Organization and Summary of Significant Accounting Policies Organization and Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2018
Accounting Policies [Abstract]
Basis of Presentation and Principles of Consolidation	Basis of Presentation and Principles of Consolidation The accompanying 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 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 approximately 92.5% to 100% of all consolidated subsidiaries, including the Operating Partnership. The 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, 92.5% to 100% of all consolidated subsidiaries. In management's opinion, all adjustments necessary for a fair presentation of the 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 "Investment in Unconsolidated Affiliates" below).
Use of Estimates	Use of Estimates Management has made a number of estimates and assumptions relating to the reporting of assets and liabilities, the disclosure of contingent assets and liabilities, and the reported amounts of revenues and expenses to prepare these financial statements and notes in conformity with GAAP. Actual results could differ from those estimates.
Revenue Recognition and Real Estate Sales	Revenue Recognition and Real Estate Sales Gain Recognition The Company primarily leases multifamily residential apartment units under operating leases generally due on a monthly basis with terms of approximately one year or less, which are recorded as operating leases. Rental lease revenues are recognized in accordance with Accounting Standards Codification, or ASC, Topic 840, Leases, 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 lease revenue on a straight-line basis over the reasonably assured lease term. Rental income represents approximately 93% of the Company's total revenues and includes gross market rent less adjustments for concessions, vacancy loss and bad debt. Other non-lease revenues represent the remaining 7% of the Company's total revenues and are primarily driven by utility reimbursement revenues, which are generally recognized and due on a monthly basis as tenants obtain control of the service. The Company's primary sources of reimbursement revenues are from water and cable utility services, which produced revenues of $39.1 million and $29.8 million, respectively, for the year ended December 31, 2018, revenues of $38.3 million and $30.4 million, respectively, for the year ended December 31, 2017 and revenues of $31.1 million and $31.6 million, respectively, for the year ended December 31, 2016. Other non-lease revenues are recognized in accordance with ASC Topic 606, Revenue Recognition, as a result of the Company's January 1, 2018 adoption of Accounting Standards Update, or ASU, 2014-09, Revenue from Contracts with Customers, using the modified retrospective approach. The guidance requires that revenue (outside of the scope of lease revenue accounting rules) is recognized when a customer obtains control of promised goods or services in an amount that reflects the consideration the entity expects to receive in exchange for those goods or services. While ASU 2014-09 requires additional disclosure regarding the nature and timing of the Company's non-lease revenue transactions, which is provided here in Note 1 as well as Note 14, the adoption of the ASU did not have a material impact on the Company's consolidated financial statements or the Company's accounting policies and did not result in an opening adjustment to retained earnings. The Company elected the available practical expedients to the ASU’s requirement for disclosure on remaining performance obligations, which allow an entity to avoid disclosing the amount of the remaining performance obligations for contracts with an original expected duration of less than one year or those that meet the practical expedient in ASC Topic 606 that permits the entity to recognize revenue as invoiced. See Note 14 for the disaggregation of the Company's revenues
Rental Costs	Rental Costs Costs associated with rental activities are expensed as incurred and include advertising expenses, which were $20.2 million, $18.8 million, and $13.0 million for the years ended December 31, 2018, 2017, and 2016, respectively.
Real Estate Assets and Depreciation and Amortization	Real Estate Assets and Depreciation and Amortization Real estate assets are carried at depreciated cost and consist of land, buildings and improvements and other and development and capital improvements in progress (see "Development Costs" below). Repairs and maintenance costs are expensed as incurred, while significant improvements, renovations, and recurring capital replacements are capitalized and depreciated over their estimated useful lives. Recurring capital replacements typically include scheduled carpet replacement, new roofs, HVAC units, plumbing, concrete, masonry and other paving, pools and various exterior building improvements. In addition to these costs, the Company also capitalizes salary costs directly identifiable with renovation work. These expenditures extend the useful life of the property and increase the property’s fair market value. The cost of interior painting and blinds are typically expensed as incurred. Depreciation is computed on a straight-line basis over the estimated useful lives of the related assets, which range from five to 40 years. The Consolidated Balance Sheets line "Buildings and improvements and other" includes land improvements and buildings, which have a useful life ranging from eight to 40 years, as well as furniture, fixtures and equipment, which have a useful life of five years.
Development Costs	Development Costs Development projects and the related carrying costs, including interest, property taxes, insurance and allocated direct development salary cost during the construction period, are capitalized and reported in the accompanying Consolidated Balance Sheets as "Development and capital improvements in progress" during the construction period. Interest is capitalized in accordance with accounting standards governing the capitalization of interest. Upon completion and certification for occupancy of individual buildings or floors within a development, amounts representing the completed portion of total estimated development costs for the project are transferred to "Buildings and improvements and other" as real estate held for investment. Capitalization of interest, property taxes, insurance and allocated direct development salary costs cease upon the transfer. The assets are depreciated over their estimated useful lives. Total capitalized costs (including capitalized interest, salaries and real estate taxes) during the years ended December 31, 2018, 2017 and 2016 was $4.2 million, $11.0 million and $2.7 million, respectively. Certain costs associated with the lease-up of development projects, including cost of model units, furnishings and signs, are capitalized and amortized over their respective estimated useful lives. All other costs relating to renting development projects are expensed as incurred.
