CoreSite Realty 10-Q 1 Nov 13 2013 Q3 Quarterly report Financial data

Document_and_Entity_Informatio

Document and Entity Information	9 Months Ended
	Sep. 30, 2013	Oct. 30, 2013
Document and Entity Information	'	'
Entity Registrant Name	'CoreSite Realty Corp	'
Entity Central Index Key	'0001490892	'
Document Type	'10-Q	'
Document Period End Date	30-Sep-13	'
Amendment Flag	'false	'
Current Fiscal Year End Date	'--12-31	'
Entity Current Reporting Status	'Yes	'
Entity Filer Category	'Accelerated Filer	'
Entity Common Stock, Shares Outstanding	'	21,383,226
Document Fiscal Year Focus	'2013	'
Document Fiscal Period Focus	'Q3	'

CONDENSED_CONSOLIDATED_BALANCE

CONDENSED CONSOLIDATED BALANCE SHEETS (USD $)	Sep. 30, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
Investments in real estate:	'	'
Land	$76,227	$85,868
Building and building improvements	668,580	596,405
Leasehold improvements	92,996	85,907
Total investments in real estate	837,803	768,180
Less: Accumulated depreciation and amortization	-142,133	-105,433
Net investment in operating properties	695,670	662,747
Construction in progress	157,200	61,328
Net investments in real estate	852,870	724,075
Cash and cash equivalents	702	8,130
Accounts and other receivables, net of allowance for doubtful accounts of $320 and $625 as of September 30, 2013, and December 31, 2012, respectively	11,095	9,901
Lease intangibles, net of accumulated amortization of $20,026 and $33,050 as of September 30, 2013, and December 31, 2012, respectively	12,460	19,453
Goodwill	41,191	41,191
Other assets	47,583	42,582
Total assets	965,901	845,332
Liabilities:	'	'
Revolving credit facility	108,000	'
Mortgage loans payable	58,625	59,750
Accounts payable and accrued expenses	75,248	50,624
Deferred rent payable	9,579	4,329
Acquired below-market lease contracts, net of accumulated amortization of $5,702 and $10,062 as of September 30, 2013, and December 2012, respectively	7,050	8,539
Prepaid rent and other liabilities	11,697	11,317
Total liabilities	270,199	134,559
Stockholders' equity:	'	'
Series A Cumulative Preferred Stock 7.25%, $115,000 liquidation preference ($25.00 per share, $0.01 par value), 4,600,000 shares issued and outstanding as of September 30, 2013, and December 31, 2012	115,000	115,000
Common Stock, par value $0.01, 100,000,000 shares authorized and 21,412,432 and 21,202,673 shares issued and outstanding at September 30, 2013, and December 31, 2012, respectively	208	207
Additional paid-in capital	265,483	259,009
Distributions in excess of net income	-45,953	-35,987
Total stockholders' equity	334,738	338,229
Noncontrolling interests	360,964	372,544
Total equity	695,702	710,773
Total liabilities and equity	$965,901	$845,332

CONDENSED_CONSOLIDATED_BALANCE1

CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) (USD $)	9 Months Ended	12 Months Ended
In Thousands, except Share data, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
CONDENSED CONSOLIDATED BALANCE SHEETS	'	'
Allowance for doubtful accounts (in dollars)	$320	$625
Accumulated amortization, lease intangibles (in dollars)	20,026	33,050
Accumulated amortization, acquired below-market lease contracts (in dollars)	5,702	10,062
Series A Cumulative Preferred Stock, dividend rate (as a percent)	7.25%	7.25%
Series A Cumulative Preferred Stock, liquidation preference	$115,000	$115,000
Series A Cumulative Preferred Stock, liquidation preference (in dollars per share)	$25	$25
Series A Cumulative Preferred Stock, par value (in dollars per share)	$0.01	$0.01
Series A Cumulative Preferred Stock, shares issued	4,600,000	4,600,000
Series A Cumulative Preferred Stock, shares outstanding	4,600,000	4,600,000
Common Stock, par value (in dollars per share)	$0.01	$0.01
Common Stock, shares authorized	100,000,000	100,000,000
Common Stock, shares issued	21,412,432	21,202,673
Common Stock, shares outstanding	21,412,432	21,202,673

