Basis of Presentation and Principles of Consolidation and Significant Accounting Policies | 1. Basis of Presentation and Principles of Consolidation and Significant Accounting Policies Unless the context otherwise requires, all references to the "Company" refer collectively to Mid-America Apartment Communities, Inc., together with its consolidated subsidiaries, including Mid-America Apartments, L.P. Unless the context otherwise requires, all references to "MAA" refer only to Mid-America Apartment Communities, Inc., and not any of its consolidated subsidiaries. Unless the context otherwise requires, the references to the "Operating Partnership" or "MAALP" refer to Mid-America Apartments, L.P. together with its consolidated subsidiaries. "Common stock" refers to the common stock of MAA and, unless the context otherwise requires, "shareholders" refers to the holders of shares of MAA’s common stock. The common units of limited partnership interests in the Operating Partnership are referred to as "OP Units," and the holders of the OP Units are referred to as "common unitholders". As of September 30, 2019, MAA owned 114,065,859 OP Units (or 96.6% of the total number of OP Units). MAA conducts substantially all of its business and holds substantially all of its assets, directly or indirectly, through the Operating Partnership, and by virtue of its ownership of the OP Units and being the Operating Partnership's sole general partner, MAA has the ability to control all of the day-to-day operations of the Operating Partnership. Management believes combining the notes to the condensed consolidated financial statements of MAA and the Operating Partnership results in the following benefits: • enhances readers' understanding of MAA and the Operating Partnership by enabling the reader to view the business as a whole in the same manner that management views and operates the business; • eliminates duplicative disclosure and provides a more streamlined and readable presentation since a substantial portion of the disclosure applies to both MAA and the Operating Partnership; and • creates time and cost efficiencies through the preparation of one combined set of notes instead of two separate sets. MAA is a multifamily focused, self-administered and self-managed real estate investment trust, or REIT. Management operates MAA and the Operating Partnership as one business. The management of the Company is comprised of individuals who are officers of MAA and employees of the Operating Partnership. Management believes it is important to understand the few differences between MAA and the Operating Partnership in the context of how MAA and the Operating Partnership operate as a consolidated company. MAA and the Operating Partnership are structured as an umbrella partnership REIT, or UPREIT. MAA's interest in the Operating Partnership entitles MAA to share in cash distributions from, and in the profits and losses of, the Operating Partnership in proportion to MAA's percentage interest therein and entitles MAA to vote on substantially all matters requiring a vote of the partners. MAA's only material asset is its ownership of limited partnership interests in the Operating Partnership (other than cash held by MAA from time to time); therefore, MAA's primary function is acting as the sole general partner of the Operating Partnership, issuing public equity from time to time and guaranteeing certain debt of the Operating Partnership. The Operating Partnership holds, directly or indirectly, all of the Company's real estate assets. Except for net proceeds from public equity issuances by MAA, which are contributed to the Operating Partnership in exchange for limited partnership interests, the Operating Partnership generates the capital required by the business through the Operating Partnership's operations, direct or indirect incurrence of indebtedness and issuance of OP Units. The presentations of MAA's shareholders' equity and the Operating Partnership's capital are the principal areas of difference between the condensed consolidated financial statements of MAA and those of the Operating Partnership. MAA's shareholders' equity may include shares of preferred stock, shares of common stock, additional paid-in capital, cumulative earnings, cumulative distributions, noncontrolling interests, treasury shares, accumulated other comprehensive income and redeemable common stock. The Operating Partnership's capital may include common capital and preferred capital of the general partner (MAA), limited partners' common capital and preferred capital, noncontrolling interests, accumulated other comprehensive income and redeemable common units. Holders of OP Units (other than MAA) may require the Operating Partnership to redeem their OP Units from time to time, in which case the Operating Partnership may, at its option, pay the redemption price either in cash (in an amount per OP Unit equal, in general, to the average closing price of MAA's common stock on the New York Stock Exchange, or NYSE, over a specified period prior to the redemption date) or by delivering one share of MAA's common stock (subject to adjustment under specified circumstances) for each OP Unit so redeemed. Organization of Mid-America Apartment Communities, Inc. The Company owns, operates, acquires and selectively develops apartment communities primarily located in the Southeast, Southwest and Mid-Atlantic regions of the United States. As of September 30, 2019, the Company owned and operated 303 apartment communities through the Operating Partnership and its subsidiaries