Ended June 30, 2019 2018 Capital additions and acquisitions by segment: Data centers $ 6,019 $ 103,865 Healthcare 150 35,096 Total capital additions and acquisitions $ 6,169 $ 138,961