CONDENSED_CONSOLIDATED_STATEME

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS (USD $)	3 Months Ended		9 Months Ended
In Thousands, except Share data, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Operating revenues:	'	'	'	'
Rental revenue	$35,283	$31,603	$102,590	$91,837
Power revenue	15,979	14,230	43,994	39,543
Interconnection revenue	7,441	6,177	21,066	15,268
Tenant reimbursement and other	1,932	1,752	5,743	5,034
Total operating revenues	60,635	53,762	173,393	151,682
Operating expenses:	'	'	'	'
Property operating and maintenance	17,368	16,360	47,013	46,029
Real estate taxes and insurance	2,226	2,158	6,750	6,304
Depreciation and amortization	16,424	16,583	48,634	47,991
Sales and marketing	3,206	2,231	10,931	6,941
General and administrative	7,045	6,389	20,225	18,777
Rent	5,082	4,689	14,631	13,957
Transaction costs	25	293	279	576
Total operating expenses	51,376	48,703	148,463	140,575
Operating income	9,259	5,059	24,930	11,107
Interest income	14	5	18	12
Interest expense	-708	-1,595	-1,930	-3,922
Income before income taxes	8,565	3,469	23,018	7,197
Income tax expense	-56	-522	-435	-1,059
Net income	8,509	2,947	22,583	6,138
Net income attributable to noncontrolling interests	3,524	1,627	8,962	3,389
Net income attributable to CoreSite Realty Corporation	4,985	1,320	13,621	2,749
Preferred stock dividends	-2,084	'	-6,253	'
Net income attributable to common shares	$2,901	$1,320	$7,368	$2,749
Net income per share attributable to common shares:	'	'	'	'
Basic (in dollars per share)	$0.14	$0.06	$0.35	$0.13
Diluted (in dollars per share)	$0.14	$0.06	$0.34	$0.13
Weighted average common shares outstanding	'	'	'	'
Basic (in shares)	20,871,504	20,554,893	20,793,596	20,514,713
Diluted (in shares)	21,479,971	21,027,635	21,465,710	20,890,894

CONDENSED_CONSOLIDATED_STATEME1

CONDENSED CONSOLIDATED STATEMENT OF EQUITY (USD $)	Total	Total Stockholders' Equity	Preferred Stock	Common Shares	Additional Paid-in Capital	Distributions in Excess of Net Income	Noncontrolling Interests
In Thousands, except Share data, unless otherwise specified
Balance at Dec. 31, 2012	$710,773	$338,229	$115,000	$207	$259,009	($35,987)	$372,544
Balance (in shares) at Dec. 31, 2012	'	'	'	21,202,673	'	'	'
Increase (Decrease) in Stockholders' Equity	'	'	'	'	'	'	'
Issuance of restricted stock awards, net of forfeitures	1	1	'	1	'	'	'
Issuance of restricted stock awards, net of forfeitures (in shares)	'	'	'	169,482	'	'	'
Exercise of stock options	630	630	'	'	630	'	'
Exercise of stock options (in shares)	'	'	'	40,277	'	'	'
Offering costs	-27	-27	'	'	-27	'	'
Amortization of deferred compensation	5,871	5,871	'	'	5,871	'	'
Dividends declared on preferred stock	-6,253	-6,253	'	'	'	-6,253	'
Dividends and distributions	-37,876	-17,334	'	'	'	-17,334	-20,542
Net income	22,583	13,621	'	'	'	13,621	8,962
Balance at Sep. 30, 2013	$695,702	$334,738	$115,000	$208	$265,483	($45,953)	$360,964
Balance (in shares) at Sep. 30, 2013	'	'	'	21,412,432	'	'	'