and had an ownership interest in one apartment community through an unconsolidated real estate joint venture. As of September 30, 2019, the Company had six development communities under construction totaling 1,686 apartment units. Total expected costs for these six development projects are $389.5 million, of which $106.7 million had been incurred through September 30, 2019. The Company expects to complete one development in the last quarter of 2019, one development in the first half of 2020, one developmen t in the second half of 2020, one development in the first half of 2021 , and two developments in the second half of 2021 . Thirty-one of the Company's apartment communities include retail components with approximately 630,000 square feet of gross leasable space. The Company also has four commercial properties with approximately 260,000 square feet of combined gross leasable area. The Company’s apartment communities and commercial properties are located across 17 states and the District of Columbia. Basis of Presentation and Principles of Consolidation The accompanying condensed consolidated financial statements have been prepared by the Company's management in accordance with United States generally accepted accounting principles, or GAAP, and applicable rules and regulations of the Securities and Exchange Commission, or the SEC. The condensed consolidated financial statements of MAA presented herein include the accounts of MAA, the Operating Partnership and all other subsidiaries in which MAA has a controlling financial interest. MAA owns, directly or indirectly, approximately 80% to 100% of all consolidated subsidiaries, including the Operating Partnership. The condensed consolidated financial statements of MAALP presented herein include the accounts of MAALP and all other subsidiaries in which MAALP has a controlling financial interest. MAALP owns, directly or indirectly, 80% to 100% of all consolidated subsidiaries. In management's opinion, all adjustments necessary for a fair presentation of the condensed consolidated financial statements have been included, and all such adjustments were of a normal recurring nature. All significant intercompany accounts and transactions have been eliminated in consolidation. The Company invests in entities which may qualify as variable interest entities, or VIEs, and MAALP is considered a VIE. A VIE is a legal entity in which the equity investors lack sufficient equity at risk for the entity to finance its activities without additional subordinated financial support or, as a group, the holders of the equity investment at risk lack the power to direct the activities of a legal entity as well as the obligation to absorb its expected losses or the right to receive its expected residual returns. MAALP is classified as a VIE, since the limited partners lack substantive kick-out rights and substantive participating rights. The Company consolidates all VIEs for which it is the primary beneficiary and uses the equity method to account for investments that qualify as VIEs but for which it is not the primary beneficiary. In determining whether the Company is the primary beneficiary of a VIE, management considers both qualitative and quantitative factors, including but not limited to, those activities that most significantly impact the VIE's economic performance and which party controls such activities. The Company uses the equity method of accounting for its investments in entities for which the Company exercises significant influence, but does not have the ability to exercise control. The factors considered in determining whether the Company has the ability to exercise control include ownership of voting interests and participatory rights of investors (see "Investments in Unconsolidated Affiliates" below). Changes in Presentation In an effort to simplify the Company's presentation of cash flows from financing activities within the condensed consolidated statements of cash flows, the Company combined "Repurchase of common stock"; "Debt prepayment and extinguishment costs"; "Proceeds from issuances of common shares"; and "Exercise of stock options" into one line, "Net change in other financing activities" within the cash flows from financing activities section. No presentation changes were made to the cash flows from operating or investing activities sections of the condensed consolidated statements of cash flows. Prior year amounts have been changed to conform to the Company's current year presentation. These changes in presentation had no effect on the Company's ending cash, cash equivalents and restricted cash balances and did not impact the classification of cash flows between operating, investing and financing activities. Noncontrolling Interests As of September 30, 2019, the Company had two types of noncontrolling interests with respect to its consolidated subsidiaries, (1) noncontrolling interests related to the common unitholders of its Operating Partnership (see below) and (2) noncontrolling interests related to its consolidated real estate entities (see "Investment in Consolidated Real Estate Entities" below). The noncontrolling interests in the accompanying condensed consolidated financial statements relating to the limited partnership interests in the Operating Partnership are owned by the holders of the Class A OP Units. MAA is the sole general partner of the Operating Partnership and holds all of the outstanding Class B OP Units. Net income (after allocations to preferred ownership interests) is allocated to MAA and the noncontrolling interests