AvalonBay Communities (AVB) 10-Q 2 May 17 2017 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2017	Apr. 28, 2017
Document and Entity Information
Entity Registrant Name	AVALONBAY COMMUNITIES INC
Entity Central Index Key	915,912
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Document Type	10-Q
Document Period End Date	Mar. 31, 2017
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	Q1
Amendment Flag	false
Entity Common Stock, Shares Outstanding		137,786,073

CONDENSED CONSOLIDATED BALANCE

CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Real estate:
Land and improvements	$ 3,981,847	$ 3,941,250
Buildings and improvements	14,496,026	14,314,981
Furniture, fixtures and equipment	546,523	532,994
Gross operating real estate	19,024,396	18,789,225
Less accumulated depreciation	(3,852,593)	(3,743,632)
Net operating real estate	15,171,803	15,045,593
Construction in progress, including land	1,791,134	1,882,262
Land held for development	103,954	84,293
Real estate assets held for sale, net	0	20,846
Total real estate, net	17,066,891	17,032,994
Cash and cash equivalents	121,705	214,994
Cash in escrow	247,015	114,983
Resident security deposits	32,167	32,071
Investments in unconsolidated real estate entities	183,403	175,116
Deferred development costs	40,110	40,179
Prepaid expenses and other assets	287,130	256,934
Total assets	17,978,421	17,867,271
LIABILITIES AND EQUITY
Unsecured notes, net	4,464,546	4,463,302
Variable rate unsecured credit facility	0	0
Mortgage notes payable, net	2,541,183	2,567,578
Dividends payable	195,657	185,397
Payables for construction	96,672	100,998
Accrued expenses and other liabilities	293,637	274,676
Accrued interest payable	54,143	38,307
Resident security deposits	57,183	57,023
Liabilities related to real estate assets held for sale	0	808
Total liabilities	7,703,021	7,688,089
Commitments and contingencies
Redeemable noncontrolling interests	8,778	7,766
Equity:
Preferred stock, $0.01 par value; $25 liquidation preference; 50,000,000 shares authorized at March 31, 2017 and December 31, 2016; zero shares issued and outstanding at March 31, 2017 and December 31, 2016	0	0
Common stock, $0.01 par value; 280,000,000 shares authorized at March 31, 2017 and December 31, 2016; 137,786,600 and 137,330,904 shares issued and outstanding at March 31, 2017 and December 31, 2016, respectively	1,378	1,373
Additional paid-in capital	10,160,183	10,105,654
Accumulated earnings less dividends	133,674	94,899
Accumulated other comprehensive loss	(28,613)	(30,510)
Total equity	10,266,622	10,171,416
Total liabilities and equity	$ 17,978,421	$ 17,867,271

CONDENSED CONSOLIDATED BALANCE3

CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Mar. 31, 2017	Dec. 31, 2016
Statement of Financial Position [Abstract]
Preferred stock, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred stock, liquidation preference (in dollars per share)	$ 25	$ 25
Preferred stock, shares authorized (in shares)	50,000,000	50,000,000
Preferred stock, shares issued (in shares)	0	0
Preferred stock, shares outstanding (in shares)	0	0
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	280,000,000	280,000,000
Common stock, shares issued (in shares)	137,786,600	137,330,904
Common stock, shares outstanding (in shares)	137,786,600	137,330,904

CONDENSED CONSOLIDATED STATEMEN

CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Revenue:
Rental and other income	$ 521,126	$ 506,974
Management, development and other fees	1,200	1,524
Total revenue	522,326	508,498
Expenses:
Operating expenses, excluding property taxes	123,044	116,626
Property taxes	52,930	50,067
Interest expense, net	49,295	43,410
Depreciation expense	140,621	127,216
General and administrative expense	13,206	11,404
Expensed acquisition, development and other pursuit costs, net of recoveries	728	3,462
Casualty and impairment loss (gain), net	(11,688)	2,202
Total expenses	391,512	349,983
Income before equity in income of unconsolidated real estate entities, gain on sale of communities and other real estate, and income taxes	130,814	158,515
Equity in income of unconsolidated real estate entities	16,672	27,969
Gain on sale of communities	87,949	51,430
Gain on sale of other real estate	366	0
Income before income taxes	235,801	237,914
Income tax expense	20	37
Net income	235,781	237,877
Net loss attributable to noncontrolling interests	94	54
Net income attributable to common stockholders	235,875	237,931
Other comprehensive income (loss):
(Loss) income on cash flow hedges	145	(47,757)
Cash flow hedge losses reclassified to earnings	1,752	1,374
Comprehensive income	$ 237,772	$ 191,548
Earnings per common share - basic:
Net income attributable to common stockholders (in dollars per share)	$ 1.72	$ 1.73
Earnings per common share - diluted:
Net income attributable to common stockholders (in dollars per share)	1.72	1.73
Dividends per common share (in dollars per share)	$ 1.42	$ 1.35

CONDENSED CONSOLIDATED STATEME5

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Cash flows from operating activities:
Net income	$ 235,781	$ 237,877
Adjustments to reconcile net income to cash provided by operating activities:
Depreciation expense	140,621	127,216
Amortization of deferred financing costs	1,826	1,936
Amortization of debt premium	(4,621)	(4,779)
Amortization of stock-based compensation	4,319	3,835
Equity in (income) loss of, and return on, unconsolidated real estate entities and noncontrolling interests, net of eliminations	(5,768)	6,438
Casualty and impairment loss (gain), net	11,688	(2,202)
Abandonment of development pursuits	265	0
Cash flow hedge losses reclassified to earnings	1,752	1,374
Gain on sale of real estate assets	(97,012)	(81,055)
(Increase) decrease in cash in operating escrows	(6,433)	3,009
Increase in resident security deposits, prepaid expenses and other assets	(10,630)	(8,559)
Increase (decrease) in accrued expenses, other liabilities and accrued interest payable	21,674	(7,308)
Net cash provided by operating activities	293,462	277,782
Cash flows from investing activities:
Development/redevelopment of real estate assets including land acquisitions and deferred development costs	(259,573)	(266,588)
Acquisition of real estate assets, including partnership interest	0	(170,022)
Capital expenditures - existing real estate assets	(8,015)	(11,618)
Capital expenditures - non-real estate assets	(2,429)	(3,264)
Proceeds from sale of real estate, net of selling costs	159,985	68,709
Increase in cash in deposit escrows	(126,467)	(69,227)
Insurance proceeds for property damage claims	4,095	8,702
Mortgage note receivable lending	(4,795)	0
(Decrease) increase in payables for construction	(4,326)	842
Distributions from unconsolidated real estate entities	11,952	58,652
Investments in unconsolidated real estate entities	(5,774)	(913)
Net cash used in investing activities	(235,347)	(384,727)
Cash flows from financing activities:
Issuance of common stock, net	56,817	1,102
Dividends paid	(185,192)	(171,151)
Repayments of mortgage notes payable, including prepayment penalties	(21,037)	(19,682)
Payment of deferred financing costs	(2,315)	(6,176)
Distributions to DownREIT partnership unitholders	(11)	(10)
Contributions from joint venture and profit-sharing partners	1,038	0
Distributions to joint venture and profit-sharing partners	(104)	(104)
Preferred interest obligation redemption and dividends	(600)	0
Net cash used in financing activities	(151,404)	(196,021)
Net decrease in cash and cash equivalents	(93,289)	(302,966)
Cash and cash equivalents, beginning of period	214,994	400,507
Cash and cash equivalents, end of period	121,705	97,541
Cash paid during the period for interest, net of amount capitalized	$ 34,503	$ 46,011

CONDENSED CONSOLIDATED STATEME6

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Parenthetical) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Supplemental disclosures of non-cash investing and financing activities
Common stock issued through the dividend reinvestment plan (in shares)	1,165	576
Common stock issued through the dividend reinvestment plan	$ 205	$ 101
Number of shares withheld to satisfy employees' tax withholding and other liabilities (in shares)	57,172	48,189
Shares withheld to satisfy employees' tax withholding and other liabilities, value	$ 10,149	$ 8,164
Stock Issued During Period, Shares, Share-based Compensation, Forfeited (in shares)	236
Stock Issued During Period, Value, Share-based Compensation, Forfeited	$ 41	76
Dividends declared but not paid	195,657	185,173
Change in redemption value of redeemable noncontrolling interest	(183)
Increase (Decrease) in Prepaid Expense and Other Assets	(180)	5,422
(Loss) income on cash flow hedges	145	(47,757)
Increase in accrued expenses, other liabilities and accrued interest payable	102	42,335
Cash flow hedge losses reclassified to earnings	1,752	1,374
Net operating real estate	15,171,803
Prepaid expenses and other assets	287,130
Avalon Maplewood [Member]
Supplemental disclosures of non-cash investing and financing activities
Net operating real estate	16,361
Prepaid expenses and other assets	$ 12,598
Mortgage notes payable | Notes Payable Maturities 2020 [Member] | Avalon Hoboken [Member]
Supplemental disclosures of non-cash investing and financing activities
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Long-term Debt		$ 67,904
Restricted Stock and Restricted Stock Converted From Performance Shares [Member]
Supplemental disclosures of non-cash investing and financing activities
Restricted stock granted (in shares)	198,502	193,171
Restricted Stock Converted From Performance Shares [Member]
Supplemental disclosures of non-cash investing and financing activities
Restricted stock granted (in shares)	128,482	115,618
Restricted stock
Supplemental disclosures of non-cash investing and financing activities
Restricted stock granted (in shares)	70,020	77,553
Fair value of shares issued	$ 12,538	$ 12,529
Stock Issued During Period, Shares, Share-based Compensation, Forfeited (in shares)	236	499
Retained Earnings [Member]
Supplemental disclosures of non-cash investing and financing activities
Change in redemption value of redeemable noncontrolling interest	$ (183)	$ 299

