Extra Space Storage (EXR) 10-Q 8 May 15 2015 Q1 Quarterly report Financial data

Document_and_Entity_Informatio

Document and Entity Information	3 Months Ended
	Mar. 31, 2015	Apr. 30, 2015
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	FALSE
Document Period End Date	31-Mar-15
Document Fiscal Year Focus	2015
Document Fiscal Period Focus	Q1
Trading Symbol	EXR
Entity Registrant Name	Extra Space Storage Inc.
Entity Central Index Key	1289490
Current Fiscal Year End Date	-19
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		116,494,142

Condensed_Consolidated_Balance

Condensed Consolidated Balance Sheets (USD $)	Mar. 31, 2015	Dec. 31, 2014
In Thousands, unless otherwise specified
Assets:
Real estate assets, net	$4,197,853	$4,135,696
Investments in unconsolidated real estate ventures	85,602	85,711
Cash and cash equivalents	45,304	47,663
Restricted cash	35,350	25,245
Receivables from related parties and affiliated real estate joint ventures	3,136	11,778
Other assets, net	96,900	96,014
Total assets	4,464,145	4,402,107
Liabilities, Noncontrolling Interests and Equity:
Notes payable	1,972,957	1,872,067
Premium on notes payable	2,534	3,281
Exchangeable senior notes	250,000	250,000
Discount on exchangeable senior notes	-12,169	-13,054
Notes payable to Trusts	119,590	119,590
Lines of credit	99,000	138,000
Accounts payable and accrued expenses	71,553	65,521
Other liabilities	53,625	54,719
Total liabilities	2,557,090	2,490,124
Commitments and contingencies
Extra Space Storage Inc. stockholders' equity:
Preferred stock, $0.01 par value, 50,000,000 shares authorized, no shares issued or outstanding
Common stock, $0.01 par value, 500,000,000 shares authorized, 116,458,159 and 116,360,239 shares issued and outstanding at March 31, 2015 and December 31, 2014, respectively	1,164	1,163
Additional paid-in capital	1,998,240	1,995,484
Accumulated other comprehensive loss	-7,800	-1,484
Accumulated deficit	-258,728	-257,738
Total Extra Space Storage Inc. stockholders' equity	1,732,876	1,737,425
Noncontrolling interest represented by Preferred Operating Partnership units, net of $120,230 notes receivable	81,088	81,152
Noncontrolling interests in Operating Partnership	92,105	92,422
Other noncontrolling interests	986	984
Total noncontrolling interests and equity	1,907,055	1,911,983
Total liabilities, noncontrolling interests and equity	$4,464,145	$4,402,107

Condensed_Consolidated_Balance1

Condensed Consolidated Balance Sheets (Parenthetical) (USD $)	Mar. 31, 2015	Dec. 31, 2014
In Thousands, except Share data, unless otherwise specified
Statement of Financial Position [Abstract]
Preferred stock, par value	$0.01	$0.01
Preferred stock, shares authorized	50,000,000	50,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$0.01	$0.01
Common stock, shares authorized	500,000,000	500,000,000
Common stock, shares issued	116,458,159	116,360,239
Common stock, shares outstanding	116,458,159	116,360,239
Note receivable from noncontrolling interest represented by Preferred Operating Partnership units	$120,230	$120,230

Condensed_Consolidated_Stateme

Condensed Consolidated Statements of Operations (USD $)	3 Months Ended
In Thousands, except Share data, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Revenues:
Property rental	$148,894	$132,001
Tenant reinsurance	16,510	13,463
Management fees and other income	7,750	7,123
Total revenues	173,154	152,587
Expenses:
Property operations	47,244	43,482
Tenant reinsurance	2,928	2,567
Acquisition related costs	869	2,056
General and administrative	16,249	15,709
Depreciation and amortization	30,428	28,375
Total expenses	97,718	92,189
Income from operations	75,436	60,398
Interest expense	-21,431	-19,598
Non-cash interest expense related to amortization of discount on equity component of exchangeable senior notes	-697	-662
Interest income	856	269
Interest income on note receivable from Preferred Operating Partnership unit holder	1,213	1,213
Income before equity in earnings of unconsolidated real estate ventures and income tax expense	55,377	41,620
Equity in earnings of unconsolidated real estate ventures	2,650	2,419
Equity in earnings of unconsolidated real estate ventures-gain on sale of real estate assets and purchase of joint venture partners' interests	2,857
Income tax expense	-2,248	-2,830
Net income	58,636	41,209
Net income allocated to Preferred Operating Partnership noncontrolling interests	-2,926	-2,492
Net income allocated to Operating Partnership and other noncontrolling interests	-1,968	-1,377
Net income attributable to common stockholders	$53,742	$37,340
Earnings per common share
Basic	$0.46	$0.32
Diluted	$0.46	$0.32
Weighted average number of shares
Basic	116,117,615	115,438,325
Diluted	122,595,718	121,062,845
Cash dividends paid per common share	$0.47	$0.40

Condensed_Consolidated_Stateme1

Condensed Consolidated Statements of Comprehensive Income (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Statement of Comprehensive Income [Abstract]
Net income	$58,636	$41,209
Other comprehensive loss:
Change in fair value of interest rate swaps	-6,593	-2,747
Total comprehensive income	52,043	38,462
Less: comprehensive income attributable to noncontrolling interests	4,617	3,750
Comprehensive income attributable to common stockholders	$47,426	$34,712

Condensed_Consolidated_Stateme2

Condensed Consolidated Statement of Noncontrolling Interests and Equity (USD $)	Total	Series A Preferred Operating Partnership [Member]	Series B Preferred Operating Partnership [Member]	Series C Preferred Operating Partnership [Member]	Series D Preferred Operating Partnership [Member]	Common Operating Partnership [Member]	Other [Member]	Par Value [Member]	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive Income [Member]	Accumulated Deficit [Member]
In Thousands, except Share data
Balances at Dec. 31, 2014	$1,911,983	$14,809	$41,903	$10,730	$13,710	$92,422	$984	$1,163	$1,995,484	($1,484)	($257,738)
Balances (in shares) at Dec. 31, 2014	116,360,239							116,360,239
Issuance of common stock upon the exercise of options	970								970
Issuance of common stock upon the exercise of options (in shares)								41,634
Restricted stock grants issued	1							1
Restricted stock grants issued (in shares)								58,150
Restricted stock grants cancelled (in shares)								-1,864
Compensation expense related to stock-based awards	1,142								1,142
Net income	58,636	1,668	629	458	171	1,966	2				53,742
Other comprehensive income	-6,593	-46				-231				-6,316
Tax effect from vesting of restricted stock grants and stock option exercises	644								644
Distributions to Operating Partnership units held by noncontrolling interests	-4,996	-1,686	-629	-458	-171	-2,052
Dividends paid on common stock at $0.47 per share	-54,732										-54,732
Balances at Mar. 31, 2015	$1,907,055	$14,745	$41,903	$10,730	$13,710	$92,105	$986	$1,164	$1,998,240	($7,800)	($258,728)
Balances (in shares) at Mar. 31, 2015	116,458,159							116,458,159

Condensed_Consolidated_Stateme3

Condensed Consolidated Statement of Noncontrolling Interests and Equity (Parenthetical) (USD $)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Statement of Stockholders' Equity [Abstract]
Dividends paid on common stock, per share	$0.47	$0.40

Condensed_Consolidated_Stateme4

Condensed Consolidated Statements of Cash Flows (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Cash flows from operating activities:
Net income	$58,636	$41,209
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	30,428	28,375
Amortization of deferred financing costs	1,598	1,641
Non-cash interest expense related to amortization of discount on equity component of exchangeable senior notes	697	662
Non-cash interest expense related to amortization of premium on notes payable	-747	-895
Compensation expense related to stock-based awards	1,142	1,121
Gain on sale of real estate assets and purchase of joint venture partners' interests	-2,857
Distributions from unconsolidated real estate ventures in excess of earnings	2,601	1,024
Changes in operating assets and liabilities:
Receivables from related parties and affiliated real estate joint ventures	-2,367	-1,424
Other assets	-2,637	1,448
Accounts payable and accrued expenses	6,032	-7,715
Other liabilities	-5,087	-874
Net cash provided by operating activities	87,439	64,572
Cash flows from investing activities:
Acquisition of real estate assets	-77,082	-253,939
Development and redevelopment of real estate assets	-3,140	-2,820
Change in restricted cash	-10,105	1,425
Purchase of equipment and fixtures	-1,184	-1,274
Net cash used in investing activities	-91,511	-256,608
Cash flows from financing activities:
Proceeds from notes payable and lines of credit	290,768	291,157
Principal payments on notes payable and lines of credit	-228,878	-127,881
Deferred financing costs	-1,419	-1,392
Net proceeds from exercise of stock options	970	1,056
Dividends paid on common stock	-54,732	-46,347
Distributions to noncontrolling interests	-4,996	-4,265
Net cash provided by financing activities	1,713	112,328
Net decrease in cash and cash equivalents	-2,359	-79,708
Cash and cash equivalents, beginning of the period	47,663	126,723
Cash and cash equivalents, end of the period	45,304	47,015
Supplemental schedule of cash flow information
Interest paid	21,754	16,445
Income taxes paid	661	1,244
Tax effect from vesting of restricted stock grants and option exercises
Other assets	644	1,262
Paid-in capital	-644	-1,262
Acquisitions of real estate assets
Real estate assets, net	11,009
Receivables from related parties and affiliated real estate joint ventures	($11,009)

Organization

Organization	3 Months Ended
	Mar. 31, 2015
Accounting Policies [Abstract]
Organization	1. ORGANIZATION
	Extra Space Storage Inc. (the “Company”) is a fully-integrated, self-administered and self-managed real estate investment trust (“REIT”), formed as a Maryland corporation on April 30, 2004, to own, operate, manage, acquire, develop and redevelop professionally managed self-storage properties (“stores”) located throughout the United States. The Company continues the business of Extra Space Storage LLC and its subsidiaries, which had engaged in the self-storage business since 1977. The Company’s interests in its stores is held through its operating partnership, Extra Space Storage LP (the “Operating Partnership”), which was formed on May 5, 2004. The Company’s primary assets are general partner and limited partner interests in the Operating Partnership. This structure is commonly referred to as an umbrella partnership REIT (“UPREIT”). The Company has elected to be taxed as a REIT under the Internal Revenue Code of 1986, as amended. To the extent the Company continues to qualify as a REIT, it will not be subject to tax, with certain limited exceptions, on the taxable income that is distributed to its stockholders.
	The Company invests in stores by acquiring wholly-owned stores or by acquiring an equity interest in real estate entities. At March 31, 2015, the Company had direct and indirect equity interests in 835 stores. In addition, the Company managed 271 stores for third parties, bringing the total number of stores which it owns and/or manages to 1,106. These stores are located in 35 states, Washington, D.C. and Puerto Rico.
	The Company operates in three distinct segments: (1) rental operations; (2) tenant reinsurance; and (3) property management, acquisition and development. The rental operations activities include rental operations of stores in which we have an ownership interest. No single tenant accounts for more than 5.0% of rental income. Tenant reinsurance activities include the reinsurance of risks relating to the loss of goods stored by tenants in the Company’s stores. The Company’s property management, acquisition and development activities include managing, acquiring, developing and selling stores.

Basis_of_Presentation

Basis of Presentation	3 Months Ended
	Mar. 31, 2015
Accounting Policies [Abstract]
Basis of Presentation	2. BASIS OF PRESENTATION
	The accompanying unaudited condensed consolidated financial statements of the Company are presented on the accrual basis of accounting in accordance with U.S. generally accepted accounting principles (“GAAP”) for interim financial information, and in accordance with the instructions to Form 10-Q and Article 10 of Regulation S-X. Accordingly, they may not include all of the information and footnotes required by GAAP for complete financial statements. In the opinion of management, all adjustments (including normal recurring accruals) considered necessary for a fair presentation have been included. Operating results for the three months ended March 31, 2015, are not necessarily indicative of results that may be expected for the year ending December 31, 2015. The condensed consolidated balance sheet as of December 31, 2014 has been derived from the Company’s audited financial statements as of that date, but does not include all of the information and footnotes required by GAAP for complete financial statements. For further information refer to the consolidated financial statements and footnotes thereto included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2014, as filed with the Securities and Exchange Commission.
	Reclassifications
	Certain amounts in the Company’s 2014 consolidated financial statements and supporting note disclosures have been reclassified to conform to the current period presentation. Such reclassifications did not impact previously reported net income or accumulated deficit.
	Recently Issued Accounting Standards
	In April 2014, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) 2014-08, “Presentation of Financial Statements (Topic 205) and Property, Plant and Equipment (Topic 360): Reporting Discontinued Operations and disclosures of Components of an Entity.” Under this guidance, only disposals representing a strategic shift in operations should be presented as discontinued operations. The guidance also requires new disclosures of both discontinued operations and certain other disposals that do not meet the definition of a discontinued operation. The Company adopted this guidance effective January 1, 2015. The Company has not previously had discontinued operations and as such, does not expect this guidance to have a significant impact on its consolidated financial statements.
	In May 2014, the FASB issued ASU 2014-09, “Revenue from Contracts with Customers,” which amends the guidance for revenue recognition to replace numerous, industry-specific requirements and converges areas under this topic with those of the International Financial Reporting Standards. ASU 2014-09 outlines a five-step process for customer contract revenue recognition that focuses on transfer of control, as opposed to transfer of risk and rewards. The amendment also requires enhanced disclosures regarding the nature, amount, timing and uncertainty of revenues and cash flows from contracts with customers. ASU 2014-09 is effective for reporting periods beginning after December 15, 2016, and early adoption is prohibited. Entities can transition to the standard either retrospectively or as a cumulative-effect adjustment as of the date of adoption. Management is currently assessing the impact of the adoption of ASU 2014-09 on the Company’s condensed consolidated financial statements.
	In June 2014, the FASB issued ASU 2014-12, “Accounting for Share-Based Payments When the Terms of an Award Provide That a Performance Target Could Be Achieved after the Requisite Service Period,” which requires a reporting entity to treat a performance target that affects vesting, and that could be achieved after the requisite service period, as a performance condition. ASU 2014-12 is effective for annual periods, and interim periods within those annual periods, beginning after December 15, 2015. Early adoption is permitted. ASU 2014-12 may be adopted either prospectively for share-based payment awards granted or modified on or after the effective date, or retrospectively, using a modified retrospective approach. The modified retrospective approach would apply to share-based payment awards outstanding as of the beginning of the earliest annual period presented in the financial statements on adoption, and to all new or modified awards thereafter. The Company does not expect the adoption of ASU 2014-12 to have a material impact on its consolidated financial statements.
	In February 2015, the FASB issued ASU 2015-02, “Consolidation (Topic 810): Amendments to the Consolidation Analysis.” This guidance is effective for annual reporting periods beginning after December 15, 2015, including interim periods within that reporting period. ASU 2015-02 amends the criteria for determining if a service provider possesses a variable interest in a VIE, and eliminates the presumption that a general partner should consolidate a limited partnership. The Company does not expect the adoption of this standard to materially impact its consolidated financial statements.
	In April 2015, the FASB issued ASU 2015-03, “Interest—Imputation of Interest: Simplifying the Presentation of Debt Issuance Costs.” This guidance requires debt issuance costs related to a recognized debt liability to be presented as a direct deduction from the carrying amount of that debt liability. The new guidance will only impact financial statement presentation. The guidance is effective in the first quarter of 2016 and allows for early adoption. The Company does not expect the adoption of this standard to materially impact its consolidated financial statements.