CONDENSED_CONSOLIDATED_STATEME2

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (USD $)	9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012
CASH FLOWS FROM OPERATING ACTIVITIES	'	'
Net income	$22,583	$6,138
Adjustments to reconcile net income to net cash provided by operating activities:	'	'
Depreciation and amortization	48,634	47,991
Amortization of above/below market leases	-672	-1,241
Amortization of deferred financing costs	1,293	1,307
Amortization of share-based compensation	5,337	4,083
Bad debt expense	241	276
Changes in operating assets and liabilities:	'	'
Accounts receivable	-1,435	-3,559
Deferred rent receivable	-1,660	-3,262
Deferred leasing costs	-5,373	-2,936
Other assets	-2,713	1,000
Accounts payable and accrued expenses	3,361	1,206
Prepaid rent and other liabilities	380	-3,883
Deferred rent payable	5,250	663
Net cash provided by operating activities	75,226	47,783
CASH FLOWS FROM INVESTING ACTIVITIES	'	'
Tenant improvements	-5,214	-5,266
Real estate improvements	-117,964	-50,276
Acquisition of NY2	-21,889	'
Acquisition of Comfluent, net of cash received	'	-2,581
Changes in reserves for capital improvements	'	8,690
Net cash used in investing activities	-145,067	-49,433
CASH FLOWS FROM FINANCING ACTIVITIES	'	'
Proceeds from exercise of stock options	630	874
Offering costs	-27	'
Proceeds from revolving credit facility	108,000	57,750
Principal payments on mortgage loans	-1,125	-25,233
Payments of loan fees and costs	-2,621	-119
Dividends and distributions paid on common stock and OP units	-37,508	-24,829
Dividends paid on preferred stock	-4,936	'
Net cash provided by financing activities	62,413	8,443
Net change in cash and cash equivalents	-7,428	6,793
Cash and cash equivalents, beginning of period	8,130	6,628
Cash and cash equivalents, end of period	702	13,421
SUPPLEMENTAL DISCLOSURE OF CASH FLOW INFORMATION	'	'
Cash paid for interest	3,205	4,092
NON-CASH INVESTING AND FINANCING ACTIVITY	'	'
Construction costs payable capitalized to real estate	32,291	11,891
Accrual of dividends and distributions	$15,051	$8,640

Organization_and_Description_o

Organization and Description of Business	9 Months Ended
	Sep. 30, 2013
Organization and Description of Business	'
Organization and Description of Business	'
	1. Organization and Description of Business
	CoreSite Realty Corporation, through its controlling interest in CoreSite, L.P. (the “Operating Partnership”) and the subsidiaries of the Operating Partnership (collectively, the “Company,” “we,” or “our”), is a fully-integrated, self-administered, and self-managed real estate investment trust (“REIT”). The Company was organized in the State of Maryland on February 17, 2010, completed its initial public offering of common stock (the “IPO”) on September 28, 2010, and is the sole general partner of the Operating Partnership. As of September 30, 2013, the Company owns a 45.1% common interest in the Operating Partnership.
	We are engaged in the business of owning, acquiring, constructing and managing technology-related real estate and as of September 30, 2013, our property portfolio included 14 operating data center facilities and multiple development projects located in some of the largest and fastest growing data center markets in the United States, including Los Angeles, the San Francisco Bay and Northern Virginia areas, Chicago, Boston, New York City, Miami and Denver. The development projects include construction of new facilities in the San Francisco Bay, Northern Virginia and New York areas.