based on their respective ownership percentages of the Operating Partnership. Issuance of additional Class A OP Units or Class B OP Units changes the ownership percentage of both the noncontrolling interests and MAA. The issuance of Class B OP Units generally occurs when MAA issues common stock and the issuance proceeds are contributed to the Operating Partnership in exchange for Class B OP Units equal to the number of shares of MAA's common stock issued. At each reporting period, the allocation between total MAA shareholders’ equity and noncontrolling interests is adjusted to account for the change in the respective percentage ownership of the underlying equity of the Operating Partnership. MAA’s Board of Directors established economic rights in respect to each Class A OP Unit that were equivalent to the economic rights in respect to each share of MAA common stock. See Note 9 for additional details. Investments in Unconsolidated Affiliates Through its investment in a limited liability company, or the Apartment LLC, the Company together with an institutional investor indirectly owns one apartment community, Post Massachusetts Avenue, located in Washington, D.C. The Company owned a 35.0% equity interest in the unconsolidated real estate joint venture as of September 30, 2019 and provides property and asset management services to the Apartment LLC for which it earns fees. The joint venture was determined to be a VIE, but the Company is not designated as the primary beneficiary. As a result, the Company accounts for its investment in the Apartment LLC using the equity method of accounting as the Company is able to exert significant influence over the joint venture but does not have a controlling interest. As of September 30, 2019 , the Company's investment in the Apartment LLC totaled $43.8 million . In September 2017, a subsidiary of the Operating Partnership invested in a limited partnership, Real Estate Technology Ventures, L.P. As of September 30, 2019, the Operating Partnership indirectly owned 20.4% of the limited partnership. The limited partnership was determined to be a VIE, but the Company is not designated as the primary beneficiary. As a result, the Company accounts for its investment in the limited partnership using the equity method of accounting as the investment is considered more than minor. As of September 30, 2019, the Company's investment in the limited partnership totaled $12.3 million and is included in "Other assets" in the accompanying Condensed Consolidated Balance Sheets. As of September 30, 2019, the Company was committed until September 2022 to make additional capital contributions totaling $9.0 million if and when called by the general partner of the limited partnership. Investments in Consolidated Real Estate Entities The Company owns a 92.5% equity interest in a consolidated real estate entity that developed, constructed and operates a 359-unit apartment community in Denver, Colorado. The owner of the remaining 7.5% equity interest, a private real estate company, was generally responsible for the development and construction of the community, which was completed during the year ended December 31, 2018. The Company, through the consolidated real estate entity, will continue to operate and manage the apartment community. The consolidated real estate entity was determined to be a VIE with the Company designated as the primary beneficiary. As a result, the accounts of the consolidated real estate entity are consolidated by the Company. As of September 30, 2019, the assets and liabilities of the consolidated real estate entity included buildings and improvements and other, net of accumulated depreciation, of $68.5 million; land of $14.9 million; and accrued expenses and other liabilities of $1.0 million. During the first quarter of 2019, the Company acquired an 80.0% equity interest in a consolidated real estate entity that will develop, construct and operate an apartment community in Phoenix, Arizona. The consolidated real estate entity acquired the land site and initiated development of the apartment community in the first quarter of 2019. The owner of the remaining 20.0% equity interest, a private real estate company, is responsible for the development and construction of the apartment community. The Company will lease-up the property when apartment units are delivered and operate and manage the apartment community upon its completion. The consolidated real estate entity was determined to be a VIE with the Company designated as the primary beneficiary. As a result, the accounts of the consolidated real estate entity are consolidated by the Company. As of September 30, 2019, the assets and liabilities of the consolidated real estate entity included development and capital improvements in process of $14.3 million; land of $9.4 million; and accrued expenses and other liabilities of $2.4 million. Fair Value Measurements The Company applies the guidance in Accounting Standards Codification, or ASC, Topic 820, Fair Value Measurements and Disclosures Level 1 - Quoted prices in active markets for identical assets or liabilities that are accessible at the measurement date. Level 2 - Inputs other than quoted prices that are observable for the asset or liability, either directly or indirectly. Level 3 - Unobservable inputs for the assets or liability. Leases In 2016, the Financial Accounting Standard Board, or FASB, issued Accounting Standard Update, or ASU, 2016-02, Leases Comparative periods presented in this Quarterly Report on Form 10-Q continue to apply guidance in ASC