Fair_Value_Disclosures

Fair Value Disclosures	3 Months Ended
	Mar. 31, 2015
Fair Value Disclosures [Abstract]
Fair Value Disclosures	3. FAIR VALUE DISCLOSURES
	Derivative Financial Instruments
	Currently, the Company uses interest rate swaps to manage its interest rate risk. The valuation of these instruments is determined using widely accepted valuation techniques, including discounted cash flow analysis on the expected cash flows of each derivative. This analysis reflects the contractual terms of the derivatives, including the period to maturity, and uses observable market-based inputs, including interest rate curves. The fair values of interest rate swaps are determined using the market standard methodology of netting the discounted future fixed cash payments and the discounted expected variable cash receipts. The variable cash receipts are based on an expectation of future interest rates (forward curves) derived from observable market interest rate forward curves.
	The Company incorporates credit valuation adjustments to appropriately reflect both its own nonperformance risk and the respective counterparty’s nonperformance risk in the fair value measurements. In adjusting the fair value of its derivative contracts for the effect of nonperformance risk, the Company has considered the impact of netting and any applicable credit enhancements, such as collateral postings, thresholds, mutual puts and guarantees. In conjunction with the Financial Accounting Standards Board’s fair value measurement guidance, the Company made an accounting policy election to measure the credit risk of its derivative financial instruments that are subject to master netting agreements on a net basis by counterparty portfolio.
	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, the credit valuation adjustments associated with its derivatives utilize Level 3 inputs, such as estimates of current credit spreads to evaluate the likelihood of default by the Company and its counterparties. However, as of March 31, 2015, the Company had assessed the significance of the impact of the credit valuation adjustments on the overall valuation of its derivative positions and determined that the credit valuation adjustments were not significant to the overall valuation of its derivatives. As a result, the Company determined that its derivative valuations in their entirety were classified in Level 2 of the fair value hierarchy.
	The table below presents the Company’s assets and liabilities measured at fair value on a recurring basis as of March 31, 2015, aggregated by the level in the fair value hierarchy within which those measurements fall.
		March 31,			Fair Value Measurements at Reporting Date Using
	Description	2015			Quoted Prices in		Significant Other			Significant
					Active Markets		Observable			Unobservable
					for Identical		Inputs (Level 2)			Inputs (Level 3)
					Assets (Level 1)
	Other assets—Cash Flow Hedge Swap Agreements	$	688		$	—	$	688		$	—
	Other liabilities—Cash Flow Hedge Swap Agreements	$	(7,231	)	$	—	$	(7,231	)	$	—
	There were no transfers of assets and liabilities between Level 1 and Level 2 during the three months ended March 31, 2015. The Company did not have any significant assets or liabilities that are re-measured on a recurring basis using significant unobservable inputs as of March 31, 2015 or December 31, 2014.
	Assets and Liabilities Measured at Fair Value on a Nonrecurring Basis
	Long-lived assets held for use are evaluated for impairment when events or circumstances indicate there may be impairment. The Company reviews each store at least annually to determine if any such events or circumstances have occurred or exist. The Company focuses on stores where occupancy and/or rental income have decreased by a significant amount. For these stores, the Company determines whether the decrease is temporary or permanent, and whether the store will likely recover the lost occupancy and/or revenue in the short term. In addition, the Company carefully reviews stores in the lease-up stage and compares actual operating results to original projections.
	When the Company determines that an event that may indicate impairment has occurred, the Company compares the carrying value of the related long-lived assets to the undiscounted future net operating cash flows attributable to the assets. An impairment loss is recorded if the net carrying value of the assets exceeds the undiscounted future net operating cash flows attributable to the assets. The impairment loss recognized equals the excess of net carrying value over the related fair value of the assets.
	When real estate assets are identified by management as held for sale, the Company discontinues depreciating the assets and estimates the fair value of the assets, net of selling costs. If the estimated fair value, net of selling costs, of the assets that have been identified as held for sale is less than the net carrying value of the assets, a valuation allowance is established. The operations of assets held for sale or sold during the period are presented as part of normal operations for all periods presented.
	The Company assesses whether there are any indicators that the value of the Company’s investments in unconsolidated real estate ventures may be impaired annually and when events or circumstances indicate that there may be impairment. An investment is impaired if management’s estimate of the fair value of the investment is less than its carrying value. To the extent impairment has occurred, and is considered to be other than temporary, the loss is measured as the excess of the carrying amount of the investment over the fair value of the investment.
	In connection with the Company’s acquisition of stores, the purchase price is allocated to the tangible and intangible assets and liabilities acquired based on their fair values, which are estimated using significant unobservable inputs. The value of the tangible assets, consisting of land and buildings, is determined as if vacant. Intangible assets, which represent the value of existing tenant relationships, are recorded at their fair values based on the avoided cost to replace the current leases. The Company measures the value of tenant relationships based on the rent lost due to the amount of time required to replace existing customers, which is based on the Company’s historical experience with turnover in its stores. Debt assumed as part of an acquisition is recorded at fair value based on current interest rates compared to contractual rates. Acquisition-related transaction costs are expensed as incurred.
	Fair Value of Financial Instruments
	The carrying values of cash and cash equivalents, restricted cash, receivables, other financial instruments included in other assets, accounts payable and accrued expenses, variable-rate notes payable, lines of credit and other liabilities reflected in the condensed consolidated balance sheets at March 31, 2015 and December 31, 2014 approximate fair value.
	The fair values of the Company’s notes receivable from Preferred Operating Partnership unit holders were based on the discounted estimated future cash flows of the notes (categorized within Level 3 of the fair value hierarchy); the discount rate used approximated the current market rate for loans with similar maturities and credit quality. The fair values of the Company’s fixed-rate notes payable and notes payable to trusts were estimated using the discounted estimated future cash payments to be made on such debt (categorized within Level 3 of the fair value hierarchy); the discount rates used approximated current market rates for loans, or groups of loans, with similar maturities and credit quality. The fair value of the Company’s exchangeable senior notes was estimated using an average market price for similar securities obtained from a third party.
	The fair values of the Company’s fixed-rate assets and liabilities were as follows for the periods indicated:
		March 31, 2015					December 31, 2014
		Fair			Carrying		Fair			Carrying
		Value			Value		Value			Value
	Notes receivable from Preferred Operating Partnership unit holders	$	129,102		$	120,230	$	126,380		$	120,230
	Fixed rate notes payable and notes payable to trusts	$	1,487,014		$	1,438,400	$	1,320,370		$	1,283,893
	Exchangeable senior notes	$	310,625		$	250,000	$	276,095		$	250,000

Earnings_Per_Common_Share

Earnings Per Common Share	3 Months Ended
	Mar. 31, 2015
Earnings Per Share [Abstract]
Earnings Per Common Share	4. EARNINGS PER COMMON SHARE
	Basic earnings per common share is computed using the two-class method by dividing net income attributable to common stockholders by the weighted average number of common shares outstanding during the period. All outstanding unvested restricted stock awards contain rights to non-forfeitable dividends and participate in undistributed earnings with common stockholders; accordingly, they are considered participating securities that are included in the two-class method. Diluted earnings per common share measures the performance of the Company over the reporting period while giving effect to all potential common shares that were dilutive and outstanding during the period. The denominator includes the weighted average number of basic shares and the number of additional common shares that would have been outstanding if the potential common shares that were dilutive had been issued, and is calculated using either the two-class, treasury stock or as if-converted method, whichever is most dilutive. Potential common shares are securities (such as options, convertible debt, Series A Participating Redeemable Preferred Units (“Series A Units”), Series B Redeemable Preferred Units (“Series B Units”), Series C Convertible Redeemable Preferred Units (“Series C Units”), Series D Redeemable Preferred Units (“Series D Units”) and common Operating Partnership units (“OP Units”)) that do not have a current right to participate in earnings of the Company but could do so in the future by virtue of their option, redemption or conversion right.
	In computing the dilutive effect of convertible securities, net income is adjusted to add back any changes in earnings in the period associated with the convertible security. The numerator also is adjusted for the effects of any other non-discretionary changes in income or loss that would result from the assumed conversion of those potential common shares. In computing diluted earnings per common share, only potential common shares that are dilutive (those that reduce earnings per common share) are included. For the three months ended March 31, 2015 and 2014, options to purchase approximately 19,762 and 18,100 shares of common stock, respectively, were excluded from the computation of earnings per share as their effect would have been anti-dilutive.
	The following table presents the number of Preferred Operating Partnership units, and the potential common shares, that were excluded from the computation of earnings per share as their effect would have been anti-dilutive, assuming full conversion at the average share price for the quarter of $65.59.
		For the Three Months Ended March 31,
		2015						2014
		Number of			Equivalent			Number of		Equivalent
		Units			Shares			Units		Shares
					(if converted)					(if converted)
	Series B Units		1,676,087			638,850			1,342,727		724,232
	Series C Units		704,016			451,884			407,996		370,585
	Series D Units		548,390			209,022			—		—
			2,928,493			1,299,756			1,750,723		1,094,817
	The Operating Partnership had $250,000 of its 2.375% Exchangeable Senior Notes due 2033 (the “Notes”) issued and outstanding as of March 31, 2015. The Notes could potentially have a dilutive impact on the Company’s earnings per share calculations. The Notes are exchangeable by holders into shares of the Company’s common stock under certain circumstances per the terms of the indenture governing the Notes. The exchange price of the Notes was $55.62 per share as of March 31, 2015, and could change over time as described in the indenture. The Company has irrevocably agreed to pay only cash for the accreted principal amount of the Notes relative to its exchange obligations, but retained the right to satisfy the exchange obligation in excess of the accreted principal amount in cash and/or common stock.
	Though the Company has retained that right, Accounting Standards Codification (“ASC”) 260, “Earnings per Share,” requires an assumption that shares would be used to pay the exchange obligation in excess of the accreted principal amount, and requires that those shares be included in the Company’s calculation of weighted average common shares outstanding for the diluted earnings per share computation. For the three months ended March 31, 2015, 682,502 shares related to the Notes were included in the computation for diluted earnings per share. For the three months ended March 31, 2014, no shares related to the Notes were included in the computation for diluted earnings per share as the exchange price exceeded the per share price of the Company’s common stock during this period.
	For the purposes of computing the diluted impact on earnings per share of the potential exchange of Series A Units for common shares upon redemption, where the Company has the option to redeem in cash or shares and where the Company has stated the positive intent and ability to settle at least $115,000 of the instrument in cash (or net settle a portion of the Series A Units against the related outstanding note receivable), only the amount of the instrument in excess of $115,000 is considered in the calculation of shares contingently issuable for the purposes of computing diluted earnings per share as allowed by ASC 260-10-45-46.
	For the purposes of computing the diluted impact on earnings per share of the potential exchange of Series B Units for common shares upon redemption, where the Company has the option to redeem in cash or shares and where the Company has stated the intent and ability to settle the redemption in shares, the Company divided the total value of the Series B Units outstanding as of March 31, 2015 of $41,902 by the closing price of the Company’s common stock as of March 31, 2015 of $67.57 per share. Assuming full exchange for common shares as of March 31, 2015, 620,127 shares would have been issued to the holders of the Series B Units.
	For the purposes of computing the diluted impact on earnings per share of the potential exchange of Series C Units for common shares upon redemption, where the Company has the option to redeem in cash or shares and where the Company has stated the intent and ability to settle the redemption in shares, the Company divided the total value of the Series C Units outstanding as of March 31, 2015 of $29,639 by the closing price of the Company’s common stock as of March 31, 2015 of $67.57 per share. Assuming full exchange for common shares as of March 31, 2015, 438,641 shares would have been issued to the holders of the Series C Units.
	For the purposes of computing the diluted impact on earnings per share of the potential exchange of Series D Units for common shares upon redemption, where the Company has the option to redeem in cash or shares and where the Company has stated the intent and ability to settle the redemption in shares, the Company divided the total value of the Series D Units outstanding as of March 31, 2015 of $13,710 by the closing price of the Company’s common stock as of March 31, 2015 of $67.57 per share. Assuming full exchange for common shares as of March 31, 2015, 202,901 shares would have been issued to the holders of Series D Units.
	The computation of earnings per common share was as follows for the periods presented:
		For the Three Months Ended
		March 31,
		2015			2014
	Net income attributable to common stockholders	$	53,742		$	37,340
	Earnings and dividends allocated to participating securities		(119	)		(117	)
	Earnings for basic computations		53,623			37,223
	Earnings and dividends allocated to participating securities		119			—
	Income allocated to noncontrolling interest—Preferred Operating Partnership (Series A Units) and Operating Partnership		3,635			3,128
	Fixed component of income allocated to noncontrolling interest—Preferred Operating Partnership (Series A Units)		(1,274	)		(1,438	)
	Net income for diluted computations	$	56,103		$	38,913
	Weighted average common shares outstanding:
	Average number of common shares outstanding—basic		116,117,615			115,438,325
	Series A Units		875,480			989,980
	OP Units		4,365,879			4,334,118
	Unvested restricted stock awards included for treasury stock method		282,903			—
	Shares related to exchangeable senior notes and dilutive stock options		953,841			300,422
	Average number of common shares outstanding—diluted		122,595,718			121,062,845
	Earnings per common share
	Basic	$	0.46		$	0.32
	Diluted	$	0.46		$	0.32