Summary_of_Significant_Account

Summary of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2013
Summary of Significant Accounting Policies	'
Summary of Significant Accounting Policies	'
	2. Summary of Significant Accounting Policies
	Principles of Consolidation and Basis of Presentation
	The accompanying unaudited condensed consolidated financial statements have been prepared by our management in accordance with U.S. generally accepted accounting principles (“GAAP”) for interim financial information and in compliance with the rules and regulations of the United States Securities and Exchange Commission. Accordingly, these condensed consolidated financial statements do not include all of the information and footnotes required by GAAP for complete financial statements. In the opinion of our management, all adjustments (consisting of normal recurring adjustments) considered necessary for a fair presentation have been included. The results of operations for the nine months ended September 30, 2013, are not necessarily indicative of the expected results for the year ending December 31, 2013. These condensed consolidated financial statements should be read in conjunction with the audited consolidated financial statements and the notes thereto included in our Annual Report on Form 10-K for the year ended December 31, 2012. Intercompany balances and transactions have been eliminated.
	Use of Estimates
	The preparation of these condensed consolidated financial statements in conformity with GAAP requires our management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingencies at the date of the condensed consolidated financial statements and the reported amounts of revenues and expenses during the reporting period. We evaluate our estimates, including those related to assessing the carrying values of our real estate properties, accrued liabilities, and performance-based equity compensation plans. We base our estimates on historical experience, current market conditions, and various other assumptions that we believe to be reasonable under the circumstances. Actual results may vary from those estimates and those estimates could vary under different assumptions or conditions.
	Adjustments and Reclassifications
	Interconnection revenue, included on the condensed consolidated statements of operations, and cash used for tenant improvement investing activities, included in the accompanying condensed consolidated statements of cash flows for 2012, have been reclassified to conform to the 2013 financial statement presentation. In addition, certain other immaterial amounts included in the condensed consolidated financial statements for 2012 have been reclassified to conform to the 2013 financial statement presentation.
	Investments in Real Estate
	Real estate investments are carried at cost less accumulated depreciation and amortization. The cost of real estate includes the purchase price of the property and leasehold improvements. Expenditures for maintenance and repairs are expensed as incurred. Significant renovations and betterments that extend the economic useful lives of assets are capitalized. During land development and construction periods, we capitalize construction costs, legal fees, financing costs, real estate taxes and insurance and internal costs of personnel performing development, if such costs are incremental and identifiable to a specific development project. Capitalization begins upon commencement of development efforts and ceases when the property is ready for its intended use and held available for occupancy. Interest is capitalized during the period of development based upon applying the weighted-average borrowing rate to the actual development costs expended. Capitalized interest costs were $1.1 million and $0.3 million for the three months ended September 30, 2013, and 2012, respectively, and $3.0 million and $1.5 million for the nine months ended September 30, 2013, and 2012, respectively.
	Depreciation and amortization are calculated using the straight-line method over the following useful lives of the assets:
	Buildings	27 to 40 years
	Building improvements	1 to 15 years
	Leasehold improvements	The shorter of the lease term or useful life of the asset
	Depreciation expense was $13.7 million and $10.7 million for the three months ended September 30, 2013, and 2012, respectively, and $38.9 million and $29.7 million for the nine months ended September 30, 2013, and 2012, respectively.
	Acquisition of Investment in Real Estate
	Purchase accounting is applied to the assets and liabilities related to all real estate investments acquired. The fair value of the real estate acquired is allocated to the acquired tangible assets, consisting primarily of land, building and improvements, and identified intangible assets and liabilities, consisting of the value of above-market and below-market leases, value of in-place leases and the value of customer relationships.
	The fair value of the land and building of an acquired property is determined by valuing the property as if it were vacant, and the “as-if-vacant” fair value is then allocated to land and building based on management’s determination of the fair values of these assets. Management determines the as-if-vacant fair value of a property using methods similar to those used by independent appraisers. Factors considered by management in performing these analyses include an estimate of carrying costs during the expected lease-up periods considering current market conditions and costs to execute similar leases.
	The fair value of intangibles related to in-place leases includes the value of lease intangibles for above-market and below-market leases, lease origination costs, and customer relationships, determined on a lease-by-lease basis. Above-market and below-market leases are valued based on the present value (using an interest rate which reflects the risks associated with the leases acquired) of the difference between (i) the contractual amounts to be paid pursuant to the in-place leases and (ii) management’s estimate of fair market lease rates for the corresponding in-place leases, measured over a period equal to the remaining non-cancelable term of the lease and, for below-market leases, over a period equal to the initial term plus any below-market fixed rate renewal periods. Lease origination costs include estimates of costs avoided associated with leasing the property, including tenant allowances and improvements and leasing commissions. Customer relationship intangibles relate to the additional revenue opportunities expected to be generated through interconnection services and utility services to be provided to the in-place lease tenants.
	The capitalized values for above and below-market lease intangibles, lease origination costs, and customer relationships are amortized over the term of the underlying leases or the expected customer relationship. Amortization related to above-market and below-market leases where the Company is the lessor is recorded as either a reduction of or an increase to rental income, amortization related to above-market and below-market leases where the Company is the lessee is recorded as either a reduction of or an increase to rent expense and amortization for lease origination costs and customer relationships are recorded as amortization expense. If a lease is terminated prior to its stated expiration, all unamortized amounts relating to that lease are written off. The carrying value of intangible assets is reviewed for impairment in connection with its respective asset group whenever events or changes in circumstances indicate that the asset group may not be recoverable. An impairment loss is recognized if the carrying amount of the asset group is not recoverable and its carrying amount exceeds its estimated fair value. No impairment loss was recognized for the three and nine months ended September 30, 2013, and 2012.
	The excess of the cost of an acquired business over the net of the amounts assigned to assets acquired (including identified intangible assets) and liabilities assumed is recorded as goodwill. As of September 30, 2013, and December 31, 2012, we had approximately $41.2 million of goodwill at each date. The Company’s goodwill has an indeterminate life and is not amortized, but is tested for impairment on an annual basis, or more frequently if events or changes in circumstances indicate that the asset might be impaired. No impairment loss was recognized for the three and nine months ended September 30, 2013, and 2012.
	Cash and Cash Equivalents
	Cash and cash equivalents include all non-restricted cash held in financial institutions and other non-restricted highly liquid short-term investments with original maturities at acquisition of three months or less.
	Deferred Costs
	Deferred leasing costs include commissions and other direct and incremental costs incurred to obtain new customer leases, which are capitalized and amortized over the terms of the related leases using the straight-line method. If a lease terminates prior to the expiration of its initial term, any unamortized costs related to the lease are written off to amortization expense.