Topic 840, Leases, lease components when certain criteria are met, and instead, allow for those components to be accounted for as a single lease component. Thus, beginning with the effective date of the adoption of the new standard, January 1, 2019, rental revenues and non-lease reimbursable property revenues meet the criteria to be aggregated into a single lease component and are reported in the line item, "Rental revenues", as presented in the disaggregation of the Company's revenues in Note 11. The Company is the lessee under certain ground, office, equipment and other operating leases. Based on its election of the package of practical expedients provided in ASU 2016-02, the Company did not reassess the classification of existing leases with its adoption of ASC Topic 842. The Company’s existing leases as of January 1, 2019 will continue to be accounted for as operating leases; however, if contracts are modified subsequent to the adoption of ASC Topic 842, the Company will be required to reassess the contracts using guidance provided under ASC Topic 842. The Company recognized total right-of-use assets of $54.3 million within "Other assets" and related lease obligations of $33.6 million within "Accrued expenses and other liabilities" on its Condensed Consolidated Balance Sheets for leases in effect as of January 1, 2019. As of September 30, 2019, the balance of total right-of-use assets within “Other assets” was $53.0 million, and the balance of related lease obligations within “Accrued expenses and other liabilities” was $33.0 million. As most leases do not provide a readily determinable implicit rate to discount future minimum lease payments to present value, management estimated the Company's incremental borrowing rate based on information available as of the date of adoption and based on the remaining lease terms as of the date of initial application. Operating leases recognized upon adoption had a weighted-average remaining lease term of approximately 33 years and a weighted-average discount rate of approximately 4.4%. Operating leases as of September 30, 2019 have a weighted-average remaining lease term of approximately 32 years and a weighted-average discount rate of approximately 4.4%. Lease expense for the nine months ended September 30, 2019, recognized under ASC Topic 842, continued to be immaterial for the Company and was recognized in a similar manner as compared to the nine months ended September 30, 2018. Cash paid for amounts included in the measurement of operating lease liabilities during the nine months ended September 30, 2019 was also immaterial. Revenue Recognition The Company primarily leases multifamily residential apartments under operating leases with terms of approximately one year or less, which are recorded as operating leases. Rental revenues are generally due on a monthly basis and are recognized in accordance with ASC Topic 842 using a method that represents a straight-line basis over the term of the lease. In addition, in circumstances where a lease incentive is provided to tenants, the incentive is recognized as a reduction of rental revenues on a straight-line basis over the reasonably assured lease term. Rental revenues represent approximately 93% of the Company's total revenues and include gross rents charged less adjustments for concessions and bad debt. Approximately 6% of the Company's total revenues represent reimbursable property revenues from tenants for utility reimbursements, which are generally recognized and due on a monthly basis as tenants obtain control of the utility service over the term of the lease. The remaining 1% of the Company's total revenues represents other non-lease revenues primarily driven by nonrefundable fees and commissions. With the adoption of ASC Topic 842, rental revenues and non-lease reimbursable property revenues meet the criteria to be aggregated into a single lease component and to be reported in a single line, while non-lease reimbursable property revenues recognized prior to January 1, 2019 will continue to be reported as non-lease revenues and recognized in accordance with ASC Topic 606, Revenue Recognition. Assets Held for Sale In September 2019, one apartment community was classified as held for sale. The criteria for classifying the apartment community as held for sale were met during September 2019; however, the apartment community is not expected to be sold until the fourth quarter of 2019. As a result, the assets and liabilities associated with the apartment community were presented as held for sale in the accompanying Condensed Consolidated Balance Sheets as of September 30, 2019. Subsequent to the September 30, 2019 balance sheet date but prior to the filing date of this Quarterly Report on Form 10-Q, three additional apartment communities met the criteria for classification as held for sale. The sale of these apartment communities is not expected to close until the fourth quarter of 2019. As a result, the assets and liabilities associated with these three apartment communities were presented as held and used in the accompanying Condensed Consolidated Balance Sheets as of September 30, 2019. In October 2019, MAA closed on the disposition of Ridge at Chenal Valley, a 312 unit apartment community located in the Little Rock, Arkansas market, resulting in an expected net gain on sale of approximately $20 million that will be recorded in the fourth quarter of 2019. Recently Issued Accounti ng Pronouncements In June 2016, the FASB issued ASU No. 2016-13, Measurement of Credit Losses on Financial Instruments |