Store_Acquisitions

Store Acquisitions	3 Months Ended
	Mar. 31, 2015
Business Combinations [Abstract]
Store Acquisitions	5. STORE ACQUISITIONS
	The following table summarizes the Company’s acquisitions of operating stores for the three months ended March 31, 2015, and does not include purchases of raw land or improvements made to existing assets:
			Number		Date of		Consideration Paid														Acquisition Date Fair Value
			of		Acquisition
	Property Location		Stores				Total		Cash		Non-cash		Notes		Previous			Net			Land		Building		Intangible		Closing costs—
									Paid		gain		Receivable		equity			Liabilities/(Assets)									expensed (1)
															interest			Assumed
	California (2)			1		3/30/15	$	12,699	$	1,700	$	1,629	$	11,009	$	(1,264	)	$	(375	)	$	1,025	$	11,479	$	195	$	—
	North Carolina, South Carolina			2		3/30/15		13,165		13,143		—		—		—			22			1,763		11,229		144		29
	Virginia			1		3/17/15		5,073		5,065		—		—		—			8			118		4,797		81		77
	Texas			1		2/24/15		13,570		13,519		—		—		—			51			1,511		11,861		182		16
	Texas			3		1/13/15		41,904		41,806		—		—		—			98			12,080		29,489		300		35
	2015 Totals			8			$	86,411	$	75,233	$	1,629	$	11,009	$	(1,264	)	$	(196	)	$	16,497	$	68,855	$	902	$	157
	-1	This column represents costs paid at closing. The amounts shown exclude other acquisition costs paid before or after the closing date.
	-2	This represents the acquisition of a joint venture partners’ interest in Extra Space of Sacramento One LLC (“Sacramento One”), an existing joint venture, for $1,700 in cash. The result of the acquisition is that the Company owns 100% of Sacramento One, which owned one store located in California. Prior to the acquisition date, the Company accounted for its interest in Sacramento One as an equity-method investment, and the Company also held mortgage notes receivable from Sacramento One totalling $11,009, including related interest. The total acquisition date fair value of the Company’s previous equity interest was approximately $365 and is included in consideration transfered. The Company recognized a non-cash gain of $1,629 as a result of remeasuring the fair value of its equity interest held prior to the acquisition. The store is consolidated subsequent to the acquisition as the Company owns 100% of the store.

Variable_Interests

Variable Interests	3 Months Ended
	Mar. 31, 2015
Equity Method Investments and Joint Ventures [Abstract]
Variable Interests	6. VARIABLE INTERESTS
	The Operating Partnership has three wholly-owned unconsolidated subsidiaries (“Trust,” “Trust II” and “Trust III,” together, the “Trusts”) that have issued trust preferred securities to third parties and common securities to the Operating Partnership. The proceeds from the sale of the preferred and common securities were loaned in the form of notes to the Operating Partnership. The Trusts are VIEs because the holders of the equity investment at risk (the trust preferred securities) do not have the power to direct the activities of the entities that most significantly affect the entities’ economic performance because of their lack of voting or similar rights. Because the Operating Partnership’s investment in the Trusts’ common securities was financed directly by the Trusts as a result of its loan of the proceeds to the Operating Partnership, that investment is not considered an equity investment at risk. The Operating Partnership’s investment in the Trusts is not a variable interest because equity interests are variable interests only to the extent that the investment is considered to be at risk, and therefore the Operating Partnership cannot be the primary beneficiary of the Trusts. Since the Company is not the primary beneficiary of the Trusts, they have not been consolidated. A debt obligation has been recorded in the form of notes for the proceeds as discussed above, which are owed to the Trusts. The Company has also included its investment in the Trusts’ common securities in other assets on the condensed consolidated balance sheets.
	The Company has not provided financing or other support during the periods presented to the Trusts that it was not previously contractually obligated to provide. The Company’s maximum exposure to loss as a result of its involvement with the Trusts is equal to the total amount of the notes discussed above less the amounts of the Company’s investments in the Trusts’ common securities. The net amount is the notes payable that the Trusts owe to third parties for their investments in the Trusts’ preferred securities.
	Following is a tabular comparison of the liabilities the Company has recorded as a result of its involvement with the Trusts to the maximum exposure to loss the Company is subject to as a result of such involvement as of March 31, 2015:
		Notes		Investment		Maximum		Difference
		payable		Balance		exposure
		to Trusts				to loss
	Trust	$	36,083	$	1,083	$	35,000	$	—
	Trust II		42,269		1,269		41,000		—
	Trust III		41,238		1,238		40,000		—
		$	119,590	$	3,590	$	116,000	$	—
	The Company had no consolidated VIEs during the three months ended March 31, 2015.

Derivatives

Derivatives	3 Months Ended
	Mar. 31, 2015
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivatives	7. DERIVATIVES
	The Company is exposed to certain risks arising from both its business operations and economic conditions. The Company principally manages its exposures to a wide variety of business and operational risks through management of its core business activities. The Company manages economic risks, including interest rate, liquidity and credit risk, primarily by managing the amount, sources and duration of its debt funding and by using derivative financial instruments. Specifically, the Company enters into derivative financial instruments to manage exposure that arises from business activities that result in the receipt or payment of future known and uncertain cash amounts, the value of which are determined by interest rates. The Company’s derivative financial instruments are used to manage differences in the amount, timing and duration of the Company’s known or expected cash receipts and its known or expected cash payments principally related to the Company’s investments and borrowings.
	Cash Flow Hedges of Interest Rate Risk
	The Company’s objectives in using interest rate derivatives are to add stability to interest expense and to manage its exposure to interest rate movements. To accomplish these objectives, the Company primarily uses interest rate swaps as part of its interest rate risk management strategy. Interest rate swaps designated as cash flow hedges involve the receipt of variable amounts from a counterparty in exchange for the Company making fixed-rate payments over the life of the agreements without exchange of the underlying notional amount.
	The effective portion of changes in the fair value of derivatives designated and that qualify as cash flow hedges is recorded in accumulated other comprehensive income (“OCI”) and is subsequently reclassified into earnings in the period that the hedged forecasted transaction affects earnings. A portion of these changes is excluded from accumulated other comprehensive income as it is allocated to noncontrolling interests. During the three months ended March 31, 2015 and 2014, such derivatives were used to hedge the variable cash flows associated with existing variable-rate debt.
	The Company held 23 derivative financial instruments which had a total combined notional amount of $825,987 as of March 31, 2015.
	Fair Values of Derivative Instruments
	The table below presents the fair value of the Company’s derivative financial instruments as well as their classification on the condensed consolidated balance sheets:
		Asset (Liability) Derivatives
		March 31,				December 31,
		2015				2014
	Derivatives designated as hedging instruments:
	Other assets	$	688			$	3,583
	Other liabilities	$	(7,231	)		$	(3,533	)
	Effect of Derivative Instruments
	The tables below present the effect of the Company’s derivative financial instruments on the condensed consolidated statements of operations for the periods presented. No tax effect has been presented as the derivative instruments are held by the Company:
		Classification of		For the Three Months
		Income (Expense)		Ended March 31,
	Type			2015				2014
	Swap Agreements	Interest expense		$	(2,297	)		$	(2,293	)
		Gain (loss)								Location of	Gain (loss)
		recognized in OCI								amounts	reclassifed from
		March 31,								reclassified from	OCI
										OCI into income	For the Three
											Months Ended
											March 31,
	Type	2015				2014					2015			2014
	Swap Agreements	$	(8,875	)		$	(5,043	)		Interest expense	$	(2,297	)	$	(2,293	)
	Credit-risk-related Contingent Features
	The Company has agreements with some of its derivative counterparties that contain provisions pursuant to which the Company could be declared in default of its derivative obligations if the Company defaults on any of its indebtedness, including default where repayment of the indebtedness has not been accelerated by the lender.
	The Company also has an agreement with some of its derivative counterparties that incorporates the loan covenant provisions of the Company’s indebtedness with a lender affiliate of the derivative counterparty. Failure to comply with the loan covenant provisions would result in the Company being in default on any derivative instrument obligations covered by the agreement.
	As of March 31, 2015, the Company had not posted any collateral related to these agreements. If the Company had breached any of these provisions as of March 31, 2015, it could have been required to settle its obligations under the agreements at their termination value of $7,740, including accrued interest.

Exchangeable_Senior_Notes

Exchangeable Senior Notes	3 Months Ended
	Mar. 31, 2015
Text Block [Abstract]
Exchangeable Senior Notes	8. EXCHANGEABLE SENIOR NOTES
	On June 21, 2013, the Operating Partnership issued $250,000 of its 2.375% Exchangeable Senior Notes due 2033 at a 1.5% discount, or $3,750. Costs incurred to issue the Notes were approximately $1,672. These costs are being amortized as an adjustment to interest expense over five years, which represents the estimated term based on the first available redemption date, and are included in other assets in the condensed consolidated balance sheets. The Notes are general unsecured senior obligations of the Operating Partnership and are fully guaranteed by the Company. Interest is payable on January 1 and July 1 of each year beginning January 1, 2014, until the maturity date of July 1, 2033. The Notes bear interest at 2.375% per annum and contain an exchange settlement feature, which provides that the Notes may, under certain circumstances, be exchangeable for cash (for the principal amount of the Notes) and, with respect to any excess exchange value, for cash, shares of the Company’s common stock, or a combination of cash and shares of the Company’s common stock, at the Company’s option. The exchange rate of the Notes as of March 31, 2015 was approximately 17.98 shares of the Company’s common stock per $1,000 principal amount of the Notes.
	The Operating Partnership may redeem the Notes at any time to preserve the Company’s status as a REIT. In addition, on or after July 5, 2018, the Operating Partnership may redeem the Notes for cash, in whole or in part, at 100% of the principal amount plus accrued and unpaid interest, upon at least 30 days but not more than 60 days prior written notice to the holders of the Notes. The holders of the Notes have the right to require the Operating Partnership to repurchase the Notes for cash, in whole or in part, on July 1 of the years 2018, 2023 and 2028, and upon the occurrence of certain designated events, in each case for a repurchase price equal to 100% of the principal amount of the Notes plus accrued and unpaid interest. Certain events are considered “Events of Default,” as defined in the indenture governing the Notes, which may result in the accelerated maturity of the Notes.
	GAAP requires entities with convertible debt instruments that may be settled entirely or partially in cash upon conversion to separately account for the liability and equity components of the instrument in a manner that reflects the issuer’s economic interest cost. The Company therefore accounts for the liability and equity components of the Notes separately. The equity component is included in additional paid-in capital in stockholders’ equity in the condensed consolidated balance sheets, and the value of the equity component is treated as original issue discount for purposes of accounting for the debt component. The discount is being amortized as interest expense over the remaining period of the debt through its first redemption date, July 1, 2018. The effective interest rate on the liability component is 4.0%.
	Information about the carrying amount of the equity component, the principal amount of the liability component, its unamortized discount and its net carrying amount was as follows for the periods indicated:
		March 31,			December 31,
		2015			2014
	Carrying amount of equity component	$	14,496		$	14,496
	Principal amount of liability component	$	250,000		$	250,000
	Unamortized discount—equity component		(9,751	)		(10,448	)
	Unamortized cash discount		(2,418	)		(2,606	)
	Net carrying amount of liability component	$	237,831		$	236,946
	The amount of interest cost recognized relating to the contractual interest rate and the amortization of the discount on the liability component of the Notes were as follows for the periods indicated:
		For the Three
		Months Ended
		March 31,
		2015			2014
	Contractual interest	$	1,484		$	1,484
	Amortization of discount		697			662
	Total interest expense recognized	$	2,181		$	2,146