	Deferred financing costs include costs incurred in connection with obtaining debt and extending existing debt. These financing costs are capitalized and amortized on a straight-line basis, which approximates the effective-interest method, over the term of the loan and are included as a component of interest expense.
	Recoverability of Long-Lived Assets
	The Company reviews its long-lived assets for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable. Impairment is recognized when estimated expected future cash flows (undiscounted and without interest charges) are less than the carrying amount of the assets. The estimation of expected future net cash flows is inherently uncertain and relies, to a considerable extent, on assumptions regarding current and future economics and market conditions and the availability of capital. If, in future periods, there are changes in the estimates or assumptions incorporated into the impairment review analysis, the changes could result in an adjustment to the carrying amount of the long-lived assets. To the extent that impairment has occurred, the excess of the carrying amount of long-lived assets over its estimated fair value would be recognized as an impairment loss charged to net income. For the three and nine months ended September 30, 2013, and 2012, no impairment was recognized.
	Revenue Recognition
	All leases are classified as operating leases and minimum rents are recognized on a straight-line basis over the non-cancellable term of the agreements. The excess of rents recognized over amounts contractually due pursuant to the underlying leases are included in deferred rent receivable. If a lease terminates prior to its stated expiration, the deferred rent receivable relating to that lease is written off as a reduction of rental revenue.
	When arrangements include multiple elements, the revenue associated with separate elements is allocated based on the relative fair values of those elements. The revenue associated with each element is then recognized as earned. Interconnection services are considered as separate earnings processes that are provided and completed on a month-to-month basis and revenue is recognized in the period that services are performed. Set-up charges and utility installation fees are initially deferred and recognized over the term of the arrangement as revenue or the expected period of performance unless management determines a separate earnings process exists related to an installation charge.
	Tenant reimbursements for real estate taxes, common area maintenance, and other recoverable costs are recognized as revenue in the period that the related expenses are incurred.
	Above-market and below-market lease intangibles that were acquired are amortized on a straight-line basis as decreases and increases, respectively, to rental revenue over the remaining non-cancellable term of the underlying leases. For the three months ended September 30, 2013, and 2012, the net effect of amortization of acquired above-market and below-market leases resulted in an increase to rental revenue of $0.2 million and $0.4 million, respectively. For the nine months ended September 30, 2013, and 2012, the net effect of amortization of acquired above-market and below-market leases resulted in an increase to rental income of $0.5 million and $1.2 million, respectively.
	A provision for uncollectible accounts is recorded if a receivable balance relating to contractual rent, rent recorded on a straight-line basis, or tenant reimbursements is considered by management to be uncollectible. At September 30, 2013, and December 31, 2012, the allowance for doubtful accounts totaled $0.3 million and $0.6 million, respectively.
	Share-Based Compensation
	We account for share-based compensation using the fair value method of accounting. The estimated fair value of the stock options granted by us is calculated based on Black-Scholes option-pricing model and is amortized on a straight-line basis over the vesting period. The fair value of restricted share-based and Operating Partnership unit compensation is based on the market value of our common stock on the date of the grant and is amortized on a straight-line basis over the vesting period.
	Asset Retirement and Environmental Remediation Obligations
	We record accruals for estimated retirement and environmental remediation obligations. The obligations relate primarily to the removal of asbestos and contaminated soil during development of the properties as well as the estimated equipment removal costs upon termination of a certain lease where we are the lessee. At September 30, 2013, and December 31, 2012, the amount included in other liabilities on the condensed consolidated balance sheets was approximately $2.5 million and $2.6 million, respectively.
	Income Taxes
	We elected to be taxed as a REIT under the Internal Revenue Code of 1986, as amended (the “Code”), commencing with our taxable year ended December 31, 2010. To qualify as a REIT, we are required to distribute at least 90% of our taxable income to our stockholders and meet various other requirements imposed by the Code relating to such matters as operating results, asset holdings, distribution levels and diversity of stock ownership. Provided we qualify for taxation as a REIT, we are generally not subject to corporate level federal income tax on the earnings distributed currently to our stockholders. If we fail to qualify as a REIT in any taxable year, and are unable to avail ourselves of certain savings provisions set forth in the Code, all of our taxable income would be subject to federal income tax at regular corporate rates, including any applicable alternative minimum tax.
	To maintain REIT status, we must distribute a minimum of 90% of our taxable income. However, it is our policy and intent, subject to change, to distribute 100% of our taxable income and therefore no provision is required in the accompanying financial statements for federal income taxes with regards to activities of the REIT and its subsidiary pass-through entities. Any taxable income prior to the completion of the IPO is the responsibility of the Company’s prior member. The allocable share of income is included in the income tax returns of the members. The Company is subject to the statutory requirements of the locations in which it conducts business. State and local income taxes are accrued as deemed required in the best judgment of management based on analysis and interpretation of respective tax laws.
	We have elected to treat certain subsidiaries as taxable REIT subsidiaries (“TRS”). Certain activities that we undertake must be conducted by a TRS, such as services for our tenants that could be considered otherwise impermissible for us to perform and holding assets that we cannot hold directly. A TRS is subject to corporate level federal and state income taxes. Relative deferred tax assets and liabilities arising from temporary differences in financial reporting versus tax reporting are also established as determined by management.
	Deferred income taxes are recognized in certain taxable entities. Deferred income tax is generally a function of the period’s temporary differences (items that are treated differently for tax purposes than for financial reporting purposes), the utilization of tax net operating losses generated in prior years that previously had been recognized as deferred income tax assets and the reversal of any previously recorded deferred income tax liabilities. A valuation allowance for deferred income tax assets is provided if we believe all or some portion of the deferred income tax asset may not be realized. Any increase or decrease in the valuation allowance resulting from a change in circumstances that causes a change in the estimated realizability of the related deferred income tax asset is included in deferred tax expense. As of September 30, 2013, the deferred income taxes were not material.
	We currently have no liabilities for uncertain tax positions. The earliest tax year for which we are subject to examination is 2010.
	Concentration of Credit Risks
	Our cash and cash equivalents are maintained in various financial institutions, which, at times, may exceed federally insured limits. We have not experienced any losses in such accounts, and management believes that we are not exposed to any significant credit risk in this area. We have no off-balance sheet concentrations of credit risk, such as foreign exchange contracts, option contracts, or foreign currency hedging arrangements.
	Segment Information
	We manage our business as one reportable segment consisting of investments in data centers located in the United States. Although we provide services in several markets, these operations have been aggregated into one reportable segment based on the similar economic characteristics amongst all markets, including the nature of the services provided and the type of customers purchasing these services.