Organization, Basis of Presenta

Organization, Basis of Presentation and Significant Accounting Policies	3 Months Ended
	Mar. 31, 2017
Accounting Policies [Abstract]
Organization, Basis of Presentation and Significant Accounting Policies	Organization, Basis of Presentation and Significant Accounting Policies Organization and Basis of Presentation AvalonBay Communities, Inc. (the "Company," which term, unless the context otherwise requires, refers to AvalonBay Communities, Inc. together with its subsidiaries), is a Maryland corporation that has elected to be treated as a real estate investment trust ("REIT") for federal income tax purposes under the Internal Revenue Code of 1986 (the "Code"). The Company focuses on the development, redevelopment, acquisition, ownership and operation of multifamily communities primarily in New England, the New York/New Jersey metro area, the Mid-Atlantic, the Pacific Northwest, and Northern and Southern California. At March 31, 2017 , the Company owned or held a direct or indirect ownership interest in 260 operating apartment communities containing 74,952 apartment homes in 10 states and the District of Columbia, of which nine communities containing 4,075 apartment homes were under redevelopment. In addition, the Company owned or held a direct or indirect ownership interest in 24 communities under development that are expected to contain an aggregate of 7,581 apartment homes when completed. The Company also owned or held a direct or indirect ownership interest in land or rights to land on which the Company expects to develop an additional 28 communities that, if developed as expected, will contain an estimated 9,304 apartment homes. The interim unaudited financial statements have been prepared in accordance with U.S. generally accepted accounting principles ("GAAP") for interim financial information and in conjunction with the rules and regulations of the Securities and Exchange Commission ("SEC"). Certain information and footnote disclosures normally included in financial statements required by GAAP have been condensed or omitted pursuant to such rules and regulations. These unaudited financial statements should be read in conjunction with the financial statements and notes included in the Company's 2016 Annual Report on Form 10-K. The results of operations for the three months ended March 31, 2017 are not necessarily indicative of the operating results for the full year. Management believes the disclosures are adequate to ensure the information presented is not misleading. In the opinion of management, all adjustments and eliminations, consisting only of normal, recurring adjustments necessary for a fair presentation of the financial statements for the interim periods, have been included. Capitalized terms used without definition have meanings provided elsewhere in this Form 10-Q. Earnings per Common Share Basic earnings per share is computed by dividing net income attributable to common stockholders by the weighted average number of shares outstanding during the period. All outstanding unvested restricted share awards contain rights to non-forfeitable dividends and participate in undistributed earnings with common shareholders and, accordingly, are considered participating securities that are included in the two-class method of computing basic earnings per share ("EPS"). Both the unvested restricted shares and other potentially dilutive common shares, and the related impact to earnings, are considered when calculating earnings per share on a diluted basis. The Company's earnings per common share are determined as follows (dollars in thousands, except per share data): For the three months ended 3/31/2017 3/31/2016 Basic and diluted shares outstanding Weighted average common shares - basic 137,068,874 136,785,880 Weighted average DownREIT units outstanding 7,500 7,500 Effect of dilutive securities 454,868 589,664 Weighted average common shares - diluted 137,531,242 137,383,044 Calculation of Earnings per Share - basic Net income attributable to common stockholders $ 235,875 $ 237,931 Net income allocated to unvested restricted shares (652 ) (632 ) Net income attributable to common stockholders, adjusted $ 235,223 $ 237,299 Weighted average common shares - basic 137,068,874 136,785,880 Earnings per common share - basic $ 1.72 $ 1.73 Calculation of Earnings per Share - diluted Net income attributable to common stockholders $ 235,875 $ 237,931 Add: noncontrolling interests of DownREIT unitholders in consolidated partnerships 11 10 Adjusted net income attributable to common stockholders $ 235,886 $ 237,941 Weighted average common shares - diluted 137,531,242 137,383,044 Earnings per common share - diluted $ 1.72 $ 1.73 All options to purchase shares of common stock outstanding as of March 31, 2017 and 2016 are included in the computation of diluted earnings per share. As discussed under "Recently Issued and Adopted Accounting Standards," as of January 1, 2017, the Company adopted the provision of ASU 2016-09 using the modified retrospective approach to recognize forfeitures as they occur. Prior to the adoption of this standard, the Company was required to estimate the forfeiture of stock options and recognized compensation cost net of the estimated forfeitures. The estimated forfeitures included in compensation cost were adjusted to reflect actual forfeitures at the end of the vesting period. The change in accounting principle had an immaterial effect on the Company's financial position and no adjustment to retained earnings or the Company's diluted shares outstanding, as prescribed under the modified retrospective approach, was required in the prior year period. Derivative Instruments and Hedging Activities The Company enters into interest rate swap and interest rate cap agreements (collectively, "Hedging Derivatives") for interest rate risk management purposes and in conjunction with certain variable rate secured debt to satisfy lender requirements. The Company does not enter into Hedging Derivative transactions for trading or other speculative purposes. The Company assesses the effectiveness of qualifying cash flow and fair value hedges, both at inception and on an on-going basis. Hedge ineffectiveness is reported as a component of general and administrative expenses. The fair values of Hedging Derivatives that are in an asset position are recorded in prepaid expenses and other assets. The fair value of Hedging Derivatives that are in a liability position are included in accrued expenses and other liabilities. The Company does not present or disclose the fair value of Hedging Derivatives on a net basis. Fair value changes for derivatives that are not in qualifying hedge relationships are reported as a component of interest expense, net. For the Hedging Derivative positions that the Company has determined qualify as effective cash flow hedges, the Company has recorded the effective portion of cumulative changes in the fair value of Hedging Derivatives in other comprehensive income (loss). Amounts recorded in other comprehensive income (loss) will be reclassified into earnings in the periods in which earnings are affected by the hedged cash flow. The effective portion of the change in fair value of the Hedging Derivatives that the Company has determined qualified as effective fair value hedges is reported as an adjustment to the carrying amount of the corresponding debt being hedged. See Note 10, "Fair Value," for further discussion of derivative financial instruments. Legal and Other Contingencies Maplewood Casualty Loss In February 2017, a fire occurred at the Company's Avalon Maplewood Development Community, located in Maplewood, NJ, which was under construction and not yet occupied. The Company believes that liabilities to third parties resulting from the fire will not be material and will, in any event, be substantially covered by insurance subject to a deductible. The Company has commenced reconstruction of the damaged and destroyed portions of the community. See Note 5, "Investments in Real Estate Entities," for further discussion of the casualty gains and losses associated with the Maplewood casualty loss. Edgewater Casualty Loss In January 2015, a fire occurred at the Company's Avalon at Edgewater apartment community located in Edgewater, New Jersey ("Edgewater"). Edgewater consisted of two residential buildings. One building, containing 240 apartment homes, was destroyed. The second building, containing 168 apartment homes, suffered minimal damage and has been repaired. The Company has established protocols for processing claims from third parties who suffered losses as a result of the fire, and many third parties have contacted the Company's insurance carrier and settled their claims. See Part II, Item 1, "Legal Proceedings," for further discussion of the lawsuits associated with the Edgewater casualty loss. Three class action lawsuits have been filed against the Company on behalf of occupants of the destroyed building and consolidated in the United States District Court for the District of New Jersey. The Company has agreed with class counsel to the terms of a proposed settlement which would provide a claims process (with agreed upon protocols for instructing the adjuster as to how to evaluate claims) and, if needed, an arbitration process to determine damage amounts to be paid to individual claimants covered by the class settlement. In March 2017 the District Court granted preliminary approval of the class action settlement and in July 2017 a fairness hearing will be held to determine whether the settlement will receive final approval. A fourth class action, being heard in the same federal court, was filed against the Company on behalf of residents of the second Edgewater building that suffered minimal damage. Recently, a fifth class action lawsuit was filed against the Company seeking to certify a class on behalf of both buildings and other third parties. That action is currently stayed pending the decision by those plaintiffs either to be included in the class settlement or to formally opt-out. In addition to the class action lawsuits described above, 19 lawsuits representing approximately 146 individual plaintiffs have been filed and are currently pending in the Superior Court of New Jersey Bergen County - Law Division. All of these state court cases have been consolidated by the court. These plaintiffs, if eligible to be class members under the class settlement that has been preliminarily approved as described above, must formally opt-out of that class action settlement by May 17, 2017 if they want to continue their individual actions. The Company believes that it has meritorious defenses to the extent of damages claimed in all of the suits. There are also five subrogation lawsuits that have been filed against the Company by insurers of Edgewater residents who obtained renters insurance; it is the Company's position that in the majority of the applicable leases the residents waived subrogation rights. One of these lawsuits has been dismissed on that basis and the other four are currently pending in the United States District Court for the District of New Jersey. The District Court recently denied the Company's motions seeking dismissal on this basis. The Company will reassess the viability of this defense after conducting additional discovery. Having settled many third party claims through the insurance claims process, the Company currently believes that any potential remaining liability to third parties (including any potential liability to third parties determined in accordance with the class settlement described above, if approved) will not be material to the Company and will in any event be substantially covered by the Company's insurance policies. However, the Company can give no assurances in this regard and continues to evaluate this matter. See Note 5, "Investments in Real Estate Entities," and Part II, Item 1, "Legal Proceedings," for further discussion of the casualty gains and losses and lawsuits associated with the Edgewater casualty loss. Other Matters The Company is involved in various other claims and/or administrative proceedings unrelated to the Edgewater casualty loss that arise in the ordinary course of its business. While no assurances can be given, the Company does not currently believe that any of these other outstanding litigation matters, individually or in the aggregate, will have a material adverse effect on its financial condition or results of operations. Acquisitions of Investments in Real Estate The Company accounts for acquisitions of investments in real estate in accordance with the authoritative guidance for the initial measurement, which requires the identifiable assets acquired, the liabilities assumed and any noncontrolling interest in the acquiree to be recognized at fair value. Typical assets and liabilities acquired include land, building, furniture, fixtures and equipment, debt and identified intangible assets and liabilities, consisting of the value of above or below market leases and in-place leases. In making estimates of fair values for purposes of allocating purchase price, the Company utilizes various sources, including its own analysis of recently acquired and existing comparable properties in its portfolio and other market data. Consideration for acquisitions is typically in the form of cash unless otherwise disclosed. For an acquisition of a business, the allocation of the purchase price is based on the fair value of the net assets, and for an asset acquisition, the allocation of the purchase price is based on the relative fair value of the net assets. Subsequent to the adoption of ASU 2017-01 on October 1, 2016, the Company expects that acquisitions of individual operating communities will generally be viewed as asset acquisitions. Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make certain estimates and assumptions. These estimates and assumptions affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the dates of the financial statements and the reported amounts of revenue and expenses during the reporting periods. Actual results could differ from those estimates. Reclassifications Certain reclassifications have been made to amounts in prior years' notes to financial statements to conform to current year presentations as a result of changes in held for sale classification and disposition activity. Recently Issued Accounting Standards In February 2017, the Financial Accounting Standards Board ("FASB") issued Accounting Standards Update ("ASU") 2017-05, Other Income-Gains and Losses from the Derecognition of Nonfinancial Assets (Subtopic 610-20): Clarifying the Scope of Asset Derecognition Guidance and Accounting for Partial Sales of Nonfinancial Assets. This ASU clarifies the scope of the nonfinancial asset guidance and the derecognition of all businesses and nonprofit activities (except those related to conveyances of oil and gas mineral rights or contracts with customers). In addition, the amendments eliminate the exception in the financial asset guidance for transfers of investments (including equity method investments) in real estate entities and supersede the guidance in the Exchanges of a Nonfinancial Asset for a Noncontrolling Ownership Interest. The amendments also provide guidance on the accounting of partial sales of nonfinancial assets and contributions of nonfinancial assets to a joint venture or other noncontrolled investee. The new standard allows for either a retrospective or modified retrospective approach. The guidance will be effective in the first quarter of 2018 and allows for early adoption. The Company is assessing whether the new standard will have a material effect on its financial position or results of operations. In August 2016, the FASB issued ASU 2016-15, Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments. This ASU addresses eight specific cash flow issues including debt prepayment or debt extinguishment costs, proceeds from the settlement of insurance claims, distributions received from equity method investees and separately identifiable cash flows and application of the predominance principle. The new standard requires a retrospective approach. The guidance will be effective in the first quarter of 2018 and allows for early adoption. The Company adopted this guidance as of January 1, 2017. The new standard did not have a material effect on the Company's Condensed Consolidated Statements of Cash Flows. In March 2016, the FASB issued ASU 2016-09, Compensation-Stock Compensation: Improvements to Employee Share-Based Payment Accounting, which simplifies several aspects of share-based payment transactions, including income tax consequences, classification of awards as equity or liability, statement of cash flows classification and policy election options for forfeitures. Upon adoption of the standard, the Company elected to account for forfeitures when they occur instead of estimating the forfeitures. The Company adopted this guidance as of January 1, 2017, using the modified retrospective approach. The new standard did not have a material effect on the Company's financial position, results of operations or earnings per share as discussed in "Earnings per Common Share." In February 2016, the FASB issued ASU 2016-02, Leases, amending the existing accounting standards for lease accounting, including requiring lessees to recognize most leases on their balance sheets and making targeted changes to lessor accounting. The guidance will be effective in the first quarter of 2019 and allows for early adoption. The new standard requires a modified retrospective transition approach for all leases existing at, or entered into after, the date of initial application, with an option to use certain transition relief. ASU 2016-02 provides for transition relief, which includes not electing to (i) reassess whether any expired or existing contract is a lease or contains a lease, (ii) reassess the lease classification of any expired or existing leases and (iii) expense any capitalized initial direct costs for any existing leases. The Company anticipates adoption of the standard to have a material impact on its financial position and results of operations resulting from the recognition of the right to use asset and corresponding lease obligation for its long-term ground leases, currently accounted for as operating leases. The Company will continue to assess the impact of the new standard. In May 2014, the FASB issued ASU 2014-09, Revenue from Contracts with Customers and in August 2015, the FASB issued ASU 2015-14, Revenue from Contracts with Customers-Deferral of the Effective Date, which defers the effective date of the new revenue recognition standard until the first quarter of 2018. Subsequently, the FASB has issued multiple ASUs clarifying ASU 2014-09 and ASU 2015-14. Under the new standard, revenue is recognized when persuasive evidence of an arrangement exists, delivery has occurred, the fee is fixed or determinable, and collectability is probable. Revenue is generally recognized net of allowances and any taxes collected from customers and subsequently remitted to governmental authorities. The majority of the Company's revenue is derived from rental income, which is scoped out from this standard and will be accounted for under ASU 2016-02, Leases, discussed above. The Company's other revenue streams, which are being evaluated under this ASU, include but are not limited to management fees, other income from residents determined not to be within the scope of ASU 2016-02 and gains and losses from real estate dispositions. The Company will continue to assess the impact of the new standard and anticipates adoption as of January 1, 2018 using the modified retrospective approach.

Interest Capitalized

Interest Capitalized	3 Months Ended
	Mar. 31, 2017
Interest Capitalized
Interest Capitalized	Interest Capitalized The Company capitalizes interest during the development and redevelopment of real estate assets. Capitalized interest associated with the Company's development or redevelopment activities totaled $17,821,000 and $20,609,000 for the three months ended March 31, 2017 and 2016 , respectively.

Mortgage Notes Payable, Unsecur

Mortgage Notes Payable, Unsecured Notes and Credit Facility	3 Months Ended
	Mar. 31, 2017
Debt Disclosure [Abstract]
Notes Payable, Unsecured Notes and Credit Facility	Mortgage Notes Payable, Unsecured Notes and Credit Facility The Company's mortgage notes payable, unsecured notes, variable rate unsecured term loans ("Term Loans") and Credit Facility, as defined below, as of March 31, 2017 and December 31, 2016 are summarized below. The following amounts and discussion do not include the mortgage notes related to the communities classified as held for sale, if any, as of March 31, 2017 and December 31, 2016 , as shown in the accompanying Condensed Consolidated Balance Sheets (dollars in thousands) (see Note 6, "Real Estate Disposition Activities"). 3/31/2017 12/31/2016 Fixed rate unsecured notes (1) $ 4,200,000 $ 4,200,000 Term Loans (1) 300,000 300,000 Fixed rate mortgage notes payable - conventional and tax-exempt (2) 1,664,650 1,668,496 Variable rate mortgage notes payable - conventional and tax-exempt (2) 890,202 908,262 Total mortgage notes payable and unsecured notes 7,054,852 7,076,758 Credit Facility — — Total mortgage notes payable, unsecured notes and Credit Facility $ 7,054,852 $ 7,076,758 _____________________________________ (1) Balances at March 31, 2017 and December 31, 2016 exclude $8,640 and $8,930 , respectively, of debt discount, and $26,814 and $27,768 , respectively, of deferred financing costs, as reflected in unsecured notes, net on the accompanying Condensed Consolidated Balance Sheets. (2) Balances at March 31, 2017 and December 31, 2016 exclude $3,044 of debt discount and $1,866 of debt premium, respectively, and $10,625 and $11,046 , respectively, of deferred financing costs, as reflected in mortgage notes payable on the accompanying Condensed Consolidated Balance Sheets. The following debt activity occurred during the three months ended March 31, 2017 : • In February 2017, the Company repaid $17,300,000 of variable rate debt secured by Avalon Mountain View at par at its scheduled maturity date. • In February 2017, the Company entered into a $250,000,000 variable rate unsecured term loan (the " $250 million Term Loan"), of which $100,000,000 matures in February 2022 with stated pricing of LIBOR plus 0.90% , and $150,000,000 matures in February 2024 with stated pricing of LIBOR plus 1.50% . As of March 31, 2017 , the Company had not drawn any of the available $250,000,000 under the variable rate unsecured term loan. See Note 11, "Subsequent Events," for further discussion. At March 31, 2017 , the Company has a $1,500,000,000 revolving variable rate unsecured credit facility with a syndicate of banks (the "Credit Facility") which matures in April 2020. The Company may extend the maturity for up to nine months , provided the Company is not in default and upon payment of a $1,500,000 extension fee. The Credit Facility bears interest at varying levels based on the London Interbank Offered Rate ("LIBOR"), rating levels achieved on the Company's unsecured notes and on a maturity schedule selected by the Company. The current stated pricing is LIBOR plus 0.825% per annum ( 1.81% at March 31, 2017 ), assuming a one month borrowing rate. The annual facility fee is 0.125% (or approximately $1,875,000 annually based on the $1,500,000,000 facility size and based on the Company's current credit rating). The Company had no borrowings outstanding under the Credit Facility and had $45,084,000 and $46,711,000 outstanding in letters of credit that reduced the borrowing capacity as of March 31, 2017 and December 31, 2016 , respectively. In the aggregate, secured notes payable mature at various dates from November 2017 through July 2066, and are secured by certain apartment communities (with a net carrying value of $3,405,173,000 , excluding communities classified as held for sale, as of March 31, 2017 ). As of March 31, 2017 , the Company has guaranteed a $100,000,000 mortgage note payable held by a wholly-owned subsidiary; such mortgage note payable is consolidated for financial reporting purposes. The weighted average interest rate of the Company's fixed rate mortgage notes payable (conventional and tax-exempt) was 4.4% at both March 31, 2017 and December 31, 2016 . The weighted average interest rate of the Company's variable rate mortgage notes payable (conventional and tax-exempt), the Term Loan and its Credit Facility, including the effect of certain financing related fees, was 2.5% and 2.3% at March 31, 2017 and December 31, 2016 , respectively. Scheduled payments and maturities of mortgage notes payable and unsecured notes outstanding at March 31, 2017 are as follows (dollars in thousands): Year Secured notes payments Secured notes maturities Unsecured notes maturities Stated interest rate of unsecured notes 2017 13,954 692,191 — N/A 2018 17,789 76,667 — N/A 2019 4,696 655,514 — N/A 2020 3,624 118,729 250,000 6.100 % 400,000 3.625 % 2021 3,551 27,844 250,000 3.950 % 300,000 LIBOR + 1.450% 2022 3,795 — 450,000 2.950 % 2023 4,040 — 350,000 4.200 % 250,000 2.850 % 2024 4,310 — 300,000 3.500 % 2025 4,585 84,835 525,000 3.450 % 300,000 3.500 % 2026 4,894 — 475,000 2.950 % 300,000 2.900 % Thereafter 213,754 620,080 350,000 3.900 % $ 278,992 $ 2,275,860 $ 4,500,000 The Company was in compliance at March 31, 2017 with customary financial and other covenants under the Credit Facility, the Term Loans and the Company's fixed rate unsecured notes.

Equity

Equity	3 Months Ended
	Mar. 31, 2017
Stockholders' Equity Note [Abstract]
Equity	Equity The following summarizes the changes in equity for the three months ended March 31, 2017 (dollars in thousands): Common stock Additional paid-in capital Accumulated earnings less dividends Accumulated other comprehensive loss Total equity Balance at December 31, 2016 $ 1,373 $ 10,105,654 $ 94,899 $ (30,510 ) $ 10,171,416 Net income attributable to common stockholders — — 235,875 — 235,875 Gain on cash flow hedges, net — — — 145 145 Cash flow hedge loss reclassified to earnings — — — 1,752 1,752 Change in redemption value of redeemable noncontrolling interest — — (183 ) — (183 ) Dividends declared to common stockholders — — (195,657 ) — (195,657 ) Issuance of common stock, net of withholdings 5 47,962 (1,260 ) — 46,707 Amortization of deferred compensation — 6,567 — — 6,567 Balance at March 31, 2017 $ 1,378 $ 10,160,183 $ 133,674 $ (28,613 ) $ 10,266,622 As of March 31, 2017 and December 31, 2016 , the Company's charter authorized a total of 280,000,000 shares of common stock and 50,000,000 shares of preferred stock for issuance. During the three months ended March 31, 2017 , the Company: i. issued 7,266 shares of common stock in connection with stock options exercised; ii. issued 1,165 common shares through the Company's dividend reinvestment plan; iii. issued 198,502 common shares in connection with restricted stock grants and the conversion of performance awards to restricted shares; iv. issued 306,177 shares under CEP IV as discussed below; v. withheld 57,172 common shares to satisfy employees' tax withholding and other liabilities; and vi. canceled 236 common shares of restricted stock upon forfeiture. Any deferred compensation related to the Company's stock option, restricted stock and performance award grants during the three months ended March 31, 2017 is not reflected on the accompanying Condensed Consolidated Balance Sheet as of March 31, 2017 , and will not be reflected until recognized as compensation cost. In December 2015, the Company commenced a fourth continuous equity program ("CEP IV") under which the Company may sell up to $1,000,000,000 of its common stock from time to time. Actual sales will depend on a variety of factors to be determined by the Company, including market conditions, the trading price of the Company's common stock and determinations by the Company of the appropriate sources of funding for the Company. In conjunction with CEP IV, the Company engaged sales agents who will receive compensation of up to 2.0% of the gross sales price for shares sold. CEP IV also allows the Company to enter into forward sale agreements up to $1,000,000,000 in aggregate sales price of its common stock. The Company expects that it will physically settle each forward sale agreement on one or more dates specified by the Company on or prior to the maturity date of that particular forward sale agreement, in which case the Company will expect to receive aggregate net cash proceeds at settlement equal to the number of shares underlying the particular forward agreement multiplied by the relevant forward sale price. However, the Company may also elect to cash settle or net share settle a forward sale agreement. In connection with each forward sale agreement, the Company will pay the relevant forward seller, in the form of a reduced initial forward sale price, a commission of up to 2.0% of the sales prices of all borrowed shares of common stock sold. During the three months ended March 31, 2017 , the Company sold 306,177 shares at an average sales price of $186.44 per share, for net proceeds of $56,228,000 . As of March 31, 2017 , the Company had $942,915,000 of shares remaining authorized for issuance under this program.