Noncontrolling_Interests

Noncontrolling Interests	3 Months Ended
	Mar. 31, 2015
Noncontrolling Interests	11. OTHER NONCONTROLLING INTERESTS
	Other noncontrolling interests represent the ownership interests of various third parties in two consolidated joint ventures as of March 31, 2015. One of these consolidated joint ventures owns a single store in California. The second consolidated joint venture owns 19 stores. The ownership interests of the third-party owners range from 1.0% to 3.3%. Other noncontrolling interests are included in the stockholders’ equity section of the Company’s condensed consolidated balance sheets. The income or losses attributable to these third-party owners based on their ownership percentages are reflected in net income allocated to Operating Partnership and other noncontrolling interests in the condensed consolidated statements of operations.
Preferred Operating Partnership Units [Member]
Noncontrolling Interests	9. NONCONTROLLING INTEREST REPRESENTED BY PREFERRED OPERATING PARTNERSHIP UNITS
	Classification of Noncontrolling Interests
	GAAP requires a company to present ownership interests in subsidiaries held by parties other than the company in the consolidated financial statements within the equity section, but separate from the company’s equity. It also requires the amount of consolidated net income attributable to the parent and to the noncontrolling interest to be clearly identified and presented on the face of the consolidated statement of operations and requires changes in ownership interest to be accounted for similarly as equity transactions. If noncontrolling interests are determined to be redeemable, they are to be carried at their redemption value as of the balance sheet date and reported as temporary equity.
	The Company has evaluated the terms of the Operating Partnership’s preferred units and classifies the noncontrolling interest represented by such preferred units as stockholders’ equity in the accompanying condensed consolidated balance sheets. The Company will periodically evaluate individual noncontrolling interests for the ability to continue to recognize the noncontrolling interest as permanent equity in the condensed consolidated balance sheets. Any noncontrolling interests that fail to qualify as permanent equity will be reclassified as temporary equity and adjusted to the greater of (1) the carrying amount and (2) the redemption value as of the end of the period in which the determination is made.
	Series A Participating Redeemable Preferred Units
	On June 15, 2007, the Operating Partnership entered into a Contribution Agreement with various limited partnerships affiliated with AAAAA Rent-A-Space to acquire ten stores in exchange for 989,980 Series A Units of the Operating Partnership. The stores are located in California and Hawaii.
	On June 25, 2007, the Operating Partnership loaned the holders of the Series A Units $100,000. The note receivable bears interest at 4.85% per annum. During 2013, a loan amendment was signed extending the maturity date to September 1, 2020. The loan is secured by the borrower’s Series A Units. The holders of the Series A Units could redeem up to 114,500 Series A Units prior to the maturity date of the loan. If any redemption in excess of 114,500 Series A Units occurs prior to the maturity date, the holder of the Series A Units is required to repay the loan as of the date of that redemption.
	The partnership agreement of the Operating Partnership (as amended, the “Partnership Agreement”) provides for the designation and issuance of the Series A Units. The Series A Units will have priority over all other partnership interests of the Operating Partnership with respect to distributions and liquidation.
	Under the Partnership Agreement, Series A Units in the amount of $115,000 bear a fixed priority return of 5% and have a fixed liquidation value of $115,000. The remaining balance participates in distributions with, and has a liquidation value equal to, that of the OP Units. The Series A Units are redeemable at the option of the holder, which redemption obligation may be satisfied, at the Company’s option, in cash or shares of its common stock.
	On October 3, 2014, the holders of the Series A Units redeemed 114,500 Series A Units for $4,794 in cash and 280,331 shares of common stock. No additional redemption of Series A Units can be made without repayment of the loan. Subsequent to this redemption, the fixed priority return is calculated using the current liquidation value of $101,699. The Series A Units are shown on the balance sheet net of the $100,000 loan because the borrower under the loan receivable is also the holder of the Series A Units.
	Series B Redeemable Preferred Units
	On April 3, 2014, the Operating Partnership completed the purchase of a store located in Georgia. This store was acquired in exchange for $15,158 of cash and 333,360 Series B Units valued at $8,334.
	On August 29, 2013, the Operating Partnership completed the purchase of 19 out of 20 stores affiliated with All Aboard Mini Storage, all of which are located in California. On September 26, 2013, the Operating Partnership completed the purchase of the remaining store. These stores were acquired in exchange for $100,876 of cash (including $98,960 of debt assumed and immediately defeased at closing), 1,342,727 Series B Units valued at $33,568, and 1,448,108 OP Units valued at $62,341.
	The Partnership Agreement provides for the designation and issuance of the Series B Units. The Series B Units rank junior to the Series A Units, on parity with the Series C Units, and senior to all other partnership interests of the Operating Partnership with respect to distributions and liquidation.
	The outstanding Series B Units have a liquidation value of $25.00 per unit for a fixed liquidation value of $41,902. Holders of the Series B Units receive distributions at an annual rate of 6%. These distributions are cumulative. The Series B Units will become redeemable at the option of the holder on the first anniversary of the date of issuance, which redemption obligation may be satisfied at the Company’s option in cash or shares of its common stock.
	Series C Convertible Redeemable Preferred Units
	On November 19, 2013, the Company entered into Contribution Agreements with various entities affiliated with Grupe Properties Co. Inc. (“Grupe”), under which the Company agreed to acquire twelve stores, all of which are located in California. The Company completed the purchase of these stores between December 2013 and May 2014. The Company previously held 35% interests in five of these stores and a 40% interest in one store through six separate joint ventures with Grupe. These stores were acquired in exchange for a total of approximately $45,722 of cash, the assumption of $37,532 in existing debt, and the issuance of 704,016 Series C Units valued at $30,960.
	The Partnership Agreement provides for the designation and issuance of the Series C Units. The Series C Units rank junior to the Series A Units, on parity with the Series B Units, and senior to all other partnership interests of the Operating Partnership with respect to distributions and liquidation.
	The outstanding Series C Units have a liquidation value of $42.10 per unit for a fixed liquidation value of $29,639. From issuance to the fifth anniversary of issuance, each Series C Unit holder will receive quarterly distributions equal to the quarterly distribution per OP Unit plus $0.18. Beginning on the fifth anniversary of issuance, each Series C Unit holder will receive a fixed quarterly distribution equal to the aggregate quarterly distribution payable in respect of such Series C Unit during the four quarters immediately preceding the fifth anniversary of issuance, divided by four. These distributions are cumulative. The Series C Units will become redeemable at the option of the holder one year from the date of issuance, which redemption obligation may be satisfied at the Company’s option in cash or shares of its common stock. The Series C Units will also become convertible into OP Units at the option of the holder one year from the date of issuance, at a rate of 0.9145 OP Units per Series C Unit converted. This conversion option expires upon the fifth anniversary of the date of issuance.
	In December 2014, the Operating Partnership loaned certain holders of the Series C Units $20,230. The notes receivable, which are collateralized by the Series C Units, bear interest at 5.0% per annum and mature on December 15, 2024. The Series C Units are shown on the balance sheet net of the $20,230 loan because the borrower under the loan receivable is also the holder of the Series C units.
	Series D Redeemable Preferred Units
	In December 2014, the Operating Partnership completed the acquisition of a store located in Florida. This store was acquired in exchange for $5,621 in cash and 548,390 Series D Units valued at $13,710.
	The Partnership Agreement provides for the designation and issuance of the Series D Units. The Series D Units rank junior to the Series A Units, on parity with the Series B Units and Series C Units, and senior to all other partnership interests of the Operating Partnership with respect to distributions and liquidation.
	The Series D Units have a liquidation value of $25.00 per unit, for a fixed liquidation value of $13,710. Holders of the Series D Units receive distributions at an annual rate of 5.0%. These distributions are cumulative. The Series D Units will become redeemable at the option of the holder on the first anniversary of the date of issuance, which redemption obligation may be satisfied at the Company’s option in cash or shares of its common stock.
Common Operating Partnership [Member]
Noncontrolling Interests	10. NONCONTROLLING INTEREST IN OPERATING PARTNERSHIP
	The Company’s interest in its stores is held through the Operating Partnership. ESS Holding Business Trust I, a wholly-owned subsidiary of the Company, is the sole general partner of the Operating Partnership. ESS Holding Business Trust II, also a wholly-owned subsidiary of the Company, is a limited partner of the Operating Partnership. Between its general partner and limited partner interests, the Company held a 93.4% ownership interest in the Operating Partnership as of March 31, 2015. The remaining ownership interests in the Operating Partnership (including Preferred Operating Partnership units) of 6.6% are held by certain former owners of assets acquired by the Operating Partnership.
	The noncontrolling interest in the Operating Partnership represents OP Units that are not owned by the Company. In conjunction with the formation of the Company, and as a result of subsequent acquisitions, certain persons and entities contributing interests in stores to the Operating Partnership received limited partnership interests in the form of OP Units. Limited partners who received OP Units in the formation transactions or in exchange for contributions for interests in stores have the right to require the Operating Partnership to redeem part or all of their OP Units for cash based upon the fair market value of an equivalent number of shares of the Company’s common stock (based on the ten-day average trading price) at the time of the redemption. Alternatively, the Company may, in its sole discretion, elect to acquire those OP Units in exchange for shares of its common stock on a one-for-one basis, subject to anti-dilution adjustments provided in the Partnership Agreement. The ten-day average closing stock price at March 31, 2015 was $67.76 and there were 4,365,879 OP Units outstanding. Assuming that all of the OP Unit holders exercised their right to redeem all of their OP Units on March 31, 2015 and the Company elected to pay the OP Unit holders cash, the Company would have paid $295,832 in cash consideration to redeem the units.
	GAAP requires a company to present ownership interests in subsidiaries held by parties other than the company in the consolidated financial statements within the equity section, but separate from the company’s equity. It also requires the amount of consolidated net income attributable to the parent and to the noncontrolling interest to be clearly identified and presented on the face of the consolidated statement of operations, and requires changes in ownership interest to be accounted for similarly as equity transactions. If noncontrolling interests are determined to be redeemable, they are to be carried at their redemption value as of the balance sheet date and reported as temporary equity.
	The Company has evaluated the terms of the OP Units and classifies the noncontrolling interest represented by the OP Units as stockholders’ equity in the accompanying condensed consolidated balance sheets. The Company will periodically evaluate individual noncontrolling interests for the ability to continue to recognize the noncontrolling amount as permanent equity in the condensed consolidated balance sheets. Any noncontrolling interests that fail to qualify as permanent equity will be reclassified as temporary equity and adjusted to the greater of (1) the carrying amount and (2) the redemption value as of the end of the period in which the determination is made.

Equity_in_Earnings_of_Unconsol

Equity in Earnings of Unconsolidated Real Estate Ventures - Gain on Sale of Real Estate and Purchase of Joint Venture Partners' Interests	3 Months Ended
	Mar. 31, 2015
Equity Method Investments and Joint Ventures [Abstract]
Equity in Earnings of Unconsolidated Real Estate Ventures - Gain on Sale of Real Estate and Purchase of Joint Venture Partners' Interests	12. EQUITY IN EARNINGS OF UNCONSOLIDATED REAL ESTATE VENTURES—GAIN ON SALE OF REAL ESTATE AND PURCHASE OF JOINT VENTURE PARTNERS’ INTERESTS
	In March 2015, ESS PRISA II LLC (“PRISA II”), a joint venture in which the Company holds a 2.0% interest, sold one store located in New York for $90,000. As a result of the sale, PRISA II recognized a gain of $60,496 and the Company recorded its 2.0% portion of the gain, or $1,228.
	In March 2015, the Company acquired its joint venture partner’s 82.4% interest in Sacramento One, an existing joint venture which owned one store located in California, for $1,700. In addition, the Company held mortgage notes receivable from Sacramento One totaling $11,009, which were eliminated as a result of the acquisition. Prior to the acquisition, the remaining 17.6% interest was owned by the Company, which accounted for its investment in Sacramento One using the equity method. The Company recorded a non-cash gain of $1,629 related to this transaction, which represents the increase in fair value of the company’s interest in the joint venture from its formation to the acquisition date.

Segment_Information

Segment Information	3 Months Ended
	Mar. 31, 2015
Segment Reporting [Abstract]
Segment Information	13. SEGMENT INFORMATION
	The Company operates in three distinct segments: (1) rental operations; (2) tenant reinsurance; and (3) property management, acquisition and development. Management fees collected for wholly-owned stores are eliminated in consolidation. Financial information for the Company’s business segments is presented below:
		March 31,			December 31,
		2015			2014
	Balance Sheet
	Investment in unconsolidated real estate ventures
	Rental operations	$	85,602		$	85,711
	Total assets
	Rental operations	$	4,194,744		$	4,109,673
	Tenant reinsurance		38,745			39,383
	Property management, acquisition and development		230,656			253,051
		$	4,464,145		$	4,402,107
		For the Three Months
		Ended March 31,
		2015			2014
	Statement of Operations
	Total revenues
	Rental operations	$	148,894		$	132,001
	Tenant reinsurance		16,510			13,463
	Property management, acquisition and development		7,750			7,123
			173,154			152,587
	Operating expenses, including depreciation and amortization
	Rental operations		75,509			69,942
	Tenant reinsurance		2,928			2,567
	Property management, acquisition and development		19,281			19,680
			97,718			92,189
	Income (loss) from operations
	Rental operations		73,385			62,059
	Tenant reinsurance		13,582			10,896
	Property management, acquisition and development		(11,531	)		(12,557	)
			75,436			60,398
	Interest expense
	Rental operations		(21,830	)		(19,310	)
	Property management, acquisition and development		399			(288	)
			(21,431	)		(19,598	)
	Non-cash interest expense related to the amortization of discount on equity component of exchangeable senior notes
	Property management, acquisition and development		(697	)		(662	)
	Interest income
	Tenant reinsurance		4			4
	Property management, acquisition and development		852			265
			856			269
	Interest income on note receivable from Preferred Operating Partnership unit holder
	Property management, acquisition and development		1,213			1,213
	Equity in earnings of unconsolidated real estate ventures
	Rental operations		2,650			2,419
	Equity in earnings of unconsolidated real estate ventures—gain on sale of real estate assets and purchase of partners’ interests
	Rental operations		2,857			—
	Income tax expense
	Rental operations		(754	)		(434	)
	Tenant reinsurance		(1,874	)		(3,815	)
	Property management, acquisition and development		380			1,419
			(2,248	)		(2,830	)
	Net income (loss)
	Rental operations		56,308			44,734
	Tenant reinsurance		11,712			7,085
	Property management, acquisition and development		(9,384	)		(10,610	)
		$	58,636		$	41,209
	Depreciation and amortization expense
	Rental operations	$	28,265		$	26,460
	Property management, acquisition and development		2,163			1,915
		$	30,428		$	28,375
	Statement of Cash Flows
	Acquisition of real estate assets
	Property management, acquisition and development	$	(77,082	)	$	(253,939	)
Development and redevelopment of real estate assets
Property management, acquisition and development	$	(3,140	)	$	(2,820	)

Commitments_and_Contingencies

Commitments and Contingencies	3 Months Ended
	Mar. 31, 2015
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	14. COMMITMENTS AND CONTINGENCIES
	As of March 31, 2015, the Company is involved in various legal proceedings and is subject to various claims and complaints arising in the ordinary course of business. In the opinion of management, such litigation, claims and complaints are not expected to have a material adverse effect on the Company’s financial condition or results of operations.
	As of March 31, 2015, the Company was under contract to acquire 42 stores for a total purchase price of $374,283. Of these 42 stores, 34 are scheduled to close in 2015. The remaining stores will close upon completion of construction, expected to occur on various dates in 2016 and 2017.

Subsequent_Events

Subsequent Events	3 Months Ended
	Mar. 31, 2015
Subsequent Events [Abstract]
Subsequent Events	15. SUBSEQUENT EVENTS
	On April 14, 2015, the Company purchased one store located in Texas for $8,650.
	On April 15, 2015, the Company purchased a portfolio of 22 stores located in Arizona and Texas for $177,700.
	On April 24, 2015, the Company purchased one store located in Georgia for $6,500.
	On May 5, 2015 the Company purchased one store located in North Carolina for $11,000.
	On May 7, 2015 the Company purchased another store located in Georgia for $6,500.