Investment_in_Real_Estate

Investment in Real Estate	9 Months Ended
	Sep. 30, 2013
Investment in Real Estate	'
Investment in Real Estate	'
	3. Investment in Real Estate
	On February 7, 2013, the Company acquired land and a vacant building, NY2, in Secaucus, New Jersey, with a total real estate value of $23.0 million. NY2 is being developed into a data center facility. In addition to NY2, during the nine months ended September 30, 2013, the Company commenced development on two other data center facilities, VA2, in Reston, Virginia, and SV5, in Santa Clara, California. Based on the relative fair values of the parcels, land was allocated to each of VA2 and SV5 and was reclassified during the first quarter of 2013 to construction in progress in the condensed consolidated balance sheets. The reclassification equaled $5.2 million and $2.4 million for VA2 and SV5, respectively.
	The following is a summary of the properties owned and leased at September 30, 2013 (in thousands):
	Property Name	Location	Land		Buildings and		Leasehold		Construction		Total Cost
					Improvements		Improvements		in Progress
	SV1	San Jose, CA	$	6,863	$	114,425	$	—	$	4,607	$	125,895
	SV2	Milpitas, CA	5,086		23,780		—		271		29,137
	SV3	Santa Clara, CA	3,972		45,821		—		130		49,923
	SV4	Santa Clara, CA	4,442		85,671		—		942		91,055
	SV5	Santa Clara, CA	—		—		—		21,178		21,178
	Santa Clara Campus(1)	Santa Clara, CA	8,173		8,221		—		9,055		25,449
	BO1	Somerville, MA	6,100		77,388		—		2,900		86,388
	NY1	New York, NY	—		—		32,522		180		32,702
	NY2	Secaucus, NJ	—		—		—		78,563		78,563
	VA1	Reston, VA	6,903		105,658		—		3,487		116,048
	VA2	Reston, VA	—		—		—		22,227		22,227
	DC1	Washington, DC	—		—		7,264		262		7,526
	CH1	Chicago, IL	5,493		75,951		—		5,415		86,859
	LA1	Los Angeles, CA	—		—		51,830		2,363		54,193
	LA2	Los Angeles, CA	28,467		121,819		—		5,486		155,772
	MI1	Miami, FL	728		9,846		—		118		10,692
	DE1	Denver, CO	—		—		711		15		726
	DE2	Denver, CO	—		—		669		1		670
	Total		$	76,227	$	668,580	$	92,996	$	157,200	$	995,003
	(1)    This campus includes office and light-industrial real estate buildings and land held for development in Santa Clara, CA.