Investments in Real Estate Enti

Investments in Real Estate Entities	3 Months Ended
	Mar. 31, 2017
Equity Method Investments and Joint Ventures [Abstract]
Investments in Real Estate Entities	Investments in Real Estate Entities Investment in Unconsolidated Real Estate Entities As of March 31, 2017 , the Company had investments in five unconsolidated real estate entities with ownership interest percentages ranging from 20.0% to 31.3% , excluding development joint ventures and joint ventures formed with Equity Residential as part of the Archstone acquisition. The Company accounts for its investments in unconsolidated real estate entities under the equity method of accounting. The significant accounting policies of the Company's unconsolidated real estate entities are consistent with those of the Company in all material respects. During the three months ended March 31, 2017 , AvalonBay Value Added Fund II, L.P. ("Fund II") sold Eaves Gaithersburg, located in Gaithersburg, MD, containing 684 apartment homes, for $117,000,000 . The Company's share of the gain in accordance with GAAP for the disposition was $8,697,000 , which is reported as a component of equity in income of unconsolidated real estate entities on the accompanying Condensed Consolidated Statements of Comprehensive Income. In conjunction with the disposition of this community during the three months ended March 31, 2017 , Fund II repaid $63,200,000 of secured indebtedness at par in advance of its scheduled maturity date. The Company has an equity interest of 31.3% in Fund II, and upon achievement of a threshold return, the Company has a right to incentive distributions for its promoted interest based on the current returns earned by Fund II, which represents 20.0% of further Fund II distributions, which is in addition to its proportionate share of the remaining 80.0% of distributions. During the three months ended March 31, 2017 , the Company recognized income of $6,765,000 for its promoted interest, which is reported as a component of equity in income of unconsolidated real estate entities on the accompanying Condensed Consolidated Statements of Comprehensive Income. The following is a combined summary of the financial position of the entities accounted for using the equity method discussed above as of the dates presented (dollars in thousands): 3/31/2017 12/31/2016 (unaudited) (unaudited) Assets: Real estate, net $ 862,612 $ 954,493 Other assets 76,208 49,519 Total assets $ 938,820 $ 1,004,012 Liabilities and partners' capital: Mortgage notes payable, net and credit facility $ 625,256 $ 689,573 Other liabilities 15,861 16,537 Partners' capital 297,703 297,902 Total liabilities and partners' capital $ 938,820 $ 1,004,012 The following is a combined summary of the operating results of the entities accounted for using the equity method discussed above for the periods presented (dollars in thousands): For the three months ended 3/31/2017 3/31/2016 (unaudited) Rental and other income $ 28,642 $ 36,955 Operating and other expenses (11,094 ) (14,170 ) Gain on sale of communities 29,447 103,321 Interest expense, net (1) (6,948 ) (20,001 ) Depreciation expense (7,327 ) (9,240 ) Net income $ 32,720 $ 96,865 _____________________________________ (1) Amount for the three months ended March 31, 2016 includes charges for prepayment penalties and write-offs of deferred financing costs of $10,864 . In conjunction with the formation of Fund II and North Point II JV, LP ("AVA North Point"), and the acquisition of Archstone Multifamily Partners AC LP (the "U.S. Fund"), Multifamily Partners AC JV LP (the "AC JV") and Brandywine Apartments of Maryland, LLC ("Brandywine"), the Company incurred costs in excess of its equity in the underlying net assets of the respective investments. These costs represent $37,148,000 and $38,015,000 at March 31, 2017 and December 31, 2016 , respectively, of the Company's respective investment balances. These amounts are being amortized over the lives of the underlying assets as a component of equity in income of unconsolidated entities on the accompanying Condensed Consolidated Statements of Comprehensive Income. Investments in Consolidated Real Estate Entities In conjunction with the development of Avalon Brooklyn Bay, the Company entered into a joint venture agreement to construct a mixed-use building that will contain rental apartments, for-sale residential condominium units and related common elements. The Company owns a 70.0% interest in the venture and will have all of the rights and obligations associated with the rental apartments, and the venture partner owns the remaining 30.0% interest and will have all of the rights and obligations associated with the for-sale residential condominium units. The Company is responsible for the development and construction of the structure, and is providing a loan to the venture partner for the venture partner's share of costs. As of March 31, 2017 , the Company has a receivable from the venture partner in the form of a variable rate mortgage note, secured by the for-sale residential condominium units, in the amount of $32,036,000 for outstanding principal and interest, reported as a component of prepaid expenses and other assets on the accompanying Condensed Consolidated Balance Sheets. The Company recognizes interest income on the accrual basis. The loan will be repaid by the venture partner with the proceeds the partner receives from the sales of the residential condominium units which are expected to occur during 2017 and 2018. The venture is considered a VIE, and the Company consolidates its interest in the rental apartments and common areas. Expensed Acquisition, Development and Other Pursuit Costs and Impairment of Long-Lived Assets The Company capitalizes pre-development costs incurred in pursuit of new development opportunities for which the Company currently believes future development is probable ("Development Rights"). Future development of these Development Rights is dependent upon various factors, including zoning and regulatory approval, rental market conditions, construction costs and the availability of capital. Initial pre-development costs incurred for pursuits for which future development is not yet considered probable are expensed as incurred. In addition, if the status of a Development Right changes, making future development by the Company no longer probable, any capitalized pre-development costs are expensed. The Company expensed costs related to the abandonment of Development Rights as well as costs incurred in pursuing the acquisition of assets or costs incurred pursuing the disposition of assets for which such acquisition and disposition activity did not occur, in the amounts of $728,000 and $746,000 for the three months ended March 31, 2017 and 2016 , respectively. These costs are included in expensed acquisition, development, and other pursuit costs, net of recoveries on the accompanying Condensed Consolidated Statements of Comprehensive Income. Abandoned pursuit costs can vary greatly, and the costs incurred in any given period may be significantly different in future periods. The Company evaluates its real estate and other long-lived assets for impairment when potential indicators of impairment exist. Such assets are stated at cost, less accumulated depreciation and amortization, unless the carrying amount of the asset is not recoverable. If events or circumstances indicate that the carrying amount of a property or long-lived asset may not be recoverable, the Company assesses its recoverability by comparing the carrying amount of the property or long-lived asset to its estimated undiscounted future cash flows. If the carrying amount exceeds the aggregate undiscounted future cash flows, the Company recognizes an impairment loss to the extent the carrying amount exceeds the estimated fair value of the property or long-lived asset. Based on periodic tests of recoverability of long-lived assets for the three months ended March 31, 2017 and 2016 , the Company did not recognize any impairment losses for wholly-owned operating real estate assets. The Company assesses its portfolio of land held for both development and investment for impairment if the intent of the Company changes with respect to either the development of, or the expected holding period for, the land. During the three months ended March 31, 2017 , the Company recognized an impairment charge of $9,350,000 relating to a land parcel which the Company had acquired for development in 2004 and no longer intends to develop. During the three months ended March 31, 2016 , the Company recognized an aggregate impairment charge of $6,500,000 relating to two undeveloped land parcels. These charges were determined as the excess of the Company's carrying basis over the expected sales price for each parcel, and these charges are included in casualty and impairment loss (gain), net on the accompanying Condensed Consolidated Statements of Comprehensive Income. The Company evaluates its unconsolidated investments for other than temporary impairment, considering both the extent and amount by which the carrying value of the investment exceeds the fair value, and the Company's intent and ability to hold the investment to recover its carrying value. The Company also evaluates its proportionate share of any impairment of assets held by unconsolidated investments. There were no other than temporary impairment losses recognized by any of the Company's investments in unconsolidated real estate entities during the three months ended March 31, 2017 and 2016 . Casualty Gains and Losses During the three months ended March 31, 2017, the Company recorded a casualty loss of $19,481,000 composed of a charge of $16,361,000 to write-off the net book value of the fixed assets destroyed in the Maplewood casualty loss, and demolition and additional incident expenses of $3,120,000 . The casualty loss was partially offset by $17,143,000 of expected property damage insurance proceeds, of which $4,545,000 was received during the three months ended March 31, 2017. The receivable for the remaining $12,598,000 of expected property damage insurance proceeds is included in prepaid expenses and other assets on the accompanying Condensed Consolidated Balance Sheets. The net casualty loss of $2,338,000 is included in casualty and impairment loss (gain), net on the accompanying Condensed Consolidated Statements of Comprehensive Income. See discussion in Note 1, "Organization, Basis of Presentation and Significant Accounting Policies, Legal and Other Contingencies," for further discussion of the Maplewood casualty loss. During the three months ended March 31, 2016 , the Company reached a final insurance settlement for the property damage and lost income for the Edgewater casualty loss. In 2015 and 2016, the Company received aggregate insurance proceeds for Edgewater of $73,150,000 , after self-insurance and deductibles. During the three months ended March 31, 2016 , the Company received the final $29,008,000 of insurance proceeds, of which $8,702,000 was recognized as casualty and impairment loss (gain), net on the accompanying Condensed Consolidated Statements of Comprehensive Income, and $20,306,000 as business interruption insurance proceeds, which is recorded as a component of rental and other income on the accompanying Condensed Consolidated Statements of Comprehensive Income. See discussion in Note 1, "Organization, Basis of Presentation and Significant Accounting Policies, Legal and Other Contingencies," and Part II, Item 1, "Legal Proceedings," for further discussion of the Edgewater casualty loss.

Real Estate Disposition Activit

Real Estate Disposition Activities	3 Months Ended
	Mar. 31, 2017
Discontinued Operations and Disposal Groups [Abstract]
Real Estate Disposition Activities	Real Estate Disposition Activities During the three months ended March 31, 2017 , the Company sold the following real estate assets. • Avalon Pines, located in Coram, NY, containing 450 homes, and the adjacent golf course were sold for $140,000,000 . The Company's gain in accordance with GAAP on the disposition was $87,949,000 , reported in gain on sale of communities on the accompanying Condensed Consolidated Statements of Comprehensive Income. The sale of Avalon Pines is expected to be part of a tax deferred exchange under which the Company has restricted the cash proceeds in an escrow account, classified as cash in escrow on the accompanying Condensed Consolidated Balance Sheet. • Two undeveloped land parcels, located in Newcastle, WA, that are adjacent to one of the Company's Development Communities, and 421-a tax certificates, representing the right to qualify for certain property tax exemptions in New York City, were sold for an aggregate sales price of $22,286,000 . The Company's gain in accordance with GAAP on the dispositions was $366,000 , reported in gain on sale of other real estate on the accompanying Condensed Consolidated Statements of Comprehensive Income. At March 31, 2017 , the Company had no real estate assets that qualified as held for sale.

Segment Reporting

Segment Reporting	3 Months Ended
	Mar. 31, 2017
Segment Reporting [Abstract]
Segment Reporting	Segment Reporting The Company's reportable operating segments include Established Communities, Other Stabilized Communities, and Development/Redevelopment Communities. Annually as of January 1, the Company determines which of its communities fall into each of these categories and generally maintains that classification throughout the year for the purpose of reporting segment operations, unless disposition or redevelopment plans regarding a community change. In addition, the Company owns land for future development and has other corporate assets that are not allocated to an operating segment. The Company's segment disclosures present the measure(s) used by the chief operating decision maker for purposes of assessing each segment's performance. The Company's chief operating decision maker is comprised of several members of its executive management team who use net operating income ("NOI") as the primary financial measure for Established Communities and Other Stabilized Communities. NOI is defined by the Company as total property revenue less direct property operating expenses (including property taxes), and excluding corporate-level income (including management, development and other fees), corporate-level property management and other indirect operating expenses, investments and investment management expenses, expensed acquisition, development and other pursuit costs, net of recoveries, interest expense, net, loss (gain) on extinguishment of debt, net, general and administrative expense, equity in (loss) income of unconsolidated real estate entities, depreciation expense, corporate income tax expense, casualty and impairment loss (gain), net, gain on sale of real estate assets and net operating income from real estate assets sold or held for sale. Although the Company considers NOI a useful measure of a community's or communities' operating performance, NOI should not be considered an alternative to net income or net cash flow from operating activities, as determined in accordance with GAAP. NOI excludes a number of income and expense categories as detailed in the reconciliation of NOI to net income. A reconciliation of NOI to net income for the three months ended March 31, 2017 and 2016 is as follows (dollars in thousands): For the three months ended 3/31/2017 3/31/2016 Net income $ 235,781 $ 237,877 Indirect operating expenses, net of corporate income 16,297 16,537 Investments and investment management expense 1,321 1,145 Expensed acquisition, development and other pursuit costs, net of recoveries 728 3,462 Interest expense, net 49,295 43,410 General and administrative expense 13,206 11,404 Equity in income of unconsolidated real estate entities (16,672 ) (27,969 ) Depreciation expense 140,621 127,216 Income tax expense 20 37 Casualty and impairment loss (gain), net 11,688 (2,202 ) Gain on sale of real estate (88,315 ) (51,430 ) Net operating income from real estate assets sold or held for sale (1,387 ) (8,606 ) Net operating income $ 362,583 $ 350,881 The following is a summary of NOI from real estate assets sold or held for sale for the periods presented (dollars in thousands): For the three months ended 3/31/2017 3/31/2016 Rental income from real estate assets sold or held for sale $ 2,650 $ 13,916 Operating expenses from real estate assets sold or held for sale (1,263 ) (5,310 ) Net operating income from real estate assets sold or held for sale $ 1,387 $ 8,606 The primary performance measure for communities under development or redevelopment depends on the stage of completion. While under development, management monitors actual construction costs against budgeted costs as well as lease-up pace and rent levels compared to budget. The following table provides details of the Company's segment information as of the dates specified (dollars in thousands). The segments are classified based on the individual community's status at the beginning of the given calendar year. Therefore, each year the composition of communities within each business segment is adjusted. Accordingly, the amounts between years are not directly comparable. Segment information for total revenue and NOI for the three months ended March 31, 2017 and 2016 has been adjusted to exclude the real estate assets that were sold from January 1, 2016 through March 31, 2017 , or otherwise qualify as held for sale as of March 31, 2017 , as described in Note 6, "Real Estate Disposition Activities." Segment information for gross real estate as of March 31, 2017 and 2016 has not been adjusted to exclude real estate assets that were sold or otherwise qualified as held for sale subsequent to the respective balance sheet dates. For the three months ended Total NOI % NOI change from prior year Gross real estate (1) For the three months ended March 31, 2017 Established New England $ 58,607 $ 37,816 3.3 % $ 1,875,024 Metro NY/NJ 87,544 60,060 3.8 % 2,903,317 Mid-Atlantic 55,755 39,147 3.7 % 2,062,311 Pacific Northwest 20,454 14,815 5.2 % 731,537 Northern California 83,323 63,717 2.0 % 2,815,589 Southern California 83,225 60,551 6.2 % 3,005,810 Total Established 388,908 276,106 3.9 % 13,393,588 Other Stabilized 74,021 51,571 N/A 3,032,689 Development / Redevelopment 55,547 34,906 N/A 4,276,266 Land Held for Development N/A N/A N/A 103,954 Non-allocated (3) 1,200 N/A N/A 112,987 Total $ 519,676 $ 362,583 3.3 % $ 20,919,484 For the three months ended March 31, 2016 Established New England $ 57,196 $ 36,508 15.9 % $ 1,860,863 Metro NY/NJ 83,079 56,702 3.2 % 2,883,958 Mid-Atlantic 57,530 40,063 1.3 % 2,330,106 Pacific Northwest 19,289 14,078 5.8 % 795,228 Northern California 78,452 60,248 11.5 % 2,651,741 Southern California 71,257 51,041 9.8 % 2,633,553 Total Established 366,803 258,640 7.9 % 13,155,449 Other Stabilized (2) 73,004 56,914 N/A 2,196,700 Development / Redevelopment 53,251 35,327 N/A 3,802,952 Land Held for Development N/A N/A N/A 477,072 Non-allocated (3) 1,524 N/A N/A 89,056 Total $ 494,582 $ 350,881 21.7 % $ 19,721,229 __________________________________ (1) Does not include gross real estate assets held for sale of $20,341 as of March 31, 2016 . (2) Total revenue and NOI for the three months ended March 31, 2016 includes $20,306 in business interruption insurance proceeds related to the Edgewater casualty loss. (3) Revenue represents third-party management, asset management and developer fees and miscellaneous income which are not allocated to a reportable segment.

