11. REPORTABLE SEGMENTS GAAP guidance requires that segment disclosures present the measure(s) used by the Chief Operating Decision Maker to decide how to allocate resources and for purposes of assessing such segments performance. The Operating Partnership has the same Chief Operating Decision Maker as that of its parent, the General Partner. The Chief Operating Decision Maker consists of several members of UDRs executive management team who use several generally accepted industry financial measures to assess the performance of the business for our reportable operating segments. The Operating Partnership owns and operates multifamily apartment communities throughout the United States that generate rental and other property related income through the leasing of apartment homes to a diverse base of tenants. The primary financial measures of the Operating Partnerships apartment communities are rental income and net operating income (NOI), and are included in the Chief Operating Decision Makers assessment of the Operating Partnerships performance on a consolidated basis. Rental income represents gross market rent less adjustments for concessions, vacancy loss and bad debt. NOI is defined as total revenues less direct property operating expenses. Rental expenses include real estate taxes, insurance, personnel, utilities, repairs and maintenance, administrative and marketing. Excluded from NOI are property management costs, which are the Operating Partnerships allocable share of costs incurred by the General Partner for shared services of corporate level property management employees and related support functions and costs. The Chief Operating Decision Maker of the General Partner utilizes NOI as the key measure of segment profit or loss. The Operating Partnerships two reportable segments are Same-Store Communities and Non-Mature Communities/Other : ? Same-Store Communities represent those communities acquired, developed, and stabilized prior to January 1, 2017 and held as of December 31, 2018. A comparison of operating results from the prior year is meaningful as these communities were owned and had stabilized occupancy and operating expenses as of the beginning of the prior year, there is no plan to conduct substantial redevelopment activities, and the community is not held for disposition within the current year. A community is considered to have stabilized occupancy once it achieves 90% occupancy for at least three consecutive months. ? Non-Mature Communities/Other represent those communities that do not meet the criteria to be included in Same-Store Communities , including, but not limited to, recently acquired, developed and redeveloped communities, and the non-apartment components of mixed use properties. Management of the General Partner evaluates the performance of each of the Operating Partnerships apartment communities on a Same-Store Community and Non-Mature Community/Other basis, as well as individually and geographically. This is consistent with the aggregation criteria under GAAP as each of our apartment communities generally has similar economic characteristics, facilities, services, and tenants. Therefore, the Operating Partnerships reportable segments have been aggregated by geography in a manner identical to that which is provided to the Chief Operating Decision Maker. All revenues are from external customers and no single tenant or related group of tenants contributed 10% or more of the Operating Partnerships total revenues during the years ended December 31, 2018, 2017, and 2016. The following table details rental income and NOI for the Operating Partnerships reportable segments for the years ended December 31, 2018, 2017, and 2016, and reconciles NOI to Net income/(loss) attributable to OP unitholders on the Consolidated Statements of Operations (dollars in thousands) : Year Ended December 31, 2018 2017 2016 Reportable apartment home segment rental income Same-Store Communities West Region $ 246,047 $ 235,022 $ 223,539 Mid-Atlantic Region 60,389 59,006 57,563 Northeast Region 54,749 54,530 53,036 Southeast Region 51,896 49,586 47,792 Non-Mature Communities/Other 18,839 21,233 22,485 Total segment and consolidated rental income $ 431,920 419,377 $ 404,415 Reportable apartment home segment NOI Same-Store Communities West Region $ 187,664 $ 177,229 $ 168,762 Mid-Atlantic Region 41,642 40,292 38,711 Northeast Region 39,456 40,524 40,704 Southeast Region 35,948 34,182 32,519 Non-Mature Communities/Other 12,670 14,614 16,425 Total segment and consolidated NOI 317,380 306,841 297,121 Reconciling items: Property management (11,878) (11,533) (11,122) Other operating expenses (8,864) (6,833) (6,059) Real estate depreciation and amortization (143,481) (152,473) (147,074) General and administrative (16,889) (17,875) (18,808) Casualty-related (charges)/recoveries, net (951) (1,922) (484) Income/(loss) from unconsolidated entities 43,496 (19,256) (37,425) Interest expense (22,835) (30,366) (30,067) Gain/(loss) on sale of real estate owned 75,507 41,272 33,180 Net (income)/loss attributable to noncontrolling interests (1,722) (1,548) (1,444) Net income/(loss) attributable to OP unitholders $ 229,763 $ 106,307 $ 77,818 The following table details the assets of the Operating Partnerships reportable segments as of December 31, 2018 and 2017 (dollars in thousands) : December 31, December 31, 2018 2017 Reportable apartment home segment assets Same-Store Communities West Region $ 1,981,007 $ 1,955,962 Mid-Atlantic Region 663,083 655,850 Northeast Region 681,953 677,767 Southeast Region 340,722 334,811 Non-Mature Communities/Other 145,220 192,566 Total segment assets 3,811,985 3,816,956 Accumulated depreciation (1,658,161) (1,543,652) Total segment assets - net book value 2,153,824 2,273,304 Reconciling items: Cash and cash equivalents 125 293 Restricted cash 13,563 12,579 Investment in unconsolidated entities 103,026 76,907 Other assets 34,052 32,490 Total consolidated assets $ 2,304,590 $ 2,395,573 Capital expenditures related to the Operating Partnerships Same-Store Communities totaled $41.0 million, $41.8 million and $41.5 million for the years ended December 31, 2018, 2017, and 2016, respectively. Capital expenditures related to the Operating Partnerships Non-Mature Communities/Other totaled $0.9 million, $1.8 million, and $2.6 million for the years ended December 31, 2018, 2017, and 2016, respectively. Markets included in the above geographic segments are as follows: i. West Region  Orange County, San Francisco, Seattle, Los Angeles, Monterey Peninsula, Other Southern California and Portland ii. Mid-Atlantic Region  Metropolitan, D.C. and Baltimore iii. Northeast Region  New York and Boston iv. Southeast Region  Tampa, Nashville and Other Florida v. Southwest Region  Denver