Other_Assets

Other Assets	9 Months Ended
	Sep. 30, 2013
Other Assets	'
Other Assets	'
	4. Other Assets
	Our other assets consisted of the following, net of amortization and depreciation, if applicable, as of September 30, 2013, and December 31, 2012 (in thousands):
		September 30,		December 31,
		2013		2012
	Deferred leasing costs	$	13,012	$	12,444
	Deferred rent receivable	16,677		15,017
	Deferred financing costs	3,758		2,520
	Corporate furniture, fixtures and equipment	4,689		4,152
	Other	9,447		8,449
	Total	$	47,583	$	42,582

Debt

Debt	9 Months Ended
	Sep. 30, 2013
Debt	'
Debt	'
	5. Debt
	A summary of outstanding indebtedness as of September 30, 2013, and December 31, 2012 is as follows (in thousands):
				Maturity	September 30,		December 31,
		Interest Rate		Date	2013		2012
	SV1 - Mortgage loan	3.69% and 3.71% at September 30, 2013, and December 31, 2012, respectively		October 9, 2014	$	58,625	$	59,750
	Revolving credit facility	2.18% and 2.46% at September 30, 2013, and December 31, 2012, respectively		January 3, 2017	108,000		—
	Total principal outstanding				$	166,625	$	59,750
	SV1 Mortgage Loan
	As of September 30, 2013, SV1 was subject to a $58.6 million mortgage loan with a maturity date of October 9, 2014. The loan bears variable interest and requires the payment of interest and principal until maturity. The mortgage requires ongoing compliance by us with various covenants, including liquidity and net operating income covenants. As of September 30, 2013, we were in compliance with the covenants under the mortgage.
	Revolving Credit Facility
	On January 3, 2013, our Operating Partnership and certain subsidiary co-borrowers entered into a second amended and restated senior unsecured revolving credit facility (the “Second Amended and Restated Credit Agreement”) with a group of lenders for which KeyBank National Association acts as administrative agent. The Second Amended and Restated Credit Agreement amended the Operating Partnership’s senior secured revolving credit facility, dated December 15, 2011 (the “Prior Facility”), and provides for the release of the properties owned by the Operating Partnership’s wholly owned subsidiaries from the existing liens in favor of the credit facility lenders, with the facility continuing on an unsecured basis and unconditionally guaranteed on a senior unsecured basis by the Company. Our Operating Partnership acts as the parent borrower, and our subsidiaries that own or lease real estate properties, are co-borrowers under the Second Amended and Restated Credit Agreement.
	The Second Amended and Restated Credit Agreement increased the commitment from the Prior Facility of $225.0 million to $355.0 million and extended the initial maturity date of the Prior Facility from December 15, 2014, to January 3, 2017, with a one-time extension option, which, if exercised, would extend the maturity date to January 3, 2018. The exercise of the extension option is subject to the payment of an extension fee equal to 25 basis points of the total commitment under the Second Amended and Restated Credit Agreement at initial maturity and certain other customary conditions. The Second Amended and Restated Credit Agreement contains an accordion feature, which allows our Operating Partnership to increase the total commitment by $145.0 million, to $500.0 million, under specified circumstances.
	On June 28, 2013, the borrowers under the Second Amended and Restated Credit Agreement partially exercised the accordion feature to increase the aggregate commitments by $50.0 million. As a result of the accordion exercise, the borrowing capacity increased from $355.0 million to $405.0 million. All other terms of the Second Amended and Restated Credit Agreement remain unchanged.
	Under the Second Amended and Restated Credit Agreement, our Operating Partnership may elect to have borrowings bear interest at a rate per annum equal to (i) LIBOR plus 200 basis points to 275 basis points, or (ii) a base rate plus 100 basis points to 175 basis points, each depending on our Operating Partnership’s leverage ratio.
	The total amount available for borrowings under the Second Amended and Restated Credit Agreement is subject to the lesser of the facility amount or the availability calculated based on our unencumbered asset pool. As of September 30, 2013, $396.6 million was available for us to borrow under the Second Amended and Restated Credit Agreement, of which $108.0 million was borrowed and outstanding.
	Our ability to borrow under the Second Amended and Restated Credit Agreement is subject to ongoing compliance with a number of financial covenants and other customary restrictive covenants, including, among others:
	·                  a maximum leverage ratio (defined as consolidated total indebtedness to total gross asset value) of 60%. As of September 30, 2013, our leverage ratio was 11.5%;
	·                  a maximum secured debt ratio (defined as consolidated total secured debt to total gross asset value) of 40%. As of September 30, 2013, our secured debt ratio was 3.8%;
	·                  a minimum fixed charge coverage ratio (defined as adjusted consolidated earnings before interest, taxes, depreciation and amortization to consolidated fixed charges) of 1.75 to 1.0. As of September 30, 2013, our fixed charge coverage ratio was 7.5 to 1.0; and
	·                  a maximum unhedged variable rate debt ratio (defined as unhedged variable rate indebtedness to gross asset value) of 30%. As of September 30, 2013, our unhedged variable rate debt ratio was 10.8%.
	As of September 30, 2013, we were in compliance with the covenants under our Second Amended and Restated Credit Agreement.
	Debt Maturities
	The following table summarizes the amount of our outstanding debt when such debt currently becomes due (in thousands):
	Year Ending December 31,
	Remainder of 2013	$	375
	2014	58,250
	2015	—
	2016	—
	2017	108,000
	Total	$	166,625