Basis_of_Presentation_Policies

Basis of Presentation (Policies)	3 Months Ended
	Mar. 31, 2015
Accounting Policies [Abstract]
Reclassifications	Reclassifications
	Certain amounts in the Company’s 2014 consolidated financial statements and supporting note disclosures have been reclassified to conform to the current period presentation. Such reclassifications did not impact previously reported net income or accumulated deficit.
Recently Issued Accounting Standards	Recently Issued Accounting Standards
	In April 2014, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) 2014-08, “Presentation of Financial Statements (Topic 205) and Property, Plant and Equipment (Topic 360): Reporting Discontinued Operations and disclosures of Components of an Entity.” Under this guidance, only disposals representing a strategic shift in operations should be presented as discontinued operations. The guidance also requires new disclosures of both discontinued operations and certain other disposals that do not meet the definition of a discontinued operation. The Company adopted this guidance effective January 1, 2015. The Company has not previously had discontinued operations and as such, does not expect this guidance to have a significant impact on its consolidated financial statements.
	In May 2014, the FASB issued ASU 2014-09, “Revenue from Contracts with Customers,” which amends the guidance for revenue recognition to replace numerous, industry-specific requirements and converges areas under this topic with those of the International Financial Reporting Standards. ASU 2014-09 outlines a five-step process for customer contract revenue recognition that focuses on transfer of control, as opposed to transfer of risk and rewards. The amendment also requires enhanced disclosures regarding the nature, amount, timing and uncertainty of revenues and cash flows from contracts with customers. ASU 2014-09 is effective for reporting periods beginning after December 15, 2016, and early adoption is prohibited. Entities can transition to the standard either retrospectively or as a cumulative-effect adjustment as of the date of adoption. Management is currently assessing the impact of the adoption of ASU 2014-09 on the Company’s condensed consolidated financial statements.
	In June 2014, the FASB issued ASU 2014-12, “Accounting for Share-Based Payments When the Terms of an Award Provide That a Performance Target Could Be Achieved after the Requisite Service Period,” which requires a reporting entity to treat a performance target that affects vesting, and that could be achieved after the requisite service period, as a performance condition. ASU 2014-12 is effective for annual periods, and interim periods within those annual periods, beginning after December 15, 2015. Early adoption is permitted. ASU 2014-12 may be adopted either prospectively for share-based payment awards granted or modified on or after the effective date, or retrospectively, using a modified retrospective approach. The modified retrospective approach would apply to share-based payment awards outstanding as of the beginning of the earliest annual period presented in the financial statements on adoption, and to all new or modified awards thereafter. The Company does not expect the adoption of ASU 2014-12 to have a material impact on its consolidated financial statements.
	In February 2015, the FASB issued ASU 2015-02, “Consolidation (Topic 810): Amendments to the Consolidation Analysis.” This guidance is effective for annual reporting periods beginning after December 15, 2015, including interim periods within that reporting period. ASU 2015-02 amends the criteria for determining if a service provider possesses a variable interest in a VIE, and eliminates the presumption that a general partner should consolidate a limited partnership. The Company does not expect the adoption of this standard to materially impact its consolidated financial statements.
	In April 2015, the FASB issued ASU 2015-03, “Interest—Imputation of Interest: Simplifying the Presentation of Debt Issuance Costs.” This guidance requires debt issuance costs related to a recognized debt liability to be presented as a direct deduction from the carrying amount of that debt liability. The new guidance will only impact financial statement presentation. The guidance is effective in the first quarter of 2016 and allows for early adoption. The Company does not expect the adoption of this standard to materially impact its consolidated financial statements.
Fair Value Disclosures	Derivative Financial Instruments
	Currently, the Company uses interest rate swaps to manage its interest rate risk. The valuation of these instruments is determined using widely accepted valuation techniques, including discounted cash flow analysis on the expected cash flows of each derivative. This analysis reflects the contractual terms of the derivatives, including the period to maturity, and uses observable market-based inputs, including interest rate curves. The fair values of interest rate swaps are determined using the market standard methodology of netting the discounted future fixed cash payments and the discounted expected variable cash receipts. The variable cash receipts are based on an expectation of future interest rates (forward curves) derived from observable market interest rate forward curves.
	The Company incorporates credit valuation adjustments to appropriately reflect both its own nonperformance risk and the respective counterparty’s nonperformance risk in the fair value measurements. In adjusting the fair value of its derivative contracts for the effect of nonperformance risk, the Company has considered the impact of netting and any applicable credit enhancements, such as collateral postings, thresholds, mutual puts and guarantees. In conjunction with the Financial Accounting Standards Board’s fair value measurement guidance, the Company made an accounting policy election to measure the credit risk of its derivative financial instruments that are subject to master netting agreements on a net basis by counterparty portfolio.
	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, the credit valuation adjustments associated with its derivatives utilize Level 3 inputs, such as estimates of current credit spreads to evaluate the likelihood of default by the Company and its counterparties. However, as of March 31, 2015, the Company had assessed the significance of the impact of the credit valuation adjustments on the overall valuation of its derivative positions and determined that the credit valuation adjustments were not significant to the overall valuation of its derivatives. As a result, the Company determined that its derivative valuations in their entirety were classified in Level 2 of the fair value hierarchy.
	The table below presents the Company’s assets and liabilities measured at fair value on a recurring basis as of March 31, 2015, aggregated by the level in the fair value hierarchy within which those measurements fall.
		March 31,			Fair Value Measurements at Reporting Date Using
	Description	2015			Quoted Prices in			Significant Other			Significant
					Active Markets			Observable			Unobservable
					for Identical			Inputs (Level 2)			Inputs (Level 3)
					Assets (Level 1)
	Other assets—Cash Flow Hedge Swap Agreements	$	688		$	—		$	688		$	—
	Other liabilities—Cash Flow Hedge Swap Agreements	$	(7,231	)	$	—		$	(7,231	)	$	—
	There were no transfers of assets and liabilities between Level 1 and Level 2 during the three months ended March 31, 2015. The Company did not have any significant assets or liabilities that are re-measured on a recurring basis using significant unobservable inputs as of March 31, 2015 or December 31, 2014.
	Assets and Liabilities Measured at Fair Value on a Nonrecurring Basis
	Long-lived assets held for use are evaluated for impairment when events or circumstances indicate there may be impairment. The Company reviews each store at least annually to determine if any such events or circumstances have occurred or exist. The Company focuses on stores where occupancy and/or rental income have decreased by a significant amount. For these stores, the Company determines whether the decrease is temporary or permanent, and whether the store will likely recover the lost occupancy and/or revenue in the short term. In addition, the Company carefully reviews stores in the lease-up stage and compares actual operating results to original projections.
	When the Company determines that an event that may indicate impairment has occurred, the Company compares the carrying value of the related long-lived assets to the undiscounted future net operating cash flows attributable to the assets. An impairment loss is recorded if the net carrying value of the assets exceeds the undiscounted future net operating cash flows attributable to the assets. The impairment loss recognized equals the excess of net carrying value over the related fair value of the assets.
	When real estate assets are identified by management as held for sale, the Company discontinues depreciating the assets and estimates the fair value of the assets, net of selling costs. If the estimated fair value, net of selling costs, of the assets that have been identified as held for sale is less than the net carrying value of the assets, a valuation allowance is established. The operations of assets held for sale or sold during the period are presented as part of normal operations for all periods presented.
	The Company assesses whether there are any indicators that the value of the Company’s investments in unconsolidated real estate ventures may be impaired annually and when events or circumstances indicate that there may be impairment. An investment is impaired if management’s estimate of the fair value of the investment is less than its carrying value. To the extent impairment has occurred, and is considered to be other than temporary, the loss is measured as the excess of the carrying amount of the investment over the fair value of the investment.
	In connection with the Company’s acquisition of stores, the purchase price is allocated to the tangible and intangible assets and liabilities acquired based on their fair values, which are estimated using significant unobservable inputs. The value of the tangible assets, consisting of land and buildings, is determined as if vacant. Intangible assets, which represent the value of existing tenant relationships, are recorded at their fair values based on the avoided cost to replace the current leases. The Company measures the value of tenant relationships based on the rent lost due to the amount of time required to replace existing customers, which is based on the Company’s historical experience with turnover in its stores. Debt assumed as part of an acquisition is recorded at fair value based on current interest rates compared to contractual rates. Acquisition-related transaction costs are expensed as incurred.
	Fair Value of Financial Instruments
	The carrying values of cash and cash equivalents, restricted cash, receivables, other financial instruments included in other assets, accounts payable and accrued expenses, variable-rate notes payable, lines of credit and other liabilities reflected in the condensed consolidated balance sheets at March 31, 2015 and December 31, 2014 approximate fair value.
	The fair values of the Company’s notes receivable from Preferred Operating Partnership unit holders were based on the discounted estimated future cash flows of the notes (categorized within Level 3 of the fair value hierarchy); the discount rate used approximated the current market rate for loans with similar maturities and credit quality. The fair values of the Company’s fixed-rate notes payable and notes payable to trusts were estimated using the discounted estimated future cash payments to be made on such debt (categorized within Level 3 of the fair value hierarchy); the discount rates used approximated current market rates for loans, or groups of loans, with similar maturities and credit quality. The fair value of the Company’s exchangeable senior notes was estimated using an average market price for similar securities obtained from a third party.
	The fair values of the Company’s fixed-rate assets and liabilities were as follows for the periods indicated:
		March 31, 2015						December 31, 2014
		Fair			Carrying			Fair			Carrying
		Value			Value			Value			Value
	Notes receivable from Preferred Operating Partnership unit holders	$	129,102		$	120,230		$	126,380		$	120,230
	Fixed rate notes payable and notes payable to trusts	$	1,487,014		$	1,438,400		$	1,320,370		$	1,283,893
	Exchangeable senior notes	$	310,625		$	250,000		$	276,095		$	250,000
Earnings Per Common Share	Basic earnings per common share is computed using the two-class method by dividing net income attributable to common stockholders by the weighted average number of common shares outstanding during the period. All outstanding unvested restricted stock awards contain rights to non-forfeitable dividends and participate in undistributed earnings with common stockholders; accordingly, they are considered participating securities that are included in the two-class method. Diluted earnings per common share measures the performance of the Company over the reporting period while giving effect to all potential common shares that were dilutive and outstanding during the period. The denominator includes the weighted average number of basic shares and the number of additional common shares that would have been outstanding if the potential common shares that were dilutive had been issued, and is calculated using either the two-class, treasury stock or as if-converted method, whichever is most dilutive. Potential common shares are securities (such as options, convertible debt, Series A Participating Redeemable Preferred Units (“Series A Units”), Series B Redeemable Preferred Units (“Series B Units”), Series C Convertible Redeemable Preferred Units (“Series C Units”), Series D Redeemable Preferred Units (“Series D Units”) and common Operating Partnership units (“OP Units”)) that do not have a current right to participate in earnings of the Company but could do so in the future by virtue of their option, redemption or conversion right.
	In computing the dilutive effect of convertible securities, net income is adjusted to add back any changes in earnings in the period associated with the convertible security. The numerator also is adjusted for the effects of any other non-discretionary changes in income or loss that would result from the assumed conversion of those potential common shares. In computing diluted earnings per common share, only potential common shares that are dilutive (those that reduce earnings per common share) are included. For the three months ended March 31, 2015 and 2014, options to purchase approximately 19,762 and 18,100 shares of common stock, respectively, were excluded from the computation of earnings per share as their effect would have been anti-dilutive.
	The following table presents the number of Preferred Operating Partnership units, and the potential common shares, that were excluded from the computation of earnings per share as their effect would have been anti-dilutive, assuming full conversion at the average share price for the quarter of $65.59.
		For the Three Months Ended March 31,
		2015						2014
		Number of			Equivalent			Number of			Equivalent
		Units			Shares			Units			Shares
					(if converted)						(if converted)
	Series B Units		1,676,087			638,850			1,342,727			724,232
	Series C Units		704,016			451,884			407,996			370,585
	Series D Units		548,390			209,022			—			—
			2,928,493			1,299,756			1,750,723			1,094,817
	The Operating Partnership had $250,000 of its 2.375% Exchangeable Senior Notes due 2033 (the “Notes”) issued and outstanding as of March 31, 2015. The Notes could potentially have a dilutive impact on the Company’s earnings per share calculations. The Notes are exchangeable by holders into shares of the Company’s common stock under certain circumstances per the terms of the indenture governing the Notes. The exchange price of the Notes was $55.62 per share as of March 31, 2015, and could change over time as described in the indenture. The Company has irrevocably agreed to pay only cash for the accreted principal amount of the Notes relative to its exchange obligations, but retained the right to satisfy the exchange obligation in excess of the accreted principal amount in cash and/or common stock.
	Though the Company has retained that right, Accounting Standards Codification (“ASC”) 260, “Earnings per Share,” requires an assumption that shares would be used to pay the exchange obligation in excess of the accreted principal amount, and requires that those shares be included in the Company’s calculation of weighted average common shares outstanding for the diluted earnings per share computation. For the three months ended March 31, 2015, 682,502 shares related to the Notes were included in the computation for diluted earnings per share. For the three months ended March 31, 2014, no shares related to the Notes were included in the computation for diluted earnings per share as the exchange price exceeded the per share price of the Company’s common stock during this period.
	For the purposes of computing the diluted impact on earnings per share of the potential exchange of Series A Units for common shares upon redemption, where the Company has the option to redeem in cash or shares and where the Company has stated the positive intent and ability to settle at least $115,000 of the instrument in cash (or net settle a portion of the Series A Units against the related outstanding note receivable), only the amount of the instrument in excess of $115,000 is considered in the calculation of shares contingently issuable for the purposes of computing diluted earnings per share as allowed by ASC 260-10-45-46.
	For the purposes of computing the diluted impact on earnings per share of the potential exchange of Series B Units for common shares upon redemption, where the Company has the option to redeem in cash or shares and where the Company has stated the intent and ability to settle the redemption in shares, the Company divided the total value of the Series B Units outstanding as of March 31, 2015 of $41,902 by the closing price of the Company’s common stock as of March 31, 2015 of $67.57 per share. Assuming full exchange for common shares as of March 31, 2015, 620,127 shares would have been issued to the holders of the Series B Units.
	For the purposes of computing the diluted impact on earnings per share of the potential exchange of Series C Units for common shares upon redemption, where the Company has the option to redeem in cash or shares and where the Company has stated the intent and ability to settle the redemption in shares, the Company divided the total value of the Series C Units outstanding as of March 31, 2015 of $29,639 by the closing price of the Company’s common stock as of March 31, 2015 of $67.57 per share. Assuming full exchange for common shares as of March 31, 2015, 438,641 shares would have been issued to the holders of the Series C Units.
	For the purposes of computing the diluted impact on earnings per share of the potential exchange of Series D Units for common shares upon redemption, where the Company has the option to redeem in cash or shares and where the Company has stated the intent and ability to settle the redemption in shares, the Company divided the total value of the Series D Units outstanding as of March 31, 2015 of $13,710 by the closing price of the Company’s common stock as of March 31, 2015 of $67.57 per share. Assuming full exchange for common shares as of March 31, 2015, 202,901 shares would have been issued to the holders of Series D Units.
	The computation of earnings per common share was as follows for the periods presented:
		For the Three Months Ended
		March 31,
		2015			2014
	Net income attributable to common stockholders	$	53,742		$	37,340
	Earnings and dividends allocated to participating securities		(119	)		(117	)
	Earnings for basic computations		53,623			37,223
	Earnings and dividends allocated to participating securities		119			—
	Income allocated to noncontrolling interest—Preferred Operating Partnership (Series A Units) and Operating Partnership		3,635			3,128
	Fixed component of income allocated to noncontrolling interest—Preferred Operating Partnership (Series A Units)		(1,274	)		(1,438	)
	Net income for diluted computations	$	56,103		$	38,913
	Weighted average common shares outstanding:
	Average number of common shares outstanding—basic		116,117,615			115,438,325
	Series A Units		875,480			989,980
	OP Units		4,365,879			4,334,118
	Unvested restricted stock awards included for treasury stock method		282,903			—
	Shares related to exchangeable senior notes and dilutive stock options		953,841			300,422
	Average number of common shares outstanding—diluted		122,595,718			121,062,845
	Earnings per common share
	Basic	$	0.46		$	0.32
	Diluted	$	0.46		$	0.32
Derivatives	DERIVATIVES
	The Company is exposed to certain risks arising from both its business operations and economic conditions. The Company principally manages its exposures to a wide variety of business and operational risks through management of its core business activities. The Company manages economic risks, including interest rate, liquidity and credit risk, primarily by managing the amount, sources and duration of its debt funding and by using derivative financial instruments. Specifically, the Company enters into derivative financial instruments to manage exposure that arises from business activities that result in the receipt or payment of future known and uncertain cash amounts, the value of which are determined by interest rates. The Company’s derivative financial instruments are used to manage differences in the amount, timing and duration of the Company’s known or expected cash receipts and its known or expected cash payments principally related to the Company’s investments and borrowings.
Convertible Debt	GAAP requires entities with convertible debt instruments that may be settled entirely or partially in cash upon conversion to separately account for the liability and equity components of the instrument in a manner that reflects the issuer’s economic interest cost. The Company therefore accounts for the liability and equity components of the Notes separately. The equity component is included in additional paid-in capital in stockholders’ equity in the condensed consolidated balance sheets, and the value of the equity component is treated as original issue discount for purposes of accounting for the debt component. The discount is being amortized as interest expense over the remaining period of the debt through its first redemption date, July 1, 2018. The effective interest rate on the liability component is 4.0%.