Stock-Based Compensation Plans

Stock-Based Compensation Plans	3 Months Ended
	Mar. 31, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Stock-Based Compensation Plans	Stock-Based Compensation Plans As part of its long term compensation plans, the Company has granted stock options, performance awards and restricted stock. Detail of the outstanding awards and activity is presented below. Information with respect to stock options granted under the Company's 1994 Stock Option and Incentive Plan (the "1994 Plan") and its 2009 Stock Option and Incentive Plan (the "2009 Plan") is as follows: 2009 Plan shares Weighted average exercise price per share 1994 Plan shares Weighted average exercise price per share Options Outstanding, December 31, 2016 177,333 $ 124.25 22,541 $ 77.91 Exercised (3,085 ) 120.74 (4,181 ) 129.72 Forfeited — — — — Options Outstanding, March 31, 2017 (1) 174,248 $ 124.31 18,360 $ 66.11 __________________________________ (1) All options outstanding are exercisable as of March 31, 2017 . Information with respect to performance awards granted is as follows: Performance awards Weighted average grant date fair value per award Outstanding at December 31, 2016 251,163 $ 136.74 Granted (1) 81,708 176.59 Change in awards based on performance (2) 49,323 119.26 Converted to restricted stock (128,482 ) 118.75 Forfeited (792 ) 160.39 Outstanding at March 31, 2017 252,920 $ 155.27 __________________________________ (1) The amount of restricted stock that ultimately may be earned is based on the total shareholder return metrics related to the Company's common stock for 49,374 performance awards and financial metrics related to operating performance and leverage metrics of the Company for 32,334 performance awards. (2) Represents the change in the number of performance awards earned based on performance achievement. The Company used a Monte Carlo model to assess the compensation cost associated with the portion of the performance awards determined by using total shareholder return measures. The assumptions used are as follows: 2017 Dividend yield 3.2% Estimated volatility over the life of the plan (1) 15.3% - 19.7% Risk free rate 0.69% - 1.61% Estimated performance award value based on total shareholder return measure $175.86 __________________________________ (1) Estimated volatility over the life of the plan is using 50% historical volatility and 50% implied volatility. For the portion of the performance awards granted in 2017 , for which achievement will be determined by using financial metrics, the compensation cost was based on a weighted average grant date value of $179.07 , and the Company's estimate of corporate achievement for the financial metrics. Information with respect to restricted stock granted is as follows: Restricted stock shares Restricted stock shares weighted average grant date fair value per share Restricted stock shares converted from performance awards Outstanding at December 31, 2016 136,705 $ 158.51 176,698 Granted - restricted stock shares 70,020 179.07 128,482 Vested - restricted stock shares (65,702 ) 153.05 (69,149 ) Forfeited (236 ) 173.73 — Outstanding at March 31, 2017 140,787 $ 171.25 236,031 Total employee stock-based compensation cost recognized in income was $3,986,000 and $3,742,000 for the three months ended March 31, 2017 and 2016 , respectively, and total capitalized stock-based compensation cost was $2,078,000 and $3,048,000 for the three months ended March 31, 2017 and 2016 , respectively. At March 31, 2017 , there was a total unrecognized compensation cost of $45,637,000 for unvested restricted stock and performance awards, which does not include forfeitures, and is expected to be recognized over a weighted average period of 3.9 years.

Related Party Arrangements

Related Party Arrangements	3 Months Ended
	Mar. 31, 2017
Related Party Transactions [Abstract]
Related Party Arrangements	Related Party Arrangements Unconsolidated Entities The Company manages unconsolidated real estate entities for which it receives asset management, property management, development and redevelopment fee revenue. From these entities, the Company earned fees of $1,200,000 and $1,524,000 during the three months ended March 31, 2017 and 2016 , respectively. These fees are recognized on an accrual basis when earned in accordance with the accounting guidance applicable to revenue recognition, and are included in management, development and other fees on the accompanying Condensed Consolidated Statements of Comprehensive Income. In addition, the Company has outstanding receivables associated with its property and construction management role of $3,846,000 and $5,239,000 as of March 31, 2017 and December 31, 2016 , respectively. Director Compensation The Company recorded non-employee director compensation expense relating to restricted stock grants and deferred stock awards in the amount of $371,000 and $341,000 in the three months ended March 31, 2017 and 2016 , respectively, as a component of general and administrative expense. Deferred compensation relating to these restricted stock grants and deferred stock awards to non-employee directors was $212,000 and $531,000 on March 31, 2017 and December 31, 2016 , respectively.

Fair Value

Fair Value	3 Months Ended
	Mar. 31, 2017
Fair Value Disclosures [Abstract]
Fair Value	Fair Value Financial Instruments Carried at Fair Value Derivative Financial Instruments Currently, the Company uses interest rate swap and interest rate cap agreements to manage its interest rate risk. These instruments are carried at fair value in the Company's financial statements. In adjusting the fair value of its derivative contracts for the effect of counterparty nonperformance risk, the Company has considered the impact of its net position with a given counterparty, as well as any applicable credit enhancements, such as collateral postings, thresholds, mutual puts, and guarantees. The Company minimizes its credit risk on these transactions by dealing with major, creditworthy financial institutions which have an A or better credit rating by the Standard & Poor's Ratings Group. As part of its on-going control procedures, the Company monitors the credit ratings of counterparties and the exposure of the Company to any single entity, thus reducing credit risk concentration. The Company believes the likelihood of realizing losses from counterparty nonperformance is remote. Although the Company has determined that the majority of the inputs used to value its derivatives fall within Level 2 of the fair value hierarchy, such as interest rate, term to maturity and volatility, the credit valuation adjustments associated with its derivatives use Level 3 inputs, such as estimates of current credit spreads, to evaluate the likelihood of default by itself and its counterparties. As of March 31, 2017 , the Company assessed the significance of the impact of the credit valuation adjustments on the overall valuation of its derivative positions and has determined it is not significant. As a result, the Company has determined that its derivative valuations are classified in Level 2 of the fair value hierarchy. Hedge ineffectiveness did not have a material impact on earnings of the Company for the three months ended March 31, 2017 , or any prior period, and the Company does not anticipate that it will have a material effect in the future. The following table summarizes the consolidated derivative positions at March 31, 2017 (dollars in thousands): Non-designated Hedges Interest Rate Caps Cash Flow Hedges Interest Rate Caps Cash Flow Hedges Interest Rate Swaps Notional balance $ 696,591 $ 35,685 $ 900,000 Weighted average interest rate (1) 2.6 % 2.8 % N/A Weighted average swapped/capped interest rate 6.1 % 5.9 % 2.3 % Earliest maturity date Aug 2017 Apr 2019 Nov 2017 Latest maturity date Nov 2021 Apr 2019 May 2018 ____________________________________ (1) For interest rate caps, represents the weighted average interest rate on the hedged debt. During the three months ended March 31, 2017 , the Company entered into $100,000,000 of forward interest rate swap agreements executed to reduce the impact of variability in interest rates on a portion of the Company's expected debt issuance activity in 2018. As of March 31, 2017 , the Company has $900,000,000 in aggregate outstanding forward interest rate swap agreements. At maturity of the outstanding swap agreements, the Company expects to cash settle the contracts and either pay or receive cash for the then current fair value. Assuming that the Company issues the debt as expected, the hedging impact from these positions will then be recognized over the life of the issued debt as a yield adjustment. Excluding derivatives executed to hedge secured debt on communities classified as held for sale, the Company had 13 derivatives designated as cash flow hedges and 14 derivatives not designated as hedges at March 31, 2017 . Fair value changes for derivatives not in qualifying hedge relationships for the three months ended March 31, 2017 and 2016 were not material. During three months ended March 31, 2017 , the Company deferred $145,000 of gains for cash flow hedges reported as a component of other comprehensive income (loss). The following table summarizes the deferred losses reclassified from accumulated other comprehensive income as a component of interest expense, net (dollars in thousands): For the three months ended 3/31/2017 3/31/2016 Cash flow hedge losses reclassified to earnings $ 1,752 $ 1,374 The Company anticipates reclassifying approximately $6,975,000 of hedging losses from accumulated other comprehensive loss into earnings within the next 12 months to offset the variability of cash flows of the hedged item during this period. The Company did not have any derivatives designated as fair value hedges as of March 31, 2017 and 2016 . Redeemable Noncontrolling Interests The Company provided redemption options (the "Puts") that allow joint venture partners of the Company to require the Company to purchase their interests in the investment at a guaranteed minimum amount related to three ventures. The Puts are payable in cash. The Company determines the fair value of the Puts based on unobservable inputs considering the assumptions that market participants would make in pricing the obligations, applying a guaranteed rate of return to the joint venture partners' net capital contribution balances as of period end. Given the significance of the unobservable inputs, the valuations are classified in Level 3 of the fair value hierarchy. The Company issued units of limited partnership interest in DownREITs which provide the DownREIT limited partners the ability to present all or some of their units for redemption for cash as determined by the partnership agreement. Under the DownREIT agreements, for each limited partnership unit, the limited partner is entitled to receive cash in the amount equal to the fair value of the Company's common stock on or about the date of redemption. In lieu of cash redemption, the Company may elect to exchange such units for an equal number of shares of the Company's common stock. The limited partnership units in the DownREITs are valued using the market price of the Company's common stock, a Level 1 price under the fair value hierarchy. Financial Instruments Not Carried at Fair Value Cash and Cash Equivalents Cash and cash equivalent balances are held with various financial institutions within principal protected accounts. The Company monitors credit ratings of these financial institutions and the concentration of cash and cash equivalent balances with any one financial institution and believes the likelihood of realizing material losses related to cash and cash equivalent balances is remote. Cash and cash equivalents are carried at their face amounts, which reasonably approximate their fair values and are Level 1 within the fair value hierarchy. Other Financial Instruments Rents and other receivables and prepaids, accounts and construction payable and accrued expenses and other liabilities are carried at their face amounts, which reasonably approximate their fair values. The Company values its unsecured notes using quoted market prices, a Level 1 price within the fair value hierarchy. The Company values its notes payable and outstanding amounts under the Credit Facility and Term Loan using a discounted cash flow analysis on the expected cash flows of each instrument. This analysis reflects the contractual terms of the instrument, including the period to maturity, and uses observable market-based inputs, including interest rate curves. The process also considers credit valuation adjustments to appropriately reflect the Company's nonperformance risk. The Company has concluded that the value of its notes payable and amounts outstanding under its Credit Facility and Term Loan are Level 2 prices as the majority of the inputs used to value its positions fall within Level 2 of the fair value hierarchy. Financial Instruments Measured/Disclosed at Fair Value on a Recurring Basis The following tables summarize the classification between the three levels of the fair value hierarchy of the Company's financial instruments measured/disclosed at fair value on a recurring basis (dollars in thousands): Description Total Fair Value Quoted Prices (Level 1) Significant (Level 2) Significant (Level 3) 3/31/2017 Non-Designated Hedges Interest Rate Caps $ 30 $ — $ 30 $ — Cash Flow Hedges Interest Rate Swaps - Assets 14,955 — 14,955 — Interest Rate Swaps - Liabilities (102 ) — (102 ) — Puts (5,928 ) — — (5,928 ) DownREIT units (1,377 ) (1,377 ) — — Indebtedness Unsecured notes (4,226,278 ) (4,226,278 ) — — Mortgage notes payable and unsecured term loan (2,743,794 ) — (2,743,794 ) — Total $ (6,962,494 ) $ (4,227,655 ) $ (2,728,911 ) $ (5,928 ) Description Total Fair Value Quoted Prices (Level 1) Significant (Level 2) Significant (Level 3) 12/31/2016 Non-Designated Hedges Interest Rate Caps $ 79 $ — $ 79 $ — Cash Flow Hedges Interest Rate Caps 2 — 2 — Interest Rate Swaps - Assets 14,775 — 14,775 — Puts (6,002 ) — — (6,002 ) DownREIT units (1,329 ) (1,329 ) — — Indebtedness Unsecured notes (4,218,627 ) (4,218,627 ) — — Mortgage notes payable and unsecured term loan (2,744,462 ) — (2,744,462 ) — Total $ (6,955,564 ) $ (4,219,956 ) $ (2,729,606 ) $ (6,002 )

Subsequent Events

Subsequent Events	3 Months Ended
	Mar. 31, 2017
Subsequent Events [Abstract]
Subsequent Events	Subsequent Events The Company has evaluated subsequent events through the date on which this Form 10-Q was filed, the date on which these financial statements were issued, and identified the items below for discussion. In April 2017, the Company borrowed the $250,000,000 available under the $250 million Term Loan discussed in Note 3, "Mortgage Notes Payable, Unsecured Notes and Credit Facility." In May 2017, the Company repaid $498,357,000 of fixed rate mortgage notes with an effective interest rate of 3.36% , secured by eight communities at par in advance of their November 2017 maturity dates. As of May 2, 2017, the Company has $395,000,000 outstanding under the Credit Facility.

