13. SEGMENT FINANCIAL INFORMATION Our four reportable segments are office, retail, multi-family and industrial. Factors used to determine our reportable segments include the physical and economic characteristics of our properties and the related operating activities. Our chief operating decision makers rely on net operating income, among other factors, to make decisions about allocating resources and assessing segment performance. Net operating income is the key performance metric that captures the unique operating characteristics of each segment. Items that are not directly assignable to a segment, such as certain corporate items, are not allocated but reflected as reconciling items. The following table reflects our total assets by business segment as of September 30, 2020 and December 31, 2019: As of (in thousands) September 30, 2020 December 31, 2019 Assets: Office properties $ 461,993 $ 458,583 Retail properties 689,395 652,707 Multi-family properties 287,035 293,498 Industrial properties 338,924 207,844 Corporate 159,399 165,633 Total assets $ 1,936,746 $ 1,778,265 The following table sets forth the financial results by segment for the three and nine months ended September 30, 2020 and 2019: (in thousands) Office Retail Multi-family Industrial Consolidated For the Three Months Ended September 30, 2020 Rental revenues $ 16,237 $ 17,310 $ 4,351 $ 6,231 $ 44,129 Rental expenses (7,748) (4,535) (2,282) (1,316) (15,881) Net operating income $ 8,489 $ 12,775 $ 2,069 $ 4,915 $ 28,248 Real estate-related depreciation and amortization $ 4,851 $ 5,309 $ 2,234 $ 3,255 $ 15,649 For the Three Months Ended September 30, 2019 Rental revenues $ 20,470 $ 17,422 $ 2,945 $ 3,358 $ 44,195 Rental expenses (8,916) (4,323) (1,441) (680) (15,360) Net operating income $ 11,554 $ 13,099 $ 1,504 $ 2,678 $ 28,835 Real estate-related depreciation and amortization $ 6,281 $ 4,547 $ 2,008 $ 1,637 $ 14,473 For the Nine Months Ended September 30, 2020 Rental revenues $ 48,988 $ 53,053 $ 14,591 $ 16,363 $ 132,995 Rental expenses (23,061) (12,561) (6,638) (3,532) (45,792) Net operating income $ 25,927 $ 40,492 $ 7,953 $ 12,831 $ 87,203 Real estate-related depreciation and amortization $ 14,676 $ 14,867 $ 6,560 $ 8,455 $ 44,558 For the Nine Months Ended September 30, 2019 Rental revenues $ 74,383 $ 52,938 $ 2,945 $ 9,385 $ 139,651 Rental expenses (29,174) (12,986) (1,441) (2,044) (45,645) Net operating income $ 45,209 $ 39,952 $ 1,504 $ 7,341 $ 94,006 Real estate-related depreciation and amortization $ 21,268 $ 15,606 $ 2,008 $ 4,579 $ 43,461 We consider net operating income to be an appropriate supplemental performance measure and believe net operating income provides useful information to our investors regarding our financial condition and results of operations because net operating income reflects the operating performance of our properties and excludes certain items that are not considered to be controllable in connection with the management of the properties, such as real estate-related depreciation and amortization, general and administrative expenses, advisory fees, impairment charges, interest expense, gains on sale of properties, other income and expense, gains and losses on the extinguishment of debt and noncontrolling interests. However, net operating income should not be viewed as an alternative measure of our financial performance since it excludes such items, which could materially impact our results of operations. Further, our net operating income may not be comparable to that of other real estate companies, as they may use different methodologies for calculating net operating income. Therefore, we believe net income, as defined by GAAP, to be the most appropriate measure to evaluate our overall financial performance. The following table is a reconciliation of our reported net income (loss) attributable to common stockholders to our net operating income for the three and nine months ended September 30, 2020 and 2019: For the Three Months Ended For the Nine Months Ended September 30, September 30, (in thousands) 2020 2019 2020 2019 Net (loss) income attributable to common stockholders $ (10,830) $ 7,291 $ (19,827) $ 88,292 Debt-related income (981) (35) (1,181) (193) Real estate-related depreciation and amortization 15,649 14,473 44,558 43,461 General and administrative expenses 2,217 2,181 6,611 6,325 Advisory fees, related party 5,543 3,523 16,009 9,887 Litigation expense 2,500  2,500  Impairment of real estate property  113  113 Other income (262) (131) (619) (156) Interest expense 15,290 11,764 42,930 37,074 Gain on sale of real estate property  (10,890) (2,192) (96,530) Gain on extinguishment of debt and financing commitments, net    (1,002) Net loss attributable to redeemable noncontrolling interests (39)  (71)  Net (loss) income attributable to noncontrolling interests (839) 546 (1,515) 6,735 Net operating income $ 28,248 $ 28,835 $ 87,203 $ 94,006