Fair_Value_Disclosures_Tables

Fair Value Disclosures (Tables)	3 Months Ended
	Mar. 31, 2015
Fair Value Disclosures [Abstract]
Schedule of Assets and Liabilities Measured at Fair Value on a Recurring Basis	The table below presents the Company’s assets and liabilities measured at fair value on a recurring basis as of March 31, 2015, aggregated by the level in the fair value hierarchy within which those measurements fall.
		March 31,			Fair Value Measurements at Reporting Date Using
	Description	2015			Quoted Prices in		Significant Other			Significant
					Active Markets		Observable			Unobservable
					for Identical		Inputs (Level 2)			Inputs (Level 3)
					Assets (Level 1)
	Other assets—Cash Flow Hedge Swap Agreements	$	688		$	—	$	688		$	—
	Other liabilities—Cash Flow Hedge Swap Agreements	$	(7,231	)	$	—	$	(7,231	)	$	—
Schedule of Fair Value of Financial Instruments	The fair values of the Company’s fixed-rate assets and liabilities were as follows for the periods indicated:
		March 31, 2015					December 31, 2014
		Fair			Carrying		Fair			Carrying
		Value			Value		Value			Value
	Notes receivable from Preferred Operating Partnership unit holders	$	129,102		$	120,230	$	126,380		$	120,230
	Fixed rate notes payable and notes payable to trusts	$	1,487,014		$	1,438,400	$	1,320,370		$	1,283,893
	Exchangeable senior notes	$	310,625		$	250,000	$	276,095		$	250,000

Earnings_Per_Common_Share_Tabl

Earnings Per Common Share (Tables)	3 Months Ended
	Mar. 31, 2015
Earnings Per Share [Abstract]
Schedule of Antidilutive Shares Excluded from Computation of Earnings Per Share	The following table presents the number of Preferred Operating Partnership units, and the potential common shares, that were excluded from the computation of earnings per share as their effect would have been anti-dilutive, assuming full conversion at the average share price for the quarter of $65.59.
		For the Three Months Ended March 31,
		2015						2014
		Number of			Equivalent			Number of		Equivalent
		Units			Shares			Units		Shares
					(if converted)					(if converted)
	Series B Units		1,676,087			638,850			1,342,727		724,232
	Series C Units		704,016			451,884			407,996		370,585
	Series D Units		548,390			209,022			—		—
			2,928,493			1,299,756			1,750,723		1,094,817
Schedule of Computation of Earnings Per Common Share	The computation of earnings per common share was as follows for the periods presented:
		For the Three Months Ended
		March 31,
		2015			2014
	Net income attributable to common stockholders	$	53,742		$	37,340
	Earnings and dividends allocated to participating securities		(119	)		(117	)
	Earnings for basic computations		53,623			37,223
	Earnings and dividends allocated to participating securities		119			—
	Income allocated to noncontrolling interest—Preferred Operating Partnership (Series A Units) and Operating Partnership		3,635			3,128
	Fixed component of income allocated to noncontrolling interest—Preferred Operating Partnership (Series A Units)		(1,274	)		(1,438	)
	Net income for diluted computations	$	56,103		$	38,913
	Weighted average common shares outstanding:
	Average number of common shares outstanding—basic		116,117,615			115,438,325
	Series A Units		875,480			989,980
	OP Units		4,365,879			4,334,118
	Unvested restricted stock awards included for treasury stock method		282,903			—
	Shares related to exchangeable senior notes and dilutive stock options		953,841			300,422
	Average number of common shares outstanding—diluted		122,595,718			121,062,845
	Earnings per common share
	Basic	$	0.46		$	0.32
	Diluted	$	0.46		$	0.32

Store_Acquisitions_Tables

Store Acquisitions (Tables)	3 Months Ended
	Mar. 31, 2015
Business Combinations [Abstract]
Schedule of Operating Properties Acquired	The following table summarizes the Company’s acquisitions of operating stores for the three months ended March 31, 2015, and does not include purchases of raw land or improvements made to existing assets:
			Number		Date of		Consideration Paid														Acquisition Date Fair Value
			of		Acquisition
	Property Location		Stores				Total		Cash		Non-cash		Notes		Previous			Net			Land		Building		Intangible		Closing costs—
									Paid		gain		Receivable		equity			Liabilities/(Assets)									expensed (1)
															interest			Assumed
	California (2)			1		3/30/15	$	12,699	$	1,700	$	1,629	$	11,009	$	(1,264	)	$	(375	)	$	1,025	$	11,479	$	195	$	—
	North Carolina, South Carolina			2		3/30/15		13,165		13,143		—		—		—			22			1,763		11,229		144		29
	Virginia			1		3/17/15		5,073		5,065		—		—		—			8			118		4,797		81		77
	Texas			1		2/24/15		13,570		13,519		—		—		—			51			1,511		11,861		182		16
	Texas			3		1/13/15		41,904		41,806		—		—		—			98			12,080		29,489		300		35
	2015 Totals			8			$	86,411	$	75,233	$	1,629	$	11,009	$	(1,264	)	$	(196	)	$	16,497	$	68,855	$	902	$	157
	-1	This column represents costs paid at closing. The amounts shown exclude other acquisition costs paid before or after the closing date.
	-2	This represents the acquisition of a joint venture partners’ interest in Extra Space of Sacramento One LLC (“Sacramento One”), an existing joint venture, for $1,700 in cash. The result of the acquisition is that the Company owns 100% of Sacramento One, which owned one store located in California. Prior to the acquisition date, the Company accounted for its interest in Sacramento One as an equity-method investment, and the Company also held mortgage notes receivable from Sacramento One totalling $11,009, including related interest. The total acquisition date fair value of the Company’s previous equity interest was approximately $365 and is included in consideration transfered. The Company recognized a non-cash gain of $1,629 as a result of remeasuring the fair value of its equity interest held prior to the acquisition. The store is consolidated subsequent to the acquisition as the Company owns 100% of the store.

Variable_Interests_Tables

Variable Interests (Tables)	3 Months Ended
	Mar. 31, 2015
Equity Method Investments and Joint Ventures [Abstract]
Schedule of Liabilities and Maximum Exposure to Loss Related to Trusts	Following is a tabular comparison of the liabilities the Company has recorded as a result of its involvement with the Trusts to the maximum exposure to loss the Company is subject to as a result of such involvement as of March 31, 2015:
		Notes		Investment		Maximum		Difference
		payable		Balance		exposure
		to Trusts				to loss
	Trust	$	36,083	$	1,083	$	35,000	$	—
	Trust II		42,269		1,269		41,000		—
	Trust III		41,238		1,238		40,000		—
		$	119,590	$	3,590	$	116,000	$	—

Derivatives_Tables

Derivatives (Tables)	3 Months Ended
	Mar. 31, 2015
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Schedule of Balance Sheet Classification and Fair Value of Entity's Derivative Financial Instruments	The table below presents the fair value of the Company’s derivative financial instruments as well as their classification on the condensed consolidated balance sheets:
		Asset (Liability) Derivatives
		March 31,				December 31,
		2015				2014
	Derivatives designated as hedging instruments:
	Other assets	$	688			$	3,583
	Other liabilities	$	(7,231	)		$	(3,533	)
Interest Payments Recognized as an Increase or Decrease in Interest Expense	The tables below present the effect of the Company’s derivative financial instruments on the condensed consolidated statements of operations for the periods presented. No tax effect has been presented as the derivative instruments are held by the Company:
		Classification of		For the Three Months
		Income (Expense)		Ended March 31,
	Type			2015				2014
	Swap Agreements	Interest expense		$	(2,297	)		$	(2,293	)
Schedule of Information Relating to Gain (Loss) Recognized on Swap Agreements		Gain (loss)								Location of	Gain (loss)
		recognized in OCI								amounts	reclassifed from
		March 31,								reclassified from	OCI
										OCI into income	For the Three
											Months Ended
											March 31,
	Type	2015				2014					2015			2014
	Swap Agreements	$	(8,875	)		$	(5,043	)		Interest expense	$	(2,297	)	$	(2,293	)

Exchangeable_Senior_Notes_Tabl

Exchangeable Senior Notes (Tables)	3 Months Ended
	Mar. 31, 2015
Text Block [Abstract]
Schedule of Information about Carrying Amount of Equity Component, Principal Amount of Liability Component, Unamortized Discount and Net Carrying Amount for Notes	Information about the carrying amount of the equity component, the principal amount of the liability component, its unamortized discount and its net carrying amount was as follows for the periods indicated:
		March 31,			December 31,
		2015			2014
	Carrying amount of equity component	$	14,496		$	14,496
	Principal amount of liability component	$	250,000		$	250,000
	Unamortized discount—equity component		(9,751	)		(10,448	)
	Unamortized cash discount		(2,418	)		(2,606	)
	Net carrying amount of liability component	$	237,831		$	236,946
Summary of Amount of Interest Cost Recognized Relating to Contractual Interest Rate and Amortization of Discount on Liability Component of Notes	The amount of interest cost recognized relating to the contractual interest rate and the amortization of the discount on the liability component of the Notes were as follows for the periods indicated:
		For the Three
		Months Ended
		March 31,
		2015			2014
	Contractual interest	$	1,484		$	1,484
	Amortization of discount		697			662
	Total interest expense recognized	$	2,181		$	2,146

Segment_Information_Tables

Segment Information (Tables)	3 Months Ended
	Mar. 31, 2015
Segment Reporting [Abstract]
Schedule of Financial Information of Business Segments	Financial information for the Company’s business segments is presented below:
		March 31,			December 31,
		2015			2014
	Balance Sheet
	Investment in unconsolidated real estate ventures
	Rental operations	$	85,602		$	85,711
	Total assets
	Rental operations	$	4,194,744		$	4,109,673
	Tenant reinsurance		38,745			39,383
	Property management, acquisition and development		230,656			253,051
		$	4,464,145		$	4,402,107
		For the Three Months
		Ended March 31,
		2015			2014
	Statement of Operations
	Total revenues
	Rental operations	$	148,894		$	132,001
	Tenant reinsurance		16,510			13,463
	Property management, acquisition and development		7,750			7,123
			173,154			152,587
	Operating expenses, including depreciation and amortization
	Rental operations		75,509			69,942
	Tenant reinsurance		2,928			2,567
	Property management, acquisition and development		19,281			19,680
			97,718			92,189
	Income (loss) from operations
	Rental operations		73,385			62,059
	Tenant reinsurance		13,582			10,896
	Property management, acquisition and development		(11,531	)		(12,557	)
			75,436			60,398
	Interest expense
	Rental operations		(21,830	)		(19,310	)
	Property management, acquisition and development		399			(288	)
			(21,431	)		(19,598	)
	Non-cash interest expense related to the amortization of discount on equity component of exchangeable senior notes
	Property management, acquisition and development		(697	)		(662	)
	Interest income
	Tenant reinsurance		4			4
	Property management, acquisition and development		852			265
			856			269
	Interest income on note receivable from Preferred Operating Partnership unit holder
	Property management, acquisition and development		1,213			1,213
	Equity in earnings of unconsolidated real estate ventures
	Rental operations		2,650			2,419
	Equity in earnings of unconsolidated real estate ventures—gain on sale of real estate assets and purchase of partners’ interests
	Rental operations		2,857			—
	Income tax expense
	Rental operations		(754	)		(434	)
	Tenant reinsurance		(1,874	)		(3,815	)
	Property management, acquisition and development		380			1,419
			(2,248	)		(2,830	)
	Net income (loss)
	Rental operations		56,308			44,734
	Tenant reinsurance		11,712			7,085
	Property management, acquisition and development		(9,384	)		(10,610	)
		$	58,636		$	41,209
	Depreciation and amortization expense
	Rental operations	$	28,265		$	26,460
	Property management, acquisition and development		2,163			1,915
		$	30,428		$	28,375
	Statement of Cash Flows
	Acquisition of real estate assets
	Property management, acquisition and development	$	(77,082	)	$	(253,939	)
	Development and redevelopment of real estate assets
Property management, acquisition and development	$	(3,140	)	$	(2,820	)