Organization, Basis of Presen18

Organization, Basis of Presentation and Significant Accounting Policies (Policies)	3 Months Ended
	Mar. 31, 2017
Accounting Policies [Abstract]
Organization and Basis of Presentation	Organization and Basis of Presentation AvalonBay Communities, Inc. (the "Company," which term, unless the context otherwise requires, refers to AvalonBay Communities, Inc. together with its subsidiaries), is a Maryland corporation that has elected to be treated as a real estate investment trust ("REIT") for federal income tax purposes under the Internal Revenue Code of 1986 (the "Code"). The Company focuses on the development, redevelopment, acquisition, ownership and operation of multifamily communities primarily in New England, the New York/New Jersey metro area, the Mid-Atlantic, the Pacific Northwest, and Northern and Southern California. At March 31, 2017 , the Company owned or held a direct or indirect ownership interest in 260 operating apartment communities containing 74,952 apartment homes in 10 states and the District of Columbia, of which nine communities containing 4,075 apartment homes were under redevelopment. In addition, the Company owned or held a direct or indirect ownership interest in 24 communities under development that are expected to contain an aggregate of 7,581 apartment homes when completed. The Company also owned or held a direct or indirect ownership interest in land or rights to land on which the Company expects to develop an additional 28 communities that, if developed as expected, will contain an estimated 9,304 apartment homes. The interim unaudited financial statements have been prepared in accordance with U.S. generally accepted accounting principles ("GAAP") for interim financial information and in conjunction with the rules and regulations of the Securities and Exchange Commission ("SEC"). Certain information and footnote disclosures normally included in financial statements required by GAAP have been condensed or omitted pursuant to such rules and regulations. These unaudited financial statements should be read in conjunction with the financial statements and notes included in the Company's 2016 Annual Report on Form 10-K. The results of operations for the three months ended March 31, 2017 are not necessarily indicative of the operating results for the full year. Management believes the disclosures are adequate to ensure the information presented is not misleading. In the opinion of management, all adjustments and eliminations, consisting only of normal, recurring adjustments necessary for a fair presentation of the financial statements for the interim periods, have been included. Capitalized terms used without definition have meanings provided elsewhere in this Form 10-Q.
Earnings per Common Share	Earnings per Common Share Basic earnings per share is computed by dividing net income attributable to common stockholders by the weighted average number of shares outstanding during the period. All outstanding unvested restricted share awards contain rights to non-forfeitable dividends and participate in undistributed earnings with common shareholders and, accordingly, are considered participating securities that are included in the two-class method of computing basic earnings per share ("EPS"). Both the unvested restricted shares and other potentially dilutive common shares, and the related impact to earnings, are considered when calculating earnings per share on a diluted basis. The Company's earnings per common share are determined as follows (dollars in thousands, except per share data): For the three months ended 3/31/2017 3/31/2016 Basic and diluted shares outstanding Weighted average common shares - basic 137,068,874 136,785,880 Weighted average DownREIT units outstanding 7,500 7,500 Effect of dilutive securities 454,868 589,664 Weighted average common shares - diluted 137,531,242 137,383,044 Calculation of Earnings per Share - basic Net income attributable to common stockholders $ 235,875 $ 237,931 Net income allocated to unvested restricted shares (652 ) (632 ) Net income attributable to common stockholders, adjusted $ 235,223 $ 237,299 Weighted average common shares - basic 137,068,874 136,785,880 Earnings per common share - basic $ 1.72 $ 1.73 Calculation of Earnings per Share - diluted Net income attributable to common stockholders $ 235,875 $ 237,931 Add: noncontrolling interests of DownREIT unitholders in consolidated partnerships 11 10 Adjusted net income attributable to common stockholders $ 235,886 $ 237,941 Weighted average common shares - diluted 137,531,242 137,383,044 Earnings per common share - diluted $ 1.72 $ 1.73 All options to purchase shares of common stock outstanding as of March 31, 2017 and 2016 are included in the computation of diluted earnings per share. As discussed under "Recently Issued and Adopted Accounting Standards," as of January 1, 2017, the Company adopted the provision of ASU 2016-09 using the modified retrospective approach to recognize forfeitures as they occur. Prior to the adoption of this standard, the Company was required to estimate the forfeiture of stock options and recognized compensation cost net of the estimated forfeitures. The estimated forfeitures included in compensation cost were adjusted to reflect actual forfeitures at the end of the vesting period. The change in accounting principle had an immaterial effect on the Company's financial position and no adjustment to retained earnings or the Company's diluted shares outstanding, as prescribed under the modified retrospective approach, was required in the prior year period.
Derivative Instruments and Hedging Activities	Derivative Instruments and Hedging Activities The Company enters into interest rate swap and interest rate cap agreements (collectively, "Hedging Derivatives") for interest rate risk management purposes and in conjunction with certain variable rate secured debt to satisfy lender requirements. The Company does not enter into Hedging Derivative transactions for trading or other speculative purposes. The Company assesses the effectiveness of qualifying cash flow and fair value hedges, both at inception and on an on-going basis. Hedge ineffectiveness is reported as a component of general and administrative expenses. The fair values of Hedging Derivatives that are in an asset position are recorded in prepaid expenses and other assets. The fair value of Hedging Derivatives that are in a liability position are included in accrued expenses and other liabilities. The Company does not present or disclose the fair value of Hedging Derivatives on a net basis. Fair value changes for derivatives that are not in qualifying hedge relationships are reported as a component of interest expense, net. For the Hedging Derivative positions that the Company has determined qualify as effective cash flow hedges, the Company has recorded the effective portion of cumulative changes in the fair value of Hedging Derivatives in other comprehensive income (loss). Amounts recorded in other comprehensive income (loss) will be reclassified into earnings in the periods in which earnings are affected by the hedged cash flow. The effective portion of the change in fair value of the Hedging Derivatives that the Company has determined qualified as effective fair value hedges is reported as an adjustment to the carrying amount of the corresponding debt being hedged.
Legal and Other Contingencies	Legal and Other Contingencies Maplewood Casualty Loss In February 2017, a fire occurred at the Company's Avalon Maplewood Development Community, located in Maplewood, NJ, which was under construction and not yet occupied. The Company believes that liabilities to third parties resulting from the fire will not be material and will, in any event, be substantially covered by insurance subject to a deductible. The Company has commenced reconstruction of the damaged and destroyed portions of the community. See Note 5, "Investments in Real Estate Entities," for further discussion of the casualty gains and losses associated with the Maplewood casualty loss. Edgewater Casualty Loss In January 2015, a fire occurred at the Company's Avalon at Edgewater apartment community located in Edgewater, New Jersey ("Edgewater"). Edgewater consisted of two residential buildings. One building, containing 240 apartment homes, was destroyed. The second building, containing 168 apartment homes, suffered minimal damage and has been repaired. The Company has established protocols for processing claims from third parties who suffered losses as a result of the fire, and many third parties have contacted the Company's insurance carrier and settled their claims. See Part II, Item 1, "Legal Proceedings," for further discussion of the lawsuits associated with the Edgewater casualty loss. Three class action lawsuits have been filed against the Company on behalf of occupants of the destroyed building and consolidated in the United States District Court for the District of New Jersey. The Company has agreed with class counsel to the terms of a proposed settlement which would provide a claims process (with agreed upon protocols for instructing the adjuster as to how to evaluate claims) and, if needed, an arbitration process to determine damage amounts to be paid to individual claimants covered by the class settlement. In March 2017 the District Court granted preliminary approval of the class action settlement and in July 2017 a fairness hearing will be held to determine whether the settlement will receive final approval. A fourth class action, being heard in the same federal court, was filed against the Company on behalf of residents of the second Edgewater building that suffered minimal damage. Recently, a fifth class action lawsuit was filed against the Company seeking to certify a class on behalf of both buildings and other third parties. That action is currently stayed pending the decision by those plaintiffs either to be included in the class settlement or to formally opt-out. In addition to the class action lawsuits described above, 19 lawsuits representing approximately 146 individual plaintiffs have been filed and are currently pending in the Superior Court of New Jersey Bergen County - Law Division. All of these state court cases have been consolidated by the court. These plaintiffs, if eligible to be class members under the class settlement that has been preliminarily approved as described above, must formally opt-out of that class action settlement by May 17, 2017 if they want to continue their individual actions. The Company believes that it has meritorious defenses to the extent of damages claimed in all of the suits. There are also five subrogation lawsuits that have been filed against the Company by insurers of Edgewater residents who obtained renters insurance; it is the Company's position that in the majority of the applicable leases the residents waived subrogation rights. One of these lawsuits has been dismissed on that basis and the other four are currently pending in the United States District Court for the District of New Jersey. The District Court recently denied the Company's motions seeking dismissal on this basis. The Company will reassess the viability of this defense after conducting additional discovery. Having settled many third party claims through the insurance claims process, the Company currently believes that any potential remaining liability to third parties (including any potential liability to third parties determined in accordance with the class settlement described above, if approved) will not be material to the Company and will in any event be substantially covered by the Company's insurance policies. However, the Company can give no assurances in this regard and continues to evaluate this matter. See Note 5, "Investments in Real Estate Entities," and Part II, Item 1, "Legal Proceedings," for further discussion of the casualty gains and losses and lawsuits associated with the Edgewater casualty loss. Other Matters The Company is involved in various other claims and/or administrative proceedings unrelated to the Edgewater casualty loss that arise in the ordinary course of its business. While no assurances can be given, the Company does not currently believe that any of these other outstanding litigation matters, individually or in the aggregate, will have a material adverse effect on its financial condition or results of operations.
Real Estate, Policy	Acquisitions of Investments in Real Estate The Company accounts for acquisitions of investments in real estate in accordance with the authoritative guidance for the initial measurement, which requires the identifiable assets acquired, the liabilities assumed and any noncontrolling interest in the acquiree to be recognized at fair value. Typical assets and liabilities acquired include land, building, furniture, fixtures and equipment, debt and identified intangible assets and liabilities, consisting of the value of above or below market leases and in-place leases. In making estimates of fair values for purposes of allocating purchase price, the Company utilizes various sources, including its own analysis of recently acquired and existing comparable properties in its portfolio and other market data. Consideration for acquisitions is typically in the form of cash unless otherwise disclosed. For an acquisition of a business, the allocation of the purchase price is based on the fair value of the net assets, and for an asset acquisition, the allocation of the purchase price is based on the relative fair value of the net assets. Subsequent to the adoption of ASU 2017-01 on October 1, 2016, the Company expects that acquisitions of individual operating communities will generally be viewed as asset acquisitions.
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make certain estimates and assumptions. These estimates and assumptions affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the dates of the financial statements and the reported amounts of revenue and expenses during the reporting periods. Actual results could differ from those estimates.
Reclassifications	Reclassifications Certain reclassifications have been made to amounts in prior years' notes to financial statements to conform to current year presentations as a result of changes in held for sale classification and disposition activity.
Recently Adopted Accounting Standards	Recently Issued Accounting Standards In February 2017, the Financial Accounting Standards Board ("FASB") issued Accounting Standards Update ("ASU") 2017-05, Other Income-Gains and Losses from the Derecognition of Nonfinancial Assets (Subtopic 610-20): Clarifying the Scope of Asset Derecognition Guidance and Accounting for Partial Sales of Nonfinancial Assets. This ASU clarifies the scope of the nonfinancial asset guidance and the derecognition of all businesses and nonprofit activities (except those related to conveyances of oil and gas mineral rights or contracts with customers). In addition, the amendments eliminate the exception in the financial asset guidance for transfers of investments (including equity method investments) in real estate entities and supersede the guidance in the Exchanges of a Nonfinancial Asset for a Noncontrolling Ownership Interest. The amendments also provide guidance on the accounting of partial sales of nonfinancial assets and contributions of nonfinancial assets to a joint venture or other noncontrolled investee. The new standard allows for either a retrospective or modified retrospective approach. The guidance will be effective in the first quarter of 2018 and allows for early adoption. The Company is assessing whether the new standard will have a material effect on its financial position or results of operations. In August 2016, the FASB issued ASU 2016-15, Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments. This ASU addresses eight specific cash flow issues including debt prepayment or debt extinguishment costs, proceeds from the settlement of insurance claims, distributions received from equity method investees and separately identifiable cash flows and application of the predominance principle. The new standard requires a retrospective approach. The guidance will be effective in the first quarter of 2018 and allows for early adoption. The Company adopted this guidance as of January 1, 2017. The new standard did not have a material effect on the Company's Condensed Consolidated Statements of Cash Flows. In March 2016, the FASB issued ASU 2016-09, Compensation-Stock Compensation: Improvements to Employee Share-Based Payment Accounting, which simplifies several aspects of share-based payment transactions, including income tax consequences, classification of awards as equity or liability, statement of cash flows classification and policy election options for forfeitures. Upon adoption of the standard, the Company elected to account for forfeitures when they occur instead of estimating the forfeitures. The Company adopted this guidance as of January 1, 2017, using the modified retrospective approach. The new standard did not have a material effect on the Company's financial position, results of operations or earnings per share as discussed in "Earnings per Common Share." In February 2016, the FASB issued ASU 2016-02, Leases, amending the existing accounting standards for lease accounting, including requiring lessees to recognize most leases on their balance sheets and making targeted changes to lessor accounting. The guidance will be effective in the first quarter of 2019 and allows for early adoption. The new standard requires a modified retrospective transition approach for all leases existing at, or entered into after, the date of initial application, with an option to use certain transition relief. ASU 2016-02 provides for transition relief, which includes not electing to (i) reassess whether any expired or existing contract is a lease or contains a lease, (ii) reassess the lease classification of any expired or existing leases and (iii) expense any capitalized initial direct costs for any existing leases. The Company anticipates adoption of the standard to have a material impact on its financial position and results of operations resulting from the recognition of the right to use asset and corresponding lease obligation for its long-term ground leases, currently accounted for as operating leases. The Company will continue to assess the impact of the new standard. In May 2014, the FASB issued ASU 2014-09, Revenue from Contracts with Customers and in August 2015, the FASB issued ASU 2015-14, Revenue from Contracts with Customers-Deferral of the Effective Date, which defers the effective date of the new revenue recognition standard until the first quarter of 2018. Subsequently, the FASB has issued multiple ASUs clarifying ASU 2014-09 and ASU 2015-14. Under the new standard, revenue is recognized when persuasive evidence of an arrangement exists, delivery has occurred, the fee is fixed or determinable, and collectability is probable. Revenue is generally recognized net of allowances and any taxes collected from customers and subsequently remitted to governmental authorities. The majority of the Company's revenue is derived from rental income, which is scoped out from this standard and will be accounted for under ASU 2016-02, Leases, discussed above. The Company's other revenue streams, which are being evaluated under this ASU, include but are not limited to management fees, other income from residents determined not to be within the scope of ASU 2016-02 and gains and losses from real estate dispositions. The Company will continue to assess the impact of the new standard and anticipates adoption as of January 1, 2018 using the modified retrospective approach.

Organization, Basis of Presen19

Organization, Basis of Presentation and Significant Accounting Policies (Tables)	3 Months Ended
	Mar. 31, 2017
Accounting Policies [Abstract]
Schedule of earnings per common share	The Company's earnings per common share are determined as follows (dollars in thousands, except per share data): For the three months ended 3/31/2017 3/31/2016 Basic and diluted shares outstanding Weighted average common shares - basic 137,068,874 136,785,880 Weighted average DownREIT units outstanding 7,500 7,500 Effect of dilutive securities 454,868 589,664 Weighted average common shares - diluted 137,531,242 137,383,044 Calculation of Earnings per Share - basic Net income attributable to common stockholders $ 235,875 $ 237,931 Net income allocated to unvested restricted shares (652 ) (632 ) Net income attributable to common stockholders, adjusted $ 235,223 $ 237,299 Weighted average common shares - basic 137,068,874 136,785,880 Earnings per common share - basic $ 1.72 $ 1.73 Calculation of Earnings per Share - diluted Net income attributable to common stockholders $ 235,875 $ 237,931 Add: noncontrolling interests of DownREIT unitholders in consolidated partnerships 11 10 Adjusted net income attributable to common stockholders $ 235,886 $ 237,941 Weighted average common shares - diluted 137,531,242 137,383,044 Earnings per common share - diluted $ 1.72 $ 1.73

Mortgage Notes Payable, Unsec20

Mortgage Notes Payable, Unsecured Notes and Credit Facility (Tables)	3 Months Ended
	Mar. 31, 2017
Debt Disclosure [Abstract]
Summary of company's mortgage notes payable, unsecured notes and Credit Facility excluding mortgage notes secured by communities classified as held for sale	The following amounts and discussion do not include the mortgage notes related to the communities classified as held for sale, if any, as of March 31, 2017 and December 31, 2016 , as shown in the accompanying Condensed Consolidated Balance Sheets (dollars in thousands) (see Note 6, "Real Estate Disposition Activities"). 3/31/2017 12/31/2016 Fixed rate unsecured notes (1) $ 4,200,000 $ 4,200,000 Term Loans (1) 300,000 300,000 Fixed rate mortgage notes payable - conventional and tax-exempt (2) 1,664,650 1,668,496 Variable rate mortgage notes payable - conventional and tax-exempt (2) 890,202 908,262 Total mortgage notes payable and unsecured notes 7,054,852 7,076,758 Credit Facility — — Total mortgage notes payable, unsecured notes and Credit Facility $ 7,054,852 $ 7,076,758 _____________________________________ (1) Balances at March 31, 2017 and December 31, 2016 exclude $8,640 and $8,930 , respectively, of debt discount, and $26,814 and $27,768 , respectively, of deferred financing costs, as reflected in unsecured notes, net on the accompanying Condensed Consolidated Balance Sheets. (2) Balances at March 31, 2017 and December 31, 2016 exclude $3,044 of debt discount and $1,866 of debt premium, respectively, and $10,625 and $11,046 , respectively, of deferred financing costs, as reflected in mortgage notes payable on the accompanying Condensed Consolidated Balance Sheets.
Scheduled payments and maturities of mortgage notes payable and unsecured notes outstanding	Scheduled payments and maturities of mortgage notes payable and unsecured notes outstanding at March 31, 2017 are as follows (dollars in thousands): Year Secured notes payments Secured notes maturities Unsecured notes maturities Stated interest rate of unsecured notes 2017 13,954 692,191 — N/A 2018 17,789 76,667 — N/A 2019 4,696 655,514 — N/A 2020 3,624 118,729 250,000 6.100 % 400,000 3.625 % 2021 3,551 27,844 250,000 3.950 % 300,000 LIBOR + 1.450% 2022 3,795 — 450,000 2.950 % 2023 4,040 — 350,000 4.200 % 250,000 2.850 % 2024 4,310 — 300,000 3.500 % 2025 4,585 84,835 525,000 3.450 % 300,000 3.500 % 2026 4,894 — 475,000 2.950 % 300,000 2.900 % Thereafter 213,754 620,080 350,000 3.900 % $ 278,992 $ 2,275,860 $ 4,500,000