Acquisition of Real Estate Assets	Acquisition of Real Estate Assets In accordance with ASC Topic 805, Business Combinations, most acquisitions of operating properties qualify as an asset acquisition. Accordingly, the cost of the real estate acquired, including acquisition costs, is allocated to the acquired tangible assets, consisting of land, buildings and improvements and other, and identified intangible assets, consisting of the value of in-place leases and other contracts, on a relative fair value basis. Acquisition costs include appraisal fees, title fees, broker fees and other legal costs to acquire the property. The purchase price of an acquired property is allocated based on the relative fair value of the individual components as a proportion of the total assets acquired. The Company allocates the cost of the tangible assets of an acquired property by valuing the building as if it were vacant, based on management’s determination of the relative fair values of these assets. Management determines the as-if-vacant fair value of a building using methods similar to those used by independent appraisers. These methods include using stabilized net operating income, or NOI, and market specific capitalization and discount rates. In allocating the cost of identified intangible assets of an acquired property, the in-place leases are valued based on current rent rates and time and cost to lease a unit. Management concluded that the residential leases acquired in connection with each of its property acquisitions approximate at-market rates since the residential lease terms generally do not extend beyond one year. For residential leases, the fair value of the in-place leases and resident relationships is amortized over six months, which represents the estimated remaining term of the tenant leases. For commercial leases, the fair value of in-place leases and resident relationships is amortized over the remaining term of the commercial leases. The net amount of these lease intangibles included in "Other assets" totaled $3.9 million and $7.1 million as of December 31, 2018, and 2017, respectively. For the accounting policy on larger, portfolio style acquisitions which qualify as business combinations (rather than asset acquisitions), see Note 2.
Impairment of Long-lived Assets, including Goodwill	Impairment of Long-lived Assets The Company accounts for long-lived assets in accordance with the provisions of accounting standards for the impairment or disposal of long-lived assets. Management periodically evaluates long-lived assets, including investments in real estate, for indicators that would suggest that the carrying amount of the assets may not be recoverable. The judgments regarding the existence of such indicators are based on factors such as operating performance, market conditions and legal factors. Long-lived assets, such as real estate assets, equipment and purchased intangibles subject to amortization, are reviewed for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable. Recoverability of assets to be held and used is measured by a comparison of the carrying amount of an asset to estimated undiscounted future cash flows expected to be generated by the asset. If the carrying amount of an asset exceeds its estimated future cash flows, an impairment charge is recognized for the amount by which the carrying amount of the asset exceeds the fair value of the asset. Assets to be disposed of are separately presented in the Consolidated Balance Sheets and reported at the lower of the carrying amount or fair value less costs to sell, and are no longer depreciated. The assets and liabilities of a disposed group or a property classified as held for sale are presented separately in the appropriate asset and liability sections of the Consolidated Balance Sheets.
Undeveloped Land	Undeveloped Land Undeveloped land includes sites intended for future multifamily developments, sites for future commercial development and sites intended for residential use, which are carried at the lower of cost or fair value in accordance with GAAP and any costs incurred prior to commencement of pre-development activities are expensed as incurred.
Equity Method Investments	Investment 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 December 31, 2018 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 a 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 December 31, 2018, the Company's investment in the Apartment LLC totaled $44.2 million. In September 2017, a subsidiary of the Operating Partnership invested in a limited partnership, Real Estate Technology Ventures, L.P. As of December 31, 2018, Operating Partnership indirectly owned 20.7% of the limited partnership. The limited partnership was determined to be a VIE, but the Company is not designated as a 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 December 31, 2018, the Company's investment in the limited partnership totaled $3.8 million and is included in "Other assets" in the accompanying Consolidated Balance Sheet. As of December 31, 2018, the Company was committed to make additional capital contributions totaling $13.6 million if and when called by the general partner of the limited partnership and until September 2022.
Cash and Cash Equivalents	. Cash and Cash Equivalents Investments in money market accounts and certificates of deposit with original maturities of three months or less are considered to be cash equivalen
Restricted Cash	Restricted Cash Restricted cash consists of security deposits required to be held separately, escrow deposits held by lenders for property taxes, insurance, debt service and replacement reserves, and exchanges under Section 1031(b) of the Internal Revenue Code of 1986, as amended, or the Code. Section 1031(b) exchanges are presented within cash, cash equivalents and restricted cash reported in the Consolidated Statements of Cash Flows.