Organization_Additional_Inform

Organization - Additional Information (Detail)	3 Months Ended
	Mar. 31, 2015
	Segments
	Store
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Number of operating storage facilities in which the entity has equity interests (in stores)	835
Number of stores owned by franchisees and third parties	271
Number of operating stores owned and/or managed	1,106
Number of states in which operating storage facilities are located	35
Number of reportable segments	3
Rental Revenue [Member] | Customer Concentration Risk [Member]
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Maximum percentage of rental income accounted for by any single tenant	5.00%

Fair_Value_Disclosures_Schedul

Fair Value Disclosures - Schedule of Assets and Liabilities Measured at Fair Value on a Recurring Basis (Detail) (Recurring Basis [Member], USD $)	Mar. 31, 2015
In Thousands, unless otherwise specified
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets-Cash Flow Hedge Swap Agreements	$688
Other liabilities-Cash Flow Hedge Swap Agreements	-7,231
Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets-Cash Flow Hedge Swap Agreements	688
Other liabilities-Cash Flow Hedge Swap Agreements	($7,231)

Fair_Value_Disclosures_Additio

Fair Value Disclosures - Additional Information (Detail) (USD $)	Mar. 31, 2015
Fair Value Disclosures [Abstract]
Transfer of assets between level 1 and level 2	$0
Transfer of assets between level 2 and level 1	0
Transfer of liabilities between level 1 and level 2	0
Transfer of liabilities between level 2 and level 1	$0

Fair_Value_Disclosures_Schedul1

Fair Value Disclosures - Schedule of Fair Value of Financial Instruments (Detail) (USD $)	Mar. 31, 2015	Dec. 31, 2014
In Thousands, unless otherwise specified
Fair Value of Financial Instruments [Line Items]
Notes receivable from Preferred Operating Partnership unit holders	$120,230	$120,230
Exchangeable senior notes	250,000	250,000
Carrying Value [Member]
Fair Value of Financial Instruments [Line Items]
Notes receivable from Preferred Operating Partnership unit holders	120,230	120,230
Fixed rate notes payable and notes payable to trusts	1,438,400	1,283,893
Exchangeable senior notes	250,000	250,000
Fair Value [Member]
Fair Value of Financial Instruments [Line Items]
Notes receivable from Preferred Operating Partnership unit holders	129,102	126,380
Fixed rate notes payable and notes payable to trusts	1,487,014	1,320,370
Exchangeable senior notes	$310,625	$276,095

Earnings_Per_Common_Share_Sche

Earnings Per Common Share - Schedule of Antidilutive Shares Excluded from Computation of Earnings Per Share (Detail)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Number of Units	2,928,493	1,750,723
Equivalent Shares (if converted)	1,299,756	1,094,817
Series B Units [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Number of Units	1,676,087	1,342,727
Equivalent Shares (if converted)	638,850	724,232
Series C Units [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Number of Units	704,016	407,996
Equivalent Shares (if converted)	451,884	370,585
Series D Units [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Number of Units	548,390
Equivalent Shares (if converted)	209,022

Earnings_Per_Common_Share_Addi

Earnings Per Common Share - Additional Information (Detail) (USD $)	3 Months Ended
In Thousands, except Share data, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014	Jun. 21, 2013
Earnings Per Common Share [Line Items]
Average share price	$65.59
Average closing price of common stock	$67.57
Anti-dilutive securities excluded from computation of earnings per common share	875,480	989,980
Series A Units [Member]
Earnings Per Common Share [Line Items]
Exchangeable preferred operating partnership units settled in cash, minimum	$115,000
Series B Units [Member]
Earnings Per Common Share [Line Items]
Units outstanding	41,902
Anti-dilutive securities excluded from computation of earnings per common share	620,127
Series C Units [Member]
Earnings Per Common Share [Line Items]
Units outstanding	29,639
Anti-dilutive securities excluded from computation of earnings per common share	438,641
Series D Units [Member]
Earnings Per Common Share [Line Items]
Units outstanding	13,710
Anti-dilutive securities excluded from computation of earnings per common share	202,901
Operating Partnership [Member] | 2.375% Exchangeable Senior Notes [Member]
Earnings Per Common Share [Line Items]
Principal amount of notes issued	$250,000		$250,000
Interest rate	2.38%		2.38%
Exchange price	$55.62
Shares related to the Notes were included in the computation for diluted earnings per share	682,502	0
Stock Options [Member]
Earnings Per Common Share [Line Items]
Anti-dilutive securities excluded from computation of earnings per common share	19,762	18,100

Earnings_Per_Common_Share_Sche1

Earnings Per Common Share - Schedule of Computation of Earnings Per Common Share (Detail) (USD $)	3 Months Ended
In Thousands, except Share data, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Earnings Per Share [Abstract]
Net income attributable to common stockholders	$53,742	$37,340
Earnings and dividends allocated to participating securities	-119	-117
Earnings for basic computations	53,623	37,223
Earnings and dividends allocated to participating securities	119
Income allocated to noncontrolling interest-Preferred Operating Partnership (Series A Units) and Operating Partnership	3,635	3,128
Fixed component of income allocated to noncontrolling interest-Preferred Operating Partnership (Series A Units)	-1,274	-1,438
Net income for diluted computations	$56,103	$38,913
Weighted average common shares outstanding:
Average number of common shares outstanding-basic	116,117,615	115,438,325
Series A Units	875,480	989,980
OP Units	4,365,879	4,334,118
Unvested restricted stock awards included for treasury stock method	282,903
Shares related to exchangeable senior notes and dilutive stock options	953,841	300,422
Average number of common shares outstanding-diluted	122,595,718	121,062,845
Earnings per common share
Basic	$0.46	$0.32
Diluted	$0.46	$0.32

Store_Acquisitions_Schedule_of

Store Acquisitions - Schedule of Operating Properties Acquired (Detail) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015
	Property
Property Acquisitions [Line Items]
Number of Stores	8
Total Consideration Paid	$86,411
Cash Consideration Paid	75,233
Non-cash gain	1,629
Notes Receivable	11,009
Previous equity interest	-1,264
Net Liabilities/(Assets) Assumed	-196
Acquisition Date Fair Value, Land	16,497
Acquisition Date Fair Value, Building	68,855
Acquisition Date Fair Value, Intangible	902
Closing costs-expensed	157
California 1 Property 3/30/2015 [Member ]
Property Acquisitions [Line Items]
Number of Stores	1
Total Consideration Paid	12,699
Cash Consideration Paid	1,700
Non-cash gain	1,629
Notes Receivable	11,009
Previous equity interest	-1,264
Net Liabilities/(Assets) Assumed	-375
Acquisition Date Fair Value, Land	1,025
Acquisition Date Fair Value, Building	11,479
Acquisition Date Fair Value, Intangible	195
North Carolina South Carolina 2 Property 3/30/2015 [Member]
Property Acquisitions [Line Items]
Number of Stores	2
Total Consideration Paid	13,165
Cash Consideration Paid	13,143
Net Liabilities/(Assets) Assumed	22
Acquisition Date Fair Value, Land	1,763
Acquisition Date Fair Value, Building	11,229
Acquisition Date Fair Value, Intangible	144
Closing costs-expensed	29
Virginia 1 Property 3/17/2015 [Member]
Property Acquisitions [Line Items]
Number of Stores	1
Total Consideration Paid	5,073
Cash Consideration Paid	5,065
Net Liabilities/(Assets) Assumed	8
Acquisition Date Fair Value, Land	118
Acquisition Date Fair Value, Building	4,797
Acquisition Date Fair Value, Intangible	81
Closing costs-expensed	77
Texas 1 Property 2/24/2015 [Member]
Property Acquisitions [Line Items]
Number of Stores	1
Total Consideration Paid	13,570
Cash Consideration Paid	13,519
Net Liabilities/(Assets) Assumed	51
Acquisition Date Fair Value, Land	1,511
Acquisition Date Fair Value, Building	11,861
Acquisition Date Fair Value, Intangible	182
Closing costs-expensed	16
Texas 3 Property January 13, 2015 [Member]
Property Acquisitions [Line Items]
Number of Stores	3
Total Consideration Paid	41,904
Cash Consideration Paid	41,806
Net Liabilities/(Assets) Assumed	98
Acquisition Date Fair Value, Land	12,080
Acquisition Date Fair Value, Building	29,489
Acquisition Date Fair Value, Intangible	300
Closing costs-expensed	$35

Store_Acquisitions_Schedule_of1

Store Acquisitions - Schedule of Operating Properties Acquired (Parenthetical) (Detail) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015
	Store
Property Acquisitions [Line Items]
Number of operating stores owned by consolidated joint venture	19
Non-cash gain	$1,629
Company held mortgage notes receivable eliminated as a result of the acquisition	11,009
Extra Space of Sacramento One LLC [Member]
Property Acquisitions [Line Items]
Cash portion of payment for acquisition	1,700
Equity Ownership (as a percent)	100.00%
Number of operating stores owned by consolidated joint venture	1
Previous equity interest, fair value	365
Non-cash gain	1,629
Company held mortgage notes receivable eliminated as a result of the acquisition	$11,009

Variable_Interests_Additional_

Variable Interests - Additional Information (Detail)	Mar. 31, 2015
	JointVenture
	Item
Variable Interests And Equity Method Investments Disclosure [Abstract]
Number of wholly-owned unconsolidated subsidiaries	3
Number of interests in consolidated VIE joint ventures	0

Variable_Interests_Schedule_of

Variable Interests - Schedule of Liabilities and Maximum Exposure to Loss Related to Trusts (Detail) (USD $)	Mar. 31, 2015	Dec. 31, 2014
In Thousands, unless otherwise specified
Variable Interest Entity [Line Items]
Notes payable to Trusts	$119,590	$119,590
Operating Partnership [Member] | Variable Interest Entity, Not Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Notes payable to Trusts	119,590
Investment Balance	3,590
Maximum exposure to loss	116,000
Difference	0
Operating Partnership [Member] | Variable Interest Entity, Not Primary Beneficiary [Member] | Trust I [Member]
Variable Interest Entity [Line Items]
Notes payable to Trusts	36,083
Investment Balance	1,083
Maximum exposure to loss	35,000
Difference	0
Operating Partnership [Member] | Variable Interest Entity, Not Primary Beneficiary [Member] | Trust II [Member]
Variable Interest Entity [Line Items]
Notes payable to Trusts	42,269
Investment Balance	1,269
Maximum exposure to loss	41,000
Difference	0
Operating Partnership [Member] | Variable Interest Entity, Not Primary Beneficiary [Member] | Trust III [Member]
Variable Interest Entity [Line Items]
Notes payable to Trusts	41,238
Investment Balance	1,238
Maximum exposure to loss	40,000
Difference	$0

Derivatives_Additional_Informa

Derivatives - Additional Information (Detail) (USD $)	Mar. 31, 2015
In Thousands, unless otherwise specified	Item
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Number of derivative financial instruments	23
Combined notional amount	$825,987
Estimated termination value on settlement	$7,740

Derivatives_Schedule_of_Balanc

Derivatives - Schedule of Balance Sheet Classification and Fair Value of Entity's Derivative Financial Instruments (Detail) (USD $)	Mar. 31, 2015	Dec. 31, 2014
In Thousands, unless otherwise specified
Other Assets [Member]
Derivative [Line Items]
Other assets - Asset (Liability) Derivatives	$688	$3,583
Other Liabilities [Member]
Derivative [Line Items]
Other liabilities - Asset (Liability) Derivatives	($7,231)	($3,533)

Derivatives_Interest_Payments_

Derivatives - Interest Payments Recognized as Increase or Decrease in Interest Expense (Detail) (Interest Rate Swap [Member], USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Interest Rate Swap [Member]
Derivative [Line Items]
Swap agreements increase (decrease) in interest expenses due to interest payments	($2,297)	($2,293)

Derivatives_Schedule_of_Inform

Derivatives - Schedule of Information Relating to Gain (Loss) Recognized on Swap Agreements (Detail) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Swap agreements gain (loss) recognized in OCI	($8,875)	($5,043)
Swap agreements gain (loss) reclassified from OCI - Interest expense	($2,297)	($2,293)

Exchangeable_Senior_Notes_Addi

Exchangeable Senior Notes - Additional Information (Detail) (USD $)	0 Months Ended	3 Months Ended
In Thousands, unless otherwise specified	Jun. 21, 2013	Mar. 31, 2015	Dec. 31, 2014	Jun. 21, 2013
Debt Instrument [Line Items]
Unamortized cash discount		$12,169	$13,054
Effective interest rate on the liability component		4.00%
2.375% Exchangeable Senior Notes [Member] | Operating Partnership [Member]
Debt Instrument [Line Items]
Principal amount of notes issued	250,000	250,000		250,000
Interest rate	2.38%	2.38%		2.38%
Discount rate (as a percent)	1.50%			1.50%
Issuance cost	1,672
Amortization period	5 years
Conversion ratio, number of shares per $1,000 principal amount, numerator		17.98
Principal amount used for debt instrument conversion ratio		1,000
Unamortized cash discount	$3,750	$2,418	$2,606	$3,750
Redemption price as percentage of principal amount of notes plus accrued and unpaid interest	100.00%
Redemption price as percentage of principal amount of notes at request of debt holders and upon occurrence of designated event	100.00%
Minimum [Member] | 2.375% Exchangeable Senior Notes [Member] | Operating Partnership [Member]
Debt Instrument [Line Items]
Number of days of written notice to holders of notes required for redemption	30 days
Maximum [Member] | 2.375% Exchangeable Senior Notes [Member] | Operating Partnership [Member]
Debt Instrument [Line Items]
Number of days of written notice to holders of notes required for redemption	60 days