Equity (Tables)

Equity (Tables)	3 Months Ended
	Mar. 31, 2017
Stockholders' Equity Note [Abstract]
Summary of changes in equity	The following summarizes the changes in equity for the three months ended March 31, 2017 (dollars in thousands): Common stock Additional paid-in capital Accumulated earnings less dividends Accumulated other comprehensive loss Total equity Balance at December 31, 2016 $ 1,373 $ 10,105,654 $ 94,899 $ (30,510 ) $ 10,171,416 Net income attributable to common stockholders — — 235,875 — 235,875 Gain on cash flow hedges, net — — — 145 145 Cash flow hedge loss reclassified to earnings — — — 1,752 1,752 Change in redemption value of redeemable noncontrolling interest — — (183 ) — (183 ) Dividends declared to common stockholders — — (195,657 ) — (195,657 ) Issuance of common stock, net of withholdings 5 47,962 (1,260 ) — 46,707 Amortization of deferred compensation — 6,567 — — 6,567 Balance at March 31, 2017 $ 1,378 $ 10,160,183 $ 133,674 $ (28,613 ) $ 10,266,622

Investments in Real Estate En22

Investments in Real Estate Entities (Tables)	3 Months Ended
	Mar. 31, 2017
Equity Method Investments and Joint Ventures [Abstract]
Combined summary of the financial position of the entities accounted for using the equity method	The following is a combined summary of the financial position of the entities accounted for using the equity method discussed above as of the dates presented (dollars in thousands): 3/31/2017 12/31/2016 (unaudited) (unaudited) Assets: Real estate, net $ 862,612 $ 954,493 Other assets 76,208 49,519 Total assets $ 938,820 $ 1,004,012 Liabilities and partners' capital: Mortgage notes payable, net and credit facility $ 625,256 $ 689,573 Other liabilities 15,861 16,537 Partners' capital 297,703 297,902 Total liabilities and partners' capital $ 938,820 $ 1,004,012
Combined summary of the operating results of the entities accounted for using the equity method	The following is a combined summary of the operating results of the entities accounted for using the equity method discussed above for the periods presented (dollars in thousands): For the three months ended 3/31/2017 3/31/2016 (unaudited) Rental and other income $ 28,642 $ 36,955 Operating and other expenses (11,094 ) (14,170 ) Gain on sale of communities 29,447 103,321 Interest expense, net (1) (6,948 ) (20,001 ) Depreciation expense (7,327 ) (9,240 ) Net income $ 32,720 $ 96,865 _____________________________________ (1) Amount for the three months ended March 31, 2016 includes charges for prepayment penalties and write-offs of deferred financing costs of $10,864 .

Segment Reporting (Tables)

Segment Reporting (Tables)	3 Months Ended
	Mar. 31, 2017
Segment Reporting [Abstract]
Schedule of reconciliation of NOI to net income	A reconciliation of NOI to net income for the three months ended March 31, 2017 and 2016 is as follows (dollars in thousands): For the three months ended 3/31/2017 3/31/2016 Net income $ 235,781 $ 237,877 Indirect operating expenses, net of corporate income 16,297 16,537 Investments and investment management expense 1,321 1,145 Expensed acquisition, development and other pursuit costs, net of recoveries 728 3,462 Interest expense, net 49,295 43,410 General and administrative expense 13,206 11,404 Equity in income of unconsolidated real estate entities (16,672 ) (27,969 ) Depreciation expense 140,621 127,216 Income tax expense 20 37 Casualty and impairment loss (gain), net 11,688 (2,202 ) Gain on sale of real estate (88,315 ) (51,430 ) Net operating income from real estate assets sold or held for sale (1,387 ) (8,606 ) Net operating income $ 362,583 $ 350,881
Schedule of net operating income from real estate assets sold or held for sale, not classified as discontinued operations	The following is a summary of NOI from real estate assets sold or held for sale for the periods presented (dollars in thousands): For the three months ended 3/31/2017 3/31/2016 Rental income from real estate assets sold or held for sale $ 2,650 $ 13,916 Operating expenses from real estate assets sold or held for sale (1,263 ) (5,310 ) Net operating income from real estate assets sold or held for sale $ 1,387 $ 8,606
Schedule of details of segment information	For the three months ended Total NOI % NOI change from prior year Gross real estate (1) For the three months ended March 31, 2017 Established New England $ 58,607 $ 37,816 3.3 % $ 1,875,024 Metro NY/NJ 87,544 60,060 3.8 % 2,903,317 Mid-Atlantic 55,755 39,147 3.7 % 2,062,311 Pacific Northwest 20,454 14,815 5.2 % 731,537 Northern California 83,323 63,717 2.0 % 2,815,589 Southern California 83,225 60,551 6.2 % 3,005,810 Total Established 388,908 276,106 3.9 % 13,393,588 Other Stabilized 74,021 51,571 N/A 3,032,689 Development / Redevelopment 55,547 34,906 N/A 4,276,266 Land Held for Development N/A N/A N/A 103,954 Non-allocated (3) 1,200 N/A N/A 112,987 Total $ 519,676 $ 362,583 3.3 % $ 20,919,484 For the three months ended March 31, 2016 Established New England $ 57,196 $ 36,508 15.9 % $ 1,860,863 Metro NY/NJ 83,079 56,702 3.2 % 2,883,958 Mid-Atlantic 57,530 40,063 1.3 % 2,330,106 Pacific Northwest 19,289 14,078 5.8 % 795,228 Northern California 78,452 60,248 11.5 % 2,651,741 Southern California 71,257 51,041 9.8 % 2,633,553 Total Established 366,803 258,640 7.9 % 13,155,449 Other Stabilized (2) 73,004 56,914 N/A 2,196,700 Development / Redevelopment 53,251 35,327 N/A 3,802,952 Land Held for Development N/A N/A N/A 477,072 Non-allocated (3) 1,524 N/A N/A 89,056 Total $ 494,582 $ 350,881 21.7 % $ 19,721,229 __________________________________ (1) Does not include gross real estate assets held for sale of $20,341 as of March 31, 2016 . (2) Total revenue and NOI for the three months ended March 31, 2016 includes $20,306 in business interruption insurance proceeds related to the Edgewater casualty loss. (3) Revenue represents third-party management, asset management and developer fees and miscellaneous income which are not allocated to a reportable segment.

Stock-Based Compensation Plans

Stock-Based Compensation Plans (Tables)	3 Months Ended
	Mar. 31, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Schedule of information with respect to stock options granted	Information with respect to stock options granted under the Company's 1994 Stock Option and Incentive Plan (the "1994 Plan") and its 2009 Stock Option and Incentive Plan (the "2009 Plan") is as follows: 2009 Plan shares Weighted average exercise price per share 1994 Plan shares Weighted average exercise price per share Options Outstanding, December 31, 2016 177,333 $ 124.25 22,541 $ 77.91 Exercised (3,085 ) 120.74 (4,181 ) 129.72 Forfeited — — — — Options Outstanding, March 31, 2017 (1) 174,248 $ 124.31 18,360 $ 66.11
Schedule of nonvested performance awards granted	Information with respect to performance awards granted is as follows: Performance awards Weighted average grant date fair value per award Outstanding at December 31, 2016 251,163 $ 136.74 Granted (1) 81,708 176.59 Change in awards based on performance (2) 49,323 119.26 Converted to restricted stock (128,482 ) 118.75 Forfeited (792 ) 160.39 Outstanding at March 31, 2017 252,920 $ 155.27 __________________________________ (1) The amount of restricted stock that ultimately may be earned is based on the total shareholder return metrics related to the Company's common stock for 49,374 performance awards and financial metrics related to operating performance and leverage metrics of the Company for 32,334 performance awards. (2) Represents the change in the number of performance awards earned based on performance achievement.
Summary of valuation options	The Company used a Monte Carlo model to assess the compensation cost associated with the portion of the performance awards determined by using total shareholder return measures. The assumptions used are as follows: 2017 Dividend yield 3.2% Estimated volatility over the life of the plan (1) 15.3% - 19.7% Risk free rate 0.69% - 1.61% Estimated performance award value based on total shareholder return measure $175.86 __________________________________ (1) Estimated volatility over the life of the plan is using 50% historical volatility and 50% implied volatility.
Schedule of restricted stock granted	Information with respect to restricted stock granted is as follows: Restricted stock shares Restricted stock shares weighted average grant date fair value per share Restricted stock shares converted from performance awards Outstanding at December 31, 2016 136,705 $ 158.51 176,698 Granted - restricted stock shares 70,020 179.07 128,482 Vested - restricted stock shares (65,702 ) 153.05 (69,149 ) Forfeited (236 ) 173.73 — Outstanding at March 31, 2017 140,787 $ 171.25 236,031

Fair Value (Tables)

Fair Value (Tables)	3 Months Ended
	Mar. 31, 2017
Fair Value Disclosures [Abstract]
Schedule of summary of consolidated Hedging Derivatives, excluding derivatives executed to hedge debt on communities classified as held for sale	The following table summarizes the consolidated derivative positions at March 31, 2017 (dollars in thousands): Non-designated Hedges Interest Rate Caps Cash Flow Hedges Interest Rate Caps Cash Flow Hedges Interest Rate Swaps Notional balance $ 696,591 $ 35,685 $ 900,000 Weighted average interest rate (1) 2.6 % 2.8 % N/A Weighted average swapped/capped interest rate 6.1 % 5.9 % 2.3 % Earliest maturity date Aug 2017 Apr 2019 Nov 2017 Latest maturity date Nov 2021 Apr 2019 May 2018 ____________________________________ (1) For interest rate caps, represents the weighted average interest rate on the hedged debt.
Schedule of Cash Flow Hedges Included in Accumulated Other Comprehensive Income (Loss) [Table Text Block]	For the three months ended 3/31/2017 3/31/2016 Cash flow hedge losses reclassified to earnings $ 1,752 $ 1,374
Schedule of summary of classification between the three levels of the fair value hierarchy of the Company's financial instruments measured at fair value on a recurring basis	The following tables summarize the classification between the three levels of the fair value hierarchy of the Company's financial instruments measured/disclosed at fair value on a recurring basis (dollars in thousands): Description Total Fair Value Quoted Prices (Level 1) Significant (Level 2) Significant (Level 3) 3/31/2017 Non-Designated Hedges Interest Rate Caps $ 30 $ — $ 30 $ — Cash Flow Hedges Interest Rate Swaps - Assets 14,955 — 14,955 — Interest Rate Swaps - Liabilities (102 ) — (102 ) — Puts (5,928 ) — — (5,928 ) DownREIT units (1,377 ) (1,377 ) — — Indebtedness Unsecured notes (4,226,278 ) (4,226,278 ) — — Mortgage notes payable and unsecured term loan (2,743,794 ) — (2,743,794 ) — Total $ (6,962,494 ) $ (4,227,655 ) $ (2,728,911 ) $ (5,928 ) Description Total Fair Value Quoted Prices (Level 1) Significant (Level 2) Significant (Level 3) 12/31/2016 Non-Designated Hedges Interest Rate Caps $ 79 $ — $ 79 $ — Cash Flow Hedges Interest Rate Caps 2 — 2 — Interest Rate Swaps - Assets 14,775 — 14,775 — Puts (6,002 ) — — (6,002 ) DownREIT units (1,329 ) (1,329 ) — — Indebtedness Unsecured notes (4,218,627 ) (4,218,627 ) — — Mortgage notes payable and unsecured term loan (2,744,462 ) — (2,744,462 ) — Total $ (6,955,564 ) $ (4,219,956 ) $ (2,729,606 ) $ (6,002 )

Organization, Basis of Presen26

Organization, Basis of Presentation and Significant Accounting Policies (Details)	Mar. 31, 2017statecommunityhome
Organization and Basis of Presentation
Number of operating apartment communities | community	260
Number of apartment homes included in operating apartment communities owned | home	74,952
Number of states where operating apartment communities owned are located | state	10
Number of communities with apartments under reconstruction | community	9
Number of apartment homes under reconstruction | home	4,075
Number of owned communities under construction | community	24
Expected number of apartment homes under construction | home	7,581
Communities under development rights | community	28
Estimated number of apartment homes in communities to be developed | home	9,304

Organization, Basis of Presen27

Organization, Basis of Presentation and Significant Accounting Policies (Details 2) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2017USD ($)communityClaimhomeplaintiffbuilding$ / sharesshares	Mar. 31, 2016USD ($)$ / sharesshares
Basic and diluted shares outstanding
Weighted average common shares - basic (in shares) | shares	137,068,874	136,785,880
Weighted average DownREIT units outstanding (in shares) | shares	7,500	7,500
Effect of dilutive securities (in shares) | shares	454,868	589,664
Weighted average common shares - diluted (in shares) | shares	137,531,242	137,383,044
Calculation of Earnings per Share - basic
Net income attributable to common stockholders | $	$ 235,875	$ 237,931
Net income allocated to unvested restricted shares | $	(652)	(632)
Net income attributable to common stockholders, adjusted | $	$ 235,223	$ 237,299
Weighted average common shares - basic (in shares) | shares	137,068,874	136,785,880
Earnings per common share - basic (in dollars per share) | $ / shares	$ 1.72	$ 1.73
Calculation of Earnings per Share - diluted
Net income attributable to common stockholders | $	$ 235,875	$ 237,931
Add: noncontrolling interests of DownREIT unitholders in consolidated partnerships | $	11	10
Adjusted net income attributable to common stockholders | $	$ 235,886	$ 237,941
Weighted average common shares - diluted (in shares) | shares	137,531,242	137,383,044
Earnings per common share - diluted (in dollars per share) | $ / shares	$ 1.72	$ 1.73
Loss Contingencies [Line Items]
Number of operating apartment communities | community	260
Number of apartment homes included in operating apartment communities owned | home	74,952
Avalon at Edgewater [Member]
Loss Contingencies [Line Items]
Total number of class action lawsuits	5
Number of operating apartment communities | building	2
Number of operating apartment communities, uninhabitable | building	1
Number of units in operating apartment communities, uninhabitable | home	240
Number of apartment homes included in operating apartment communities owned | home	168
Loss contingency, new class action claims filed number	3
Loss contingency, total class action claims filed number	4
Loss contingency, new claims filed, number	19
Loss contingency, number of plaintiffs | plaintiff	146
Loss contingency, new subrogation claims filed, number	5
Loss contingency, subrogation claims filed dismissed, number	1
Loss contingency, subrogation claims filed pending, number	4

Interest Capitalized (Details)

Interest Capitalized (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Interest Capitalized
Capitalized interest during the development and redevelopment of real estate assets	$ 17,821	$ 20,609

Mortgage Notes Payable, Unsec29

Mortgage Notes Payable, Unsecured Notes and Credit Facility (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Notes Payable, Unsecured Notes and Credit Facility
Total mortgage notes payable and unsecured notes	$ 7,054,852	$ 7,076,758
Credit Facility	0	0
Total mortgage notes payable, unsecured notes and Credit Facility	7,054,852	7,076,758
Unsecured notes
Notes Payable, Unsecured Notes and Credit Facility
Fixed rate notes	4,200,000	4,200,000
Total mortgage notes payable and unsecured notes	4,500,000
Amount of debt discount	8,640	8,930
Amount of deferred financing costs, net	26,814	27,768
Term Loans
Notes Payable, Unsecured Notes and Credit Facility
Variable rate notes	300,000	300,000
Secured notes
Notes Payable, Unsecured Notes and Credit Facility
Fixed rate notes	1,664,650	1,668,496
Variable rate notes	890,202	908,262
Total mortgage notes payable and unsecured notes	2,275,860
Amount of debt discount	3,044
Amount of deferred financing costs, net	$ 10,625	11,046
Amount of debt premium		$ (1,866)