Other Assets	Other Assets Other assets consist primarily of receivables and deposits from residents, the value of derivative contracts, deferred rental concessions, deferred financing costs relating to lines of credit and other prepaid expenses. Also included in other assets are the fair market value of in-place leases and resident relationships, net of accumulated amortizat
Accrued Expenses and Other Liabilities	Accrued Expenses and Other Liabilities Accrued expenses consist of accrued dividends payable, accrued real estate taxes, accrued interest payable, accrued loss contingencies (see Note 12), accounts payable, fair market value of interest rate swaps (see Note 7), security deposits not related to restricted cash, other accrued expenses, and unearned income. Significant accruals include accrued dividends payable of $113.2 million and $108.7 million as of December 31, 2018 and 2017, respectively; accrued real estate taxes of $123.5 million and $99.6 million as of December 31, 2018 and 2017, respectively; unearned income of $41.1 million and $40.8 million as of December 31, 2018 and 2017, respectively; accrued loss contingencies of $8.7 million and $32.1 million as of December 31, 2018 and 2017, respectively; security deposits of $18.7 million and $19.1 million as of December 31, 2018 and 2017, respectively; and accrued interest payable of $15.1 million and $18.1 million as of December 31, 2018 and 2017, respective
Income Taxes	Income Taxes
Fair value of derivative financial instruments	Fair Value Measurements The Company applies the guidance in ASC Topic 820, Fair Value Measurements and Disclosures, to the valuation of real estate assets recorded at fair value, if any; to its impairment valuation analysis of real estate assets; to its disclosure of the fair value of financial instruments, principally indebtedness; and to its derivative financial instruments. Fair value disclosures required under ASC Topic 820 as well as the Company's derivative accounting policies are summarized in Note 7 utilizing the following hierarchy: 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 liabili
Recent Accounting Pronouncements	Impact of Recently Adopted Accounting Standards on Consolidated Statements of Cash Flows Effective January 1, 2018, the Company adopted ASU 2016-15, Classification of Certain Cash Receipts and Cash Payments, which clarifies how certain types of cash receipts and cash payments are to be presented and classified in the statement of cash flows. Management determined that three of the eight transactions in the ASU are relevant to the Company and its cash flows and include debt prepayment and extinguishment costs, proceeds from the settlement of insurance claims and distributions received from equity method investees. Upon adoption of ASU 2016-15, net cash provided by operating activities increased by $1.9 million and $0.6 million, respectively, net cash used in investing activities decreased by $0.2 million and $0.5 million, respectively, and net cash used in financing activities decreased by $1.7 million and $0.1 million, respectively, in the Consolidated Statements of Cash Flows for the years ended December 31, 2017 and December 31, 2016. The Company adopted ASU 2016-18, Statement of Cash Flows (Topic 230): Restricted Cash, effective January 1, 2018. The ASU required restricted cash to be presented within cash and cash equivalents when reconciling the beginning and ending amounts in the statement of cash flow with retrospective adjustments to all periods presented. The Company previously reported the change in restricted cash within the operating and investing activities in the consolidated statement of cash flows. Upon adoption, cash, cash equivalents and restricted cash reported in the Consolidated Statements of Cash Flows for the years ended December 31, 2017 and December 31, 2016 increased by $78.1 million and $88.3 million, respectively, to reflect the restricted cash balances. Additionally, net cash provided by operating activities increased by $0.4 million and $0.3 million, respectively, for the years ended December 31, 2017 and December 31, 2016. Net cash used in investing activities decreased by $10.6 million for the year ended December 31, 2017 and increased by $61.9 million for the year ended December 31, 2016. Recently Issued Accounting Pronouncements In 2016, the Financial Accounting Standards Board, or FASB, issued a new lease accounting standard, ASU 2016-02, Leases (Topic 842), which amends existing accounting standards and establishes new principles, presentation and disclosure requirements for lease accounting for both the lessee and lessor. Under the new standard, lessors will use an approach that is substantially equivalent to existing guidance but aligned with the recently adopted revenue recognition standard, while lessees will be required to record most leases on the balance sheet and recognize lease expense in the income statement in a manner similar to current practice. The new standard requires a lessee to recognize a lease liability for the obligation to make lease payments and a right-of-use asset for the right to use the underlying asset for all leases with terms of more than twelve months. Expenses related to leases determined to be operating leases will be recognized on a straight-line basis, while those determined to be financing leases will be recognized following a front-loaded expense profile in which interest and amortization are presented separately in the income statement. The Company has completed its analysis of lease revenues and the impact this standard will have on the Company. Management elected to apply the modified retrospective transition approach upon adoption of ASU 2016-02 on January 1, 2019. The adoption of the new lease standard has not resulted in significant changes in the accounting for the Company's lease revenues as the Company’s residential and retail/commercial leases, where it is the lessor, will continue to be accounted for as operating leases. Management has elected available practical expedients that provide lessors an option to not separate lease and non-lease components when certain criteria are met, and instead, allows for those components to be accounted for as a single lease component. The Company is the lessee under certain ground, office, equipment and other operating leases and is required to recognize a right-of-use asset and a corresponding lease obligation on its Consolidated Balance Sheets for those leases effective January 1, 2019. Based on its election of available practical expedients, the Company is not required to reassess the classification of existing leases; therefore, these leases will continue to be accounted for as operating leases. Upon adoption of the standard on January 1, 2019, the Company expects to recognize total right-of-use assets of approximately $43 million and related lease obligations of approximately $33 million. The guidance does require additional disclosures regarding the nature and timing of the Company's lease transactions upon adoption, which will be included in the Company's first quarter Quarterly Report on Form 10-Q filing in 2019.