Exchangeable_Senior_Notes_Sche

Exchangeable Senior Notes - Schedule of Information about Carrying Amount of Equity Component, Principal Amount of Liability Component, Unamortized Discount and Net Carrying Amount for Notes (Detail) (USD $)	Mar. 31, 2015	Dec. 31, 2014	Jun. 21, 2013
In Thousands, unless otherwise specified
Debt Instrument [Line Items]
Principal amount of liability component	$250,000	$250,000
Unamortized cash discount	-12,169	-13,054
Operating Partnership [Member] | 2.375% Exchangeable Senior Notes [Member]
Debt Instrument [Line Items]
Carrying amount of equity component	14,496	14,496
Principal amount of liability component	250,000	250,000
Unamortized discount-equity component	-9,751	-10,448
Unamortized cash discount	-2,418	-2,606	-3,750
Net carrying amount of liability component	$237,831	$236,946

Exchangeable_Senior_Notes_Summ

Exchangeable Senior Notes - Summary of Amount of Interest Cost Recognized Relating to Contractual Interest Rate and Amortization of Discount on Liability Component of Notes (Detail) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Debt Instrument [Line Items]
Amortization of discount	$697	$662
2033 Notes [Member]
Debt Instrument [Line Items]
Contractual interest	1,484	1,484
Amortization of discount	697	662
Total interest expense recognized	$2,181	$2,146

Noncontrolling_Interest_Repres

Noncontrolling Interest Represented by Preferred Operating Partnership Units - Series A Participating Redeemable Preferred Units - Additional Information (Detail) (USD $)	0 Months Ended	3 Months Ended	0 Months Ended
In Thousands, except Share data, unless otherwise specified	Jun. 15, 2007	Mar. 31, 2015	Oct. 03, 2014	Jun. 25, 2007	Dec. 31, 2014
	Property		Share_for_Share
Noncontrolling Interest in Operating Partnership [Line Items]
Loan to holders of preferred OP units		$120,230			$120,230
Operating Partnership [Member] | Series A Participating Redeemable Preferred Units [Member]
Noncontrolling Interest in Operating Partnership [Line Items]
Number of stores acquired	10
Operating Partnership [Member] | Series A Participating Redeemable Preferred Units [Member] | Series A Units [Member]
Noncontrolling Interest in Operating Partnership [Line Items]
Preferred units issued as part of acquisition	989,980
Fixed priority return on preferred OP units, stated return rate (as a percent)		5.00%
Fixed priority return on preferred OP units, amount		115,000
Fixed priority return on preferred OP units, liquidation value		115,000
Operating Partnership Holders of A Units [Member] | Series A Participating Redeemable Preferred Units [Member]
Noncontrolling Interest in Operating Partnership [Line Items]
Loan to holders of preferred OP units				100,000
Note receivable interest rate (as a percent)				4.85%
Maximum number of preferred OP units converted prior to the maturity date of the loan (in shares)				114,500
A units redeemed			114,500
A units redeemed ,value			4,794
Additional units redeemed			0
Common stock shares redeemed			280,331
Preferred OP units, current liquidation value			$101,699

Noncontrolling_Interest_Repres1

Noncontrolling Interest Represented by Preferred Operating Partnership Units - Series B Redeemable Preferred Units - Additional Information (Detail) (Series B Redeemable Preferred Units [Member], USD $)	3 Months Ended	0 Months Ended
In Thousands, except Share data, unless otherwise specified	Mar. 31, 2015	Apr. 03, 2014	Sep. 26, 2013	Aug. 29, 2013
			Store	Store
Series B Units [Member]
Noncontrolling Interest in Operating Partnership [Line Items]
Liquidation value (in dollars per share)	$25
Fixed liquidation value	$41,902
Annual rate of return (as a percent)	6.00%
Georgia, 1 Property Acquired 4/3/2014 [Member] | Series B Units [Member]
Noncontrolling Interest in Operating Partnership [Line Items]
Preferred OP units issued as part of the acquisition (in shares)		333,360
Preferred OP units issued as part of the acquisition		8,334
Georgia, 1 Property Acquired 4/3/2014 [Member] | Operating Partnership [Member]
Noncontrolling Interest in Operating Partnership [Line Items]
Cash portion of payment for acquisition		15,158
Number of stores acquired		1
California, 20 Properties Acquired 2013-September [Member] | Operating Partnership [Member]
Noncontrolling Interest in Operating Partnership [Line Items]
Cash portion of payment for acquisition			100,876
Number of stores acquired			1	19
Number of stores acquired as part of portfolio acquisition				20
Debt assumed			98,960
Number of common units issued as part of acquisition			1,448,108
OP units issued as part of the acquisition			62,341
California, 20 Properties Acquired 2013-September [Member] | Operating Partnership [Member] | Series B Units [Member]
Noncontrolling Interest in Operating Partnership [Line Items]
Preferred OP units issued as part of the acquisition (in shares)			1,342,727
Preferred OP units issued as part of the acquisition			$33,568

Noncontrolling_Interest_Repres2

Noncontrolling Interest Represented by Preferred Operating Partnership Units - Series C Convertible Redeemable Preferred Units - Additional Information (Detail) (USD $)	0 Months Ended	3 Months Ended	0 Months Ended	6 Months Ended
In Thousands, except Share data, unless otherwise specified	Dec. 31, 2014	Mar. 31, 2015	Nov. 19, 2013	31-May-14
		OperatingPartnershipUnits	Store	Store
Noncontrolling Interest in Operating Partnership [Line Items]
Loan to holders of preferred OP units	$120,230	$120,230
Series C Convertible Redeemable Preferred Units [Member] | Series C Units [Member]
Noncontrolling Interest in Operating Partnership [Line Items]
Liquidation value (in dollars per share)		$42.10
Fixed liquidation value		29,639
Quarterly distribution per preferred OP unit payable above quarterly distribution for common OP Unit		$0.18
Number of quarters immediately preceding the fifth anniversary of issuance for which distribution is payable		12 months
Period from date of issuance after which preferred OP units will become redeemable at the option of the holder		1 year
Period from date of issuance after which preferred OP units will become convertible into common OP units at the option of the holder		1 year
Preferred OP units conversion ratio		0.9145
Loan to holders of preferred OP units	20,230
Note receivable interest rate (as a percent)	5.00%
Note receivable maturity date	15-Dec-24
California, Properties Acquired December 2013 [Member] | Series C Convertible Redeemable Preferred Units [Member]
Noncontrolling Interest in Operating Partnership [Line Items]
Number of self storage facilities acquired			12
Ownership interest in five stores through joint ventures prior to the acquisition				35.00%
Ownership interest in one store through joint ventures prior to the acquisition				40.00%
Number of stores in which ownership interest was held prior to acquisition				1
Number of stores in which ownership interest was held prior to acquisition of remaining properties				5
California, Properties Acquired December 2013 [Member] | Series C Convertible Redeemable Preferred Units [Member] | Operating Partnership [Member]
Noncontrolling Interest in Operating Partnership [Line Items]
Number of stores acquired				6
Cash portion of payment for acquisition				45,722
Debt assumed				37,532
California, Properties Acquired December 2013 [Member] | Series C Convertible Redeemable Preferred Units [Member] | Series C Units [Member] | Operating Partnership [Member]
Noncontrolling Interest in Operating Partnership [Line Items]
Preferred Units Issued as Part of Acquisition (in shares)				704,016
Preferred OP units issued as part of the acquisition				$30,960

Noncontrolling_Interest_Repres3

Noncontrolling Interest Represented by Preferred Operating Partnership Units - Series D Redeemable Preferred Units - Additional Information (Detail) (Series D Redeemable Preferred Units [Member], USD $)	3 Months Ended	0 Months Ended
In Thousands, except Share data, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Series D Units [Member]
Noncontrolling Interest in Operating Partnership [Line Items]
Liquidation value (in dollars per share)	$25
Fixed liquidation value	$13,710
Annual rate of return (as a percent)	5.00%
Self Storage Facility in Florida [Member]
Noncontrolling Interest in Operating Partnership [Line Items]
Cash portion of payment for acquisition		5,621
Self Storage Facility in Florida [Member] | Series D Units [Member]
Noncontrolling Interest in Operating Partnership [Line Items]
Preferred Units Issued as Part of Acquisition (in shares)		548,390
Total consideration paid		$13,710

Noncontrolling_Interest_in_Ope

Noncontrolling Interest in Operating Partnership - Additional Information (Detail) (USD $)	3 Months Ended
In Thousands, except Share data, unless otherwise specified	Mar. 31, 2015
Noncontrolling Interest in Operating Partnership [Line Items]
Period used as a denomination to determine the average closing price of common stock	10 days
OP units conversion basis	One-for-one basis
Ten day average closing stock price	$67.76
Consideration to be paid on redemption of common OP units	$295,832
Operating Partnership [Member]
Noncontrolling Interest in Operating Partnership [Line Items]
Ownership interest held by entity (as a percent)	93.40%
Noncontrolling interest in operating partnership (as a percent)	6.60%
OP units outstanding	4,365,879

Other_Noncontrolling_Interests

Other Noncontrolling Interests - Additional Information (Detail)	Mar. 31, 2015
	Store
Noncontrolling Interest in Operating Partnership [Line Items]
Number of operating stores owned by consolidated joint venture	19
Other [Member]
Noncontrolling Interest in Operating Partnership [Line Items]
Number of consolidated joint ventures	2
Other [Member] | Minimum [Member]
Noncontrolling Interest in Operating Partnership [Line Items]
Ownership interests of third party owners	1.00%
Other [Member] | Maximum [Member]
Noncontrolling Interest in Operating Partnership [Line Items]
Ownership interests of third party owners	3.30%

Equity_in_Earnings_of_Unconsol1

Equity in Earnings of Unconsolidated Real Estate Ventures - Gain on Sale of Real Estate and Purchase of Joint Venture Partners' Interests - Additional Information (Detail) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015
Schedule Of Results Related To Equity Accounted Investees [Line Items]
Ownership interest acquired in joint venture (as a percent)	82.40%
Cash paid for acquiring equity interest in the joint venture	$1,700
Company held mortgage notes receivable eliminated as a result of the acquisition	11,009
Equity ownership prior to the acquisition (as a percent)	17.60%
Non-cash gain	1,629
ESS PRISA II LLC [Member]
Schedule Of Results Related To Equity Accounted Investees [Line Items]
Ownership interest percentage	2.00%
Gain (loss) on sale of property	60,496
Percentage of gain from sale of property	2.00%
Gain (loss) from sale of property	1,228
ESS PRISA II LLC [Member] | NEW YORK
Schedule Of Results Related To Equity Accounted Investees [Line Items]
Number of operating stores sold by consolidated joint venture	1
Proceeds from sale of property	$90,000

Segment_Information_Additional

Segment Information - Additional Information (Detail)	3 Months Ended
	Mar. 31, 2015
	Segments
Segment Reporting [Abstract]
Number of reportable segments	3

Segment_Information_Schedule_o

Segment Information - Schedule of Financial Information of Business Segments (Detail) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Segment Reporting Information [Line Items]
Investment in unconsolidated real estate ventures	$85,602		$85,711
Total assets	4,464,145		4,402,107
Total revenues	173,154	152,587
Operating expenses, including depreciation and amortization	97,718	92,189
Income (loss) from operations	75,436	60,398
Interest expense	-21,431	-19,598
Interest income	856	269
Non-cash interest expense related to the amortization of discount on equity component of exchangeable senior notes	-697	-662
Interest income on note receivable from Preferred Operating Partnership unit holder	1,213	1,213
Equity in earnings of unconsolidated real estate ventures	2,650	2,419
Equity in earnings of unconsolidated real estate ventures - gain on sale of real assets and purchase of partners' interests	2,857
Income tax expense	-2,248	-2,830
Net income (loss)	58,636	41,209
Depreciation and amortization expense	30,428	28,375
Acquisition of real estate assets	-77,082	-253,939
Development and redevelopment of real estate assets	-3,140	-2,820
Rental Operations [Member]
Segment Reporting Information [Line Items]
Investment in unconsolidated real estate ventures	85,602		85,711
Total assets	4,194,744		4,109,673
Total revenues	148,894	132,001
Operating expenses, including depreciation and amortization	75,509	69,942
Income (loss) from operations	73,385	62,059
Interest expense	-21,830	-19,310
Equity in earnings of unconsolidated real estate ventures	2,650	2,419
Equity in earnings of unconsolidated real estate ventures - gain on sale of real assets and purchase of partners' interests	2,857
Income tax expense	-754	-434
Net income (loss)	56,308	44,734
Depreciation and amortization expense	28,265	26,460
Tenant Reinsurance [Member]
Segment Reporting Information [Line Items]
Total assets	38,745		39,383
Total revenues	16,510	13,463
Operating expenses, including depreciation and amortization	2,928	2,567
Income (loss) from operations	13,582	10,896
Interest income	4	4
Income tax expense	-1,874	-3,815
Net income (loss)	11,712	7,085
Property Management Acquisition and Development [Member]
Segment Reporting Information [Line Items]
Total assets	230,656		253,051
Total revenues	7,750	7,123
Operating expenses, including depreciation and amortization	19,281	19,680
Income (loss) from operations	-11,531	-12,557
Interest expense	399	-288
Interest income	852	265
Non-cash interest expense related to the amortization of discount on equity component of exchangeable senior notes	-697	-662
Interest income on note receivable from Preferred Operating Partnership unit holder	1,213	1,213
Income tax expense	380	1,419
Net income (loss)	-9,384	-10,610
Depreciation and amortization expense	2,163	1,915
Acquisition of real estate assets	-77,082	-253,939
Development and redevelopment of real estate assets	($3,140)	($2,820)

Commitments_and_Contingencies_

Commitments and Contingencies - Additional Information (Detail) (Contract Amount [Member], USD $)	Mar. 31, 2015
In Thousands, unless otherwise specified
Contract Amount [Member]
Commitments And Contingencies [Line Items]
Number of stores to be acquired	42
Number of stores scheduled to be closed	34
Purchase price	$374,283

Subsequent_Events_Additional_I

Subsequent Events - Additional Information (Detail) (USD $)	3 Months Ended	0 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Apr. 14, 2015	Apr. 15, 2015	7-May-15	Apr. 24, 2015	5-May-15
		Store	Store	Store	Store	Store
Subsequent Event [Line Items]
Payment for acquisition	$86,411
Texas [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Number of self-storage facilities (stores) acquired		1
Payment for acquisition		8,650
Arizona and Texas [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Number of self-storage facilities (stores) acquired			22
Payment for acquisition			177,700
Georgia [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Number of self-storage facilities (stores) acquired				1	1
Payment for acquisition				6,500	6,500
North Carolina [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Number of self-storage facilities (stores) acquired						1
Payment for acquisition						$11,000