Mortgage Notes Payable, Unsec30

Mortgage Notes Payable, Unsecured Notes and Credit Facility (Details 2) - USD ($)	1 Months Ended	3 Months Ended
	Feb. 28, 2017	Mar. 31, 2017	Dec. 31, 2016
Notes Payable, Unsecured Notes and Credit Facility
Variable rate unsecured credit facility		$ 0	$ 0
Net carrying value of apartment communities and improved land parcels securing debt		3,405,173,000
Mortgage notes payable
Notes Payable, Unsecured Notes and Credit Facility
Mortgage notes payable held by wholly owned subsidiaries guaranteed by the Company		$ 100,000,000
Notes Payable Maturities 2017 [Member] | Mortgage notes payable
Notes Payable, Unsecured Notes and Credit Facility
Repayments of secured mortgages	$ 17,300,000
Variable Rate Unsecured Term Loan $100 Million [Member]
Notes Payable, Unsecured Notes and Credit Facility
Debt instrument, face amount	100,000,000
Variable Rate Unsecured Term Loan $100 Million [Member] | LIBOR
Notes Payable, Unsecured Notes and Credit Facility
Debt instrument variable rate		LIBOR
Debt instrument, basis spread on variable rate (as a percent)		0.90%
Variable Rate Unsecured Term Loan $150 Million [Member]
Notes Payable, Unsecured Notes and Credit Facility
Debt instrument, face amount	$ 150,000,000
Variable Rate Unsecured Term Loan $150 Million [Member] | LIBOR
Notes Payable, Unsecured Notes and Credit Facility
Debt instrument variable rate		LIBOR
Debt instrument, basis spread on variable rate (as a percent)		1.50%
Variable rate unsecured credit facility
Notes Payable, Unsecured Notes and Credit Facility
Available borrowing capacity		$ 1,500,000,000
Line of credit facility, extension period		9 months
Extension fee		$ 1,500,000
Period of borrowing rate assumed		1 month
Annual facility fee, percentage		0.125%
Annual facility fee		$ 1,875,000
Variable rate unsecured credit facility		0	0
Outstanding balance of letters of credit		$ 45,084,000	$ 46,711,000
Variable rate unsecured credit facility | LIBOR
Notes Payable, Unsecured Notes and Credit Facility
Debt instrument variable rate		LIBOR
Debt instrument, basis spread on variable rate (as a percent)		0.825%
Current interest rate (as a percent)		1.81%
Fixed rate mortgage notes payable
Notes Payable, Unsecured Notes and Credit Facility
Weighted average interest rate, debt (as a percent)		4.40%	4.40%
Variable rate mortgage notes payable, unsecured term loan and Credit Facility
Notes Payable, Unsecured Notes and Credit Facility
Weighted average interest rate, debt (as a percent)		2.50%	2.30%

Mortgage Notes Payable, Unsec31

Mortgage Notes Payable, Unsecured Notes and Credit Facility (Details 3) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Dec. 31, 2016
Notes Payable, Unsecured Notes and Credit Facility
Mortgage notes payable and unsecured notes	$ 7,054,852	$ 7,076,758
Variable Rate Unsecured Term Loan $100 Million [Member] | LIBOR
Notes Payable, Unsecured Notes and Credit Facility
Debt instrument variable rate	LIBOR
Debt instrument, basis spread on variable rate (as a percent)	0.90%
Variable Rate Unsecured Term Loan $150 Million [Member] | LIBOR
Notes Payable, Unsecured Notes and Credit Facility
Debt instrument variable rate	LIBOR
Debt instrument, basis spread on variable rate (as a percent)	1.50%
Secured notes
Notes Payable, Unsecured Notes and Credit Facility
Secured notes payments	$ 278,992
Mortgage notes payable and unsecured notes	2,275,860
Secured notes | Notes Payable Maturities 2017 [Member]
Notes Payable, Unsecured Notes and Credit Facility
Secured notes payments	13,954
Mortgage notes payable and unsecured notes	692,191
Secured notes | Notes Payable Maturities 2018 [Member]
Notes Payable, Unsecured Notes and Credit Facility
Secured notes payments	17,789
Mortgage notes payable and unsecured notes	76,667
Secured notes | Notes Payable Maturities 2019 [Member]
Notes Payable, Unsecured Notes and Credit Facility
Secured notes payments	4,696
Mortgage notes payable and unsecured notes	655,514
Secured notes | Notes Payable Maturities 2020 [Member]
Notes Payable, Unsecured Notes and Credit Facility
Secured notes payments	3,624
Mortgage notes payable and unsecured notes	118,729
Secured notes | Notes Payable Maturities 2021 [Member]
Notes Payable, Unsecured Notes and Credit Facility
Secured notes payments	3,551
Mortgage notes payable and unsecured notes	27,844
Secured notes | Notes payable maturing in 2022
Notes Payable, Unsecured Notes and Credit Facility
Secured notes payments	3,795
Secured notes | Notes Payable Maturities 2023 [Member]
Notes Payable, Unsecured Notes and Credit Facility
Secured notes payments	4,040
Secured notes | Notes Payable Maturities 2024 [Member]
Notes Payable, Unsecured Notes and Credit Facility
Secured notes payments	4,310
Secured notes | Notes Payable Maturities 2025 [Member]
Notes Payable, Unsecured Notes and Credit Facility
Secured notes payments	4,585
Mortgage notes payable and unsecured notes	84,835
Secured notes | Notes Payable Maturities 2026 [Member]
Notes Payable, Unsecured Notes and Credit Facility
Secured notes payments	4,894
Secured notes | Notes Payable Maturities Thereafter [Member]
Notes Payable, Unsecured Notes and Credit Facility
Secured notes payments	213,754
Mortgage notes payable and unsecured notes	620,080
Unsecured notes
Notes Payable, Unsecured Notes and Credit Facility
Mortgage notes payable and unsecured notes	4,500,000
Unsecured notes | Notes Payable 6.100 Percent Maturities 2020
Notes Payable, Unsecured Notes and Credit Facility
Mortgage notes payable and unsecured notes	$ 250,000
Stated interest rate of unsecured notes (as a percent)	6.10%
Unsecured notes | Notes Payable 3.625 Percent Maturities 2020
Notes Payable, Unsecured Notes and Credit Facility
Mortgage notes payable and unsecured notes	$ 400,000
Stated interest rate of unsecured notes (as a percent)	3.625%
Unsecured notes | Notes Payable Maturities 2021 [Member]
Notes Payable, Unsecured Notes and Credit Facility
Mortgage notes payable and unsecured notes	$ 250,000
Stated interest rate of unsecured notes (as a percent)	3.95%
Unsecured notes | Variable Rate Unsecured Term Loan $300 Million [Member]
Notes Payable, Unsecured Notes and Credit Facility
Mortgage notes payable and unsecured notes	$ 300,000
Unsecured notes | Variable Rate Unsecured Term Loan $300 Million [Member] | LIBOR
Notes Payable, Unsecured Notes and Credit Facility
Debt instrument variable rate	LIBOR
Debt instrument, basis spread on variable rate (as a percent)	1.45%
Unsecured notes | Notes payable maturing in 2022
Notes Payable, Unsecured Notes and Credit Facility
Mortgage notes payable and unsecured notes	$ 450,000
Stated interest rate of unsecured notes (as a percent)	2.95%
Unsecured notes | Notes payable maturing in 2023
Notes Payable, Unsecured Notes and Credit Facility
Mortgage notes payable and unsecured notes	$ 350,000
Stated interest rate of unsecured notes (as a percent)	4.20%
Unsecured notes | Notes Payable 2.850 Maturities 2023
Notes Payable, Unsecured Notes and Credit Facility
Mortgage notes payable and unsecured notes	$ 250,000
Stated interest rate of unsecured notes (as a percent)	2.85%
Unsecured notes | Notes Payable Maturities 2024 [Member]
Notes Payable, Unsecured Notes and Credit Facility
Mortgage notes payable and unsecured notes	$ 300,000
Stated interest rate of unsecured notes (as a percent)	3.50%
Unsecured notes | Notes Payable 3.450 Maturities 2025 [Member]
Notes Payable, Unsecured Notes and Credit Facility
Mortgage notes payable and unsecured notes	$ 525,000
Stated interest rate of unsecured notes (as a percent)	3.45%
Unsecured notes | Notes Payable 3.500 Maturities 2025 [Member]
Notes Payable, Unsecured Notes and Credit Facility
Mortgage notes payable and unsecured notes	$ 300,000
Stated interest rate of unsecured notes (as a percent)	3.50%
Unsecured notes | Notes Payable 2.950 Maturities 2026 [Member]
Notes Payable, Unsecured Notes and Credit Facility
Mortgage notes payable and unsecured notes	$ 475,000
Stated interest rate of unsecured notes (as a percent)	2.95%
Unsecured notes | Notes Payable 2.900 Maturities 2026 [Member]
Notes Payable, Unsecured Notes and Credit Facility
Mortgage notes payable and unsecured notes	$ 300,000
Stated interest rate of unsecured notes (as a percent)	2.90%
Unsecured notes | Notes Payable Maturities 2046 [Member]
Notes Payable, Unsecured Notes and Credit Facility
Mortgage notes payable and unsecured notes	$ 350,000
Stated interest rate of unsecured notes (as a percent)	3.90%

Equity (Details)

Equity (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Changes in equity
Beginning Balance	$ 10,171,416
Net income attributable to common stockholders	235,875	$ 237,931
(Loss) income on cash flow hedges	145	(47,757)
Cash flow hedge loss reclassified to earnings	1,752	1,374
Change in redemption value of redeemable noncontrolling interest	(183)
Dividends declared to common stockholders	(195,657)
Issuance of common stock, net of withholdings	46,707
Amortization of deferred compensation	6,567
Ending Balance	10,266,622
Common stock
Changes in equity
Beginning Balance	1,373
Issuance of common stock, net of withholdings	5
Ending Balance	1,378
Additional paid-in capital
Changes in equity
Beginning Balance	10,105,654
Issuance of common stock, net of withholdings	47,962
Amortization of deferred compensation	6,567
Ending Balance	10,160,183
Accumulated earnings less dividends
Changes in equity
Beginning Balance	94,899
Net income attributable to common stockholders	235,875
Change in redemption value of redeemable noncontrolling interest	(183)	$ 299
Dividends declared to common stockholders	(195,657)
Issuance of common stock, net of withholdings	(1,260)
Ending Balance	133,674
Accumulated other comprehensive loss
Changes in equity
Beginning Balance	(30,510)
(Loss) income on cash flow hedges	145
Cash flow hedge loss reclassified to earnings	1,752
Ending Balance	$ (28,613)

Equity (Details 2)

Equity (Details 2) - USD ($)	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Class of Stock [Line Items]
Common stock, shares authorized (in shares)	280,000,000		280,000,000
Preferred stock, shares authorized (in shares)	50,000,000		50,000,000
Common stock shares issued in connection with stock options exercised (in shares)	7,266
Common stock issued through the dividend reinvestment plan (in shares)	1,165	576
Number of shares of stock grants withheld (in shares)	57,172	48,189
Stock Issued During Period, Shares, Share-based Compensation, Forfeited (in shares)	236
Issuance of common stock, net	$ 56,817,000	$ 1,102,000
Continuous Equity Program CEP IV [Member]
Class of Stock [Line Items]
Common stock shares issued	306,177
Maximum value of shares of common stock that can be sold (in dollars)	$ 1,000,000,000
Shares issued, price per share (in dollars per share)	$ 186.44
Issuance of common stock, net	$ 56,228,000
Common stock value, remaining to be authorized under continuous equity program	$ 942,915,000
Maximum [Member] | Continuous Equity Program CEP IV [Member]
Class of Stock [Line Items]
Percentage of compensation received by sales agent	2.00%
Restricted Stock and Restricted Stock Converted From Performance Shares [Member]
Class of Stock [Line Items]
Restricted stock granted (in shares)	198,502	193,171

Investments in Real Estate En34

Investments in Real Estate Entities (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2017USD ($)entityhome	Mar. 31, 2016USD ($)	Dec. 31, 2016USD ($)
Investment in Real Estate Entities
Gain on sale of communities	$ 29,447	$ 103,321
Equity method investment, difference between carrying amount and underlying equity	37,148		$ 38,015
Other than temporary impairment losses, investments	$ 0	$ 0
Unconsolidated real estate entities
Investment in Real Estate Entities
Number of unconsolidated real estate entities | entity	5
Unconsolidated real estate entities | Minimum
Investment in Real Estate Entities
Equity method investment, ownership percentage	20.00%
Unconsolidated real estate entities | Maximum
Investment in Real Estate Entities
Equity method investment, ownership percentage	31.30%
Avalon Bay Value Added Fund II LP [Member]
Investment in Real Estate Entities
Equity method investment, ownership percentage	31.30%
Percentage of right of distribution	20.00%
Percentage of right of remaining distribution	80.00%
Proceeds from equity method investment, dividends or distributions	$ 6,765
Avalon Bay Value Added Fund II LP [Member] | Eaves Gaithersburg [Member]
Investment in Real Estate Entities
Number of apartment homes sold | home	684
Proceeds from sale of real estate	$ 117,000
Gain on sale of communities	8,697
Repayments of secured mortgages	$ 63,200

Investments in Real Estate En35

Investments in Real Estate Entities (Details 2) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Assets:
Real estate, net	$ 862,612		$ 954,493
Other assets	76,208		49,519
Total assets	938,820		1,004,012
Liabilities and partners' capital:
Mortgage notes payable and credit facility	625,256		689,573
Other liabilities	15,861		16,537
Partners' capital	297,703		297,902
Total liabilities and partners' capital	938,820		$ 1,004,012
Combined summary of the operating results of the accounted for using the equity method
Rental and other income	28,642	$ 36,955
Operating and other expenses	(11,094)	(14,170)
Gain on sale of communities	29,447	103,321
Interest expense, net	(6,948)	(20,001)
Depreciation expense	(7,327)	(9,240)
Net income	$ 32,720	96,865
Funds [Member]
Combined summary of the operating results of the accounted for using the equity method
Gains (losses) on extinguishment of debt		$ 10,864

Investments in Real Estate En36

Investments in Real Estate Entities (Details 3) $ in Thousands	3 Months Ended		15 Months Ended
	Mar. 31, 2017USD ($)	Mar. 31, 2016USD ($)land_parcel	Mar. 31, 2016USD ($)	Dec. 31, 2016USD ($)
Business Acquisition [Line Items]
Business Combination, Acquisition Related Costs, Abandoned Pursuit Costs	$ 728	$ 746
Real Estate [Line Items]
Casualty and impairment loss (gain), net	(11,688)	$ 2,202
Number of land parcels impaired | land_parcel		2
Net operating real estate	15,171,803			$ 15,045,593
Insurance proceeds for property damage claims	4,095	$ 8,702
Insurance proceeds receivable	287,130			$ 256,934
Land [Member]
Real Estate [Line Items]
Casualty and impairment loss (gain), net	(9,350)	(6,500)
Avalon Maplewood [Member]
Real Estate [Line Items]
Casualty and impairment loss (gain), net	(2,338)
Casualty loss	19,481
Net operating real estate	16,361
Other nonrecurring expense	3,120
Insurance Recoveries	17,143
Insurance proceeds for property damage claims	4,545
Insurance proceeds receivable	$ 12,598
Avalon at Edgewater [Member]
Real Estate [Line Items]
Casualty and impairment loss (gain), net		8,702
Insurance Recoveries		29,008	$ 73,150
Gain on business interruption insurance recovery		$ 20,306
Avalon Brooklyn Bay [Member]
Business Acquisition [Line Items]
Variable Interest Entity, Qualitative or Quantitative Information, Ownership Percentage	70.00%
Variable Interest Entity, Ownership Interest by Partner	30.00%
Due from Related Parties	$ 32,036

Real Estate Disposition Activ37

Real Estate Disposition Activities (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2017USD ($)communityland_parcelhome	Mar. 31, 2016USD ($)
Summary of income from discontinued operations
Gain on sale of communities	$ 87,949	$ 51,430
Number of land parcels sold | land_parcel	2
Number of owned communities under construction | community	24
Gain on sale of other real estate	$ 366	$ 0
Number of communities held for sale | community	0
Avalon Pines [Member]
Summary of income from discontinued operations
Apartment homes | home	450
Proceeds from sale of real estate	$ 140,000
Gain on sale of communities	87,949
Other Real Estate Sales [Member]
Summary of income from discontinued operations
Proceeds from sale of real estate	22,286
Gain on sale of other real estate	$ 366
Development Communities [Member] | Avalon Newcastle Commons I [Member]
Summary of income from discontinued operations
Number of owned communities under construction | community	1

Segment Reporting (Details)

Segment Reporting (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Reconciliation of NOI to net income
Net income	$ 235,781	$ 237,877
Indirect operating expenses, net of corporate income	16,297	16,537
Investments and investment management expense	1,321	1,145
Expensed acquisition, development and other pursuit costs, net of recoveries	728	3,462
Interest expense, net	49,295	43,410
General and administrative expense	13,206	11,404
Equity in income of unconsolidated real estate entities	(16,672)	(27,969)
Depreciation expense	140,621	127,216
Income tax expense	20	37
Casualty and impairment loss (gain), net	11,688	(2,202)
Gain on sale of real estate	(88,315)	(51,430)
Net operating income from real estate assets sold or held for sale	(1,387)	(8,606)
Net operating income	$ 362,583	$ 350,881

Segment Reporting (Details 2)

Segment Reporting (Details 2) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Segment Reporting [Abstract]
Rental income from real estate assets sold or held for sale	$ 2,650	$ 13,916
Operating expenses from real estate assets sold or held for sale	(1,263)	(5,310)
Net operating income from real estate assets sold or held for sale	$ 1,387	$ 8,606

Segment Reporting (Details 3)

Segment Reporting (Details 3) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Segment Reporting
Total revenue	$ 522,326	$ 508,498
NOI	$ 362,583	$ 350,881
% NOI change from prior year	3.30%	21.70%
Gross real estate	$ 20,919,484	$ 19,721,229
Gross real estate assets held for sale		20,341
Avalon at Edgewater [Member]
Segment Reporting
Gain on business interruption insurance recovery		20,306
Operating Segments | Established
Segment Reporting
Total revenue	388,908	366,803
NOI	$ 276,106	$ 258,640
% NOI change from prior year	3.90%	7.90%
Gross real estate	$ 13,393,588	$ 13,155,449
Operating Segments | Established | New England [Member]
Segment Reporting
Total revenue	58,607	57,196
NOI	$ 37,816	$ 36,508
% NOI change from prior year	3.30%	15.90%
Gross real estate	$ 1,875,024	$ 1,860,863
Operating Segments | Established | Metro NY/NJ
Segment Reporting
Total revenue	87,544	83,079
NOI	$ 60,060	$ 56,702
% NOI change from prior year	3.80%	3.20%
Gross real estate	$ 2,903,317	$ 2,883,958
Operating Segments | Established | Mid-Atlantic
Segment Reporting
Total revenue	55,755	57,530
NOI	$ 39,147	$ 40,063
% NOI change from prior year	3.70%	1.30%
Gross real estate	$ 2,062,311	$ 2,330,106
Operating Segments | Established | Pacific Northwest
Segment Reporting
Total revenue	20,454	19,289
NOI	$ 14,815	$ 14,078
% NOI change from prior year	5.20%	5.80%
Gross real estate	$ 731,537	$ 795,228
Operating Segments | Established | Northern California
Segment Reporting
Total revenue	83,323	78,452
NOI	$ 63,717	$ 60,248
% NOI change from prior year	2.00%	11.50%
Gross real estate	$ 2,815,589	$ 2,651,741
Operating Segments | Established | Southern California
Segment Reporting
Total revenue	83,225	71,257
NOI	$ 60,551	$ 51,041
% NOI change from prior year	6.20%	9.80%
Gross real estate	$ 3,005,810	$ 2,633,553
Operating Segments | Other Stabilized
Segment Reporting
Total revenue	74,021	73,004
NOI	51,571	56,914
Gross real estate	3,032,689	2,196,700
Operating Segments | Development / Redevelopment
Segment Reporting
Total revenue	55,547	53,251
NOI	34,906	35,327
Gross real estate	4,276,266	3,802,952
Land Held for Future Development
Segment Reporting
Gross real estate	103,954	477,072
Non-allocated
Segment Reporting
Total revenue	1,200	1,524
Gross real estate	112,987	89,056
Continuing Operations
Segment Reporting
Total revenue	$ 519,676	$ 494,582

Stock-Based Compensation Plan41

Stock-Based Compensation Plans (Details)	3 Months Ended
	Mar. 31, 2017$ / sharesshares
Shares
Exercised (in shares)	(7,266)
2009 Plan | Employee and Directors Stock Options [Member]
Shares
Options outstanding at the beginning of the period (in shares)	177,333
Exercised (in shares)	(3,085)
Forfeited (in shares)	0
Options outstanding at the end of the period (in shares)	174,248
Weighted average exercise price per share
Options outstanding at the beginning of the period (in dollars per share) | $ / shares	$ 124.25
Exercised (in dollars per share) | $ / shares	120.74
Forfeited (in dollars per share) | $ / shares	0
Options outstanding at the end of the period (in dollars per share) | $ / shares	$ 124.31
1994 Plan | Employee and Directors Stock Options [Member]
Shares
Options outstanding at the beginning of the period (in shares)	22,541
Exercised (in shares)	(4,181)
Forfeited (in shares)	0
Options outstanding at the end of the period (in shares)	18,360
Weighted average exercise price per share
Options outstanding at the beginning of the period (in dollars per share) | $ / shares	$ 77.91
Exercised (in dollars per share) | $ / shares	129.72
Forfeited (in dollars per share) | $ / shares	0
Options outstanding at the end of the period (in dollars per share) | $ / shares	$ 66.11

Stock-Based Compensation Plan42

Stock-Based Compensation Plans (Details 2) - Performance Shares	3 Months Ended
	Mar. 31, 2017$ / sharesshares
Performance awards
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number (in shares)	251,163
Restricted stock granted (in shares)	81,708
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Increase (Decrease) in Awards Based on Performance (in shares)	49,323
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Converted to Restricted Stock (in shares)	(128,482)
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period (in shares)	(792)
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number (in shares)	252,920
Weighted average grant date fair value per award
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value (in dollars per share) | $ / shares	$ 136.74
Grant date fair value per share (in dollars per share) | $ / shares	176.59
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Change in Awards Based on Performance, Weighted Average Grant Date Fair Value (in dollars per share) | $ / shares	119.26
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Converted to Restricted Stock, Weighted Average Grant Date Fair Value (in dollars per share) | $ / shares	118.75
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeitures, Weighted Average Grant Date Fair Value (in dollars per share) | $ / shares	160.39
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value (in dollars per share) | $ / shares	$ 155.27
Share-based Compensation Arrangement By Share-Based Payment Award, Equity Instruments Other Than Options, Grants In Period Based On Total Shareholder Metrics (in shares)	49,374
Share-based Compensation Arrangement By Share-Based Payment Award, Equity Instruments Other Than Options, Grants In Period Based On Financial Metrics (in shares)	32,334

Stock-Based Compensation Plan43

Stock-Based Compensation Plans Stock-Based Compensation Plans (Details 3) - Performance Shares	3 Months Ended
	Mar. 31, 2017$ / shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Dividend yield (as a percent)	3.20%
Estimated volatility, Minimum (as a percent)	15.30%
Estimated volatility, Maximum (as a percent)	19.70%
Risk-free interest rate, minimum (as a percent)	0.69%
Risk-free interest rate, maximum (as a percent)	1.61%
Average estimated fair value (in dollars per share)	$ 175.86
Historical volatility (as a percent)	50.00%
Implied volatility (as a percent)	50.00%

Stock-Based Compensation Plan44

Stock-Based Compensation Plans Stock-Based Compensation Plans (Details 4) - $ / shares	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Restricted Stock [Member]
Restricted stock shares
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number (in shares)	136,705
Restricted stock granted (in shares)	70,020	77,553
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period (in shares)	(65,702)
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period (in shares)	(236)
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number (in shares)	140,787
Restricted stock shares weighted average grant date fair value per share
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value (in dollars per share)	$ 158.51
Grant date fair value per share (in dollars per share)	179.07
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Weighted Average Grant Date Fair Value (in dollars per share)	153.05
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeitures, Weighted Average Grant Date Fair Value (in dollars per share)	173.73
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value (in dollars per share)	$ 171.25
Restricted Stock Converted From Performance Shares [Member]
Restricted stock shares
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number (in shares)	176,698
Restricted stock granted (in shares)	128,482	115,618
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period (in shares)	(69,149)
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period (in shares)	0
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number (in shares)	236,031

Stock-Based Compensation Plan45

Stock-Based Compensation Plans (Details 5) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Additional disclosures
Stock-based compensation expense	$ 3,986	$ 3,742
Capitalized stock-based compensation cost	$ 2,078	$ 3,048
Performance Shares
Additional disclosures
Grant date value (in dollars per share)	$ 179.07
Restricted stock and restricted stock units
Additional disclosures
Unrecognized compensation cost for unvested restricted stock	$ 45,637
Weighted average period for recognition of unrecognized compensation cost	3 years 10 months 24 days

Related Party Arrangements (Det

Related Party Arrangements (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Related Party Arrangements
Management Fees Revenue	$ 1,200	$ 1,524
Compensation expense	3,986	3,742
Unconsolidated real estate entities
Related Party Arrangements
Outstanding receivables	3,846		$ 5,239
Non Employee Director [Member] | Restricted stock and deferred stock awards
Related Party Arrangements
Compensation expense	371	$ 341
Amount of deferred compensation	$ 212		$ 531

Fair Value (Details)

Fair Value (Details)	3 Months Ended
	Mar. 31, 2017USD ($)derivativeventure	Mar. 31, 2016USD ($)
Derivative instruments and Hedging Activities
(Loss) income on cash flow hedges	$ 145,000	$ (47,757,000)
Estimated hedging losses to be reclassified from accumulated other comprehensive loss into earnings within the next twelve months	$ 6,975,000
Cash Flow Hedges
Derivative instruments and Hedging Activities
Number of derivative instruments held | derivative	13
Interest Rate Cap [Member] | Cash Flow Hedges
Derivative instruments and Hedging Activities
Notional amount	$ 35,685,000
Weighted average interest rate (as a percent)	2.80%
Weighted average capped interest rate (as a percent)	5.90%
Interest Rate Swap [Member] | Cash Flow Hedges
Derivative instruments and Hedging Activities
Notional amount	$ 900,000,000
Weighted average capped interest rate (as a percent)	2.30%
Notional amounts entered into during period	$ 100,000,000
Put Option [Member]
Derivative instruments and Hedging Activities
Number of Ventures in which Entity is Required to Purchase Interest in Investment at Guaranteed Minimum Amount | venture	3
Not Designated as Hedging Instrument [Member]
Derivative instruments and Hedging Activities
Number of derivative instruments held | derivative	14
Not Designated as Hedging Instrument [Member] | Interest Rate Cap [Member]
Derivative instruments and Hedging Activities
Notional amount	$ 696,591,000
Weighted average interest rate (as a percent)	2.60%
Weighted average capped interest rate (as a percent)	6.10%

Fair Value (Details 2)

Fair Value (Details 2) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Fair Value Disclosures [Abstract]
Cash flow hedge losses reclassified to earnings	$ (1,752)	$ (1,374)

Fair Value (Details 3)

Fair Value (Details 3) - Recurring basis - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Estimate of Fair Value Measurement [Member]
Financial Instruments Measured/Discussed at Fair Value
DownREIT units	$ (1,377)	$ (1,329)
Total	(6,962,494)	(6,955,564)
Estimate of Fair Value Measurement [Member] | Unsecured notes
Financial Instruments Measured/Discussed at Fair Value
Indebtedness	(4,226,278)	(4,218,627)
Estimate of Fair Value Measurement [Member] | Secured Debt and Variable Rate Unsecured Term Loan [Member]
Financial Instruments Measured/Discussed at Fair Value
Indebtedness	(2,743,794)	(2,744,462)
Estimate of Fair Value Measurement [Member] | Interest Rate Cap [Member] | Cash Flow Hedges
Financial Instruments Measured/Discussed at Fair Value
Derivative assets		2
Estimate of Fair Value Measurement [Member] | Interest Rate Cap [Member] | Not Designated as Hedging Instrument [Member]
Financial Instruments Measured/Discussed at Fair Value
Derivative assets	30	79
Estimate of Fair Value Measurement [Member] | Interest Rate Swap [Member] | Cash Flow Hedges
Financial Instruments Measured/Discussed at Fair Value
Derivative assets	14,955	14,775
Derivative Liability	(102)
Estimate of Fair Value Measurement [Member] | Put Option [Member]
Financial Instruments Measured/Discussed at Fair Value
Fair value of remaining outstanding Puts	(5,928)	(6,002)
Fair Value, Inputs, Level 1 [Member]
Financial Instruments Measured/Discussed at Fair Value
DownREIT units	(1,377)	(1,329)
Total	(4,227,655)	(4,219,956)
Fair Value, Inputs, Level 1 [Member] | Unsecured notes
Financial Instruments Measured/Discussed at Fair Value
Indebtedness	(4,226,278)	(4,218,627)
Fair Value, Inputs, Level 2 [Member]
Financial Instruments Measured/Discussed at Fair Value
Total	(2,728,911)	(2,729,606)
Fair Value, Inputs, Level 2 [Member] | Secured Debt and Variable Rate Unsecured Term Loan [Member]
Financial Instruments Measured/Discussed at Fair Value
Indebtedness	(2,743,794)	(2,744,462)
Fair Value, Inputs, Level 2 [Member] | Interest Rate Cap [Member] | Cash Flow Hedges
Financial Instruments Measured/Discussed at Fair Value
Derivative assets		2
Fair Value, Inputs, Level 2 [Member] | Interest Rate Cap [Member] | Not Designated as Hedging Instrument [Member]
Financial Instruments Measured/Discussed at Fair Value
Derivative assets	30	79
Fair Value, Inputs, Level 2 [Member] | Interest Rate Swap [Member] | Cash Flow Hedges
Financial Instruments Measured/Discussed at Fair Value
Derivative assets	14,955	14,775
Derivative Liability	(102)
Fair Value, Inputs, Level 3 [Member]
Financial Instruments Measured/Discussed at Fair Value
Total	(5,928)	(6,002)
Fair Value, Inputs, Level 3 [Member] | Put Option [Member]
Financial Instruments Measured/Discussed at Fair Value
Fair value of remaining outstanding Puts	$ (5,928)	$ (6,002)

Subsequent Events (Details)

Subsequent Events (Details)	May 02, 2017USD ($)community	Feb. 28, 2017USD ($)	Apr. 30, 2017USD ($)	Mar. 31, 2017USD ($)community	Dec. 31, 2016USD ($)
Subsequent Event [Line Items]
Number of operating apartment communities | community				260
Variable rate unsecured credit facility				$ 0	$ 0
Variable Rate Unsecured Term Loan $250 Million [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Debt instrument, face amount			$ 250,000,000
Variable Rate Unsecured Term Loan $100 Million [Member]
Subsequent Event [Line Items]
Debt instrument, face amount		$ 100,000,000
Variable Rate Unsecured Term Loan $150 Million [Member]
Subsequent Event [Line Items]
Debt instrument, face amount		150,000,000
Variable rate unsecured credit facility
Subsequent Event [Line Items]
Variable rate unsecured credit facility				$ 0	$ 0
Variable rate unsecured credit facility | Subsequent Event [Member]
Subsequent Event [Line Items]
Variable rate unsecured credit facility	$ 395,000,000
Secured notes | Subsequent Event [Member]
Subsequent Event [Line Items]
Repayments of secured mortgages	$ 498,357,000
Number of operating apartment communities | community	8
Secured notes | Notes Payable Maturities 2017 [Member]
Subsequent Event [Line Items]
Repayments of secured mortgages		$ 17,300,000
Secured notes | Notes Payable Maturities 2017 [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Debt instrument, interest rate, effective percentage	3.36%