Stockholders_Equity

Stockholders' Equity	9 Months Ended
	Sep. 30, 2013
Stockholders' Equity	'
Stockholders' Equity	'
	6. Stockholders’ Equity
	We have declared the following dividends per share on our Series A Cumulative Preferred Stock and common shares during the nine months ended September 30, 2013:
	Declaration Date	Record Date	Payment Date	Preferred Stock			Common Shares
	March 5, 2013	March 28, 2013	April 15, 2013	$	0.62	-1	$	0.27
	May 24, 2013	June 28, 2013	July 15, 2013	0.4531		-2	0.27
	August 30, 2013	September 30, 2013	October 15, 2013	0.4531		-3	0.27
				$	1.5262		$	0.81
	(1) Dividend covers the period from the issuance of our Series A Cumulative Preferred Stock, December 12, 2012, to April 14, 2013.
	(2) Dividend covers the period from April 15, 2013, to July 14, 2013.
	(3) Dividend covers the period from July 15, 2013, to October 14, 2013.

Noncontrolling_Interests_Opera

Noncontrolling Interests - Operating Partnership	9 Months Ended
	Sep. 30, 2013
Noncontrolling Interests - Operating Partnership	'
Noncontrolling Interests - Operating Partnership	'
	7. Noncontrolling Interests — Operating Partnership
	Noncontrolling interests represent the limited partnership interests in the Operating Partnership held by individuals and entities other than CoreSite Realty Corporation. Since September 28, 2011, the current holders of Common Operating Partnership units have been eligible to have the Common Operating Partnership units redeemed for cash or, at our option, exchangeable into our common stock on a one-for-one basis. We have evaluated whether we control the actions or events necessary to issue the maximum number of shares that could be required to be delivered under the share settlement of the Common Operating Partnership units. Based on the results of this analysis, we concluded that the Common Operating Partnership units met the criteria to be classified within equity at September 30, 2013.
	The following table shows the ownership interest in the Operating Partnership as of September 30, 2013, and December 31, 2012:
		September 30, 2013			December 31, 2012
		Number of Units	Percentage of Total		Number of Units	Percentage of Total
	The Company	20,872,386	45.1	%	20,610,523	44.8	%
	Noncontrolling interests consist of:
	Common units held by third parties	25,275,390	54.7	%	25,275,390	55	%
	Incentive units held by employees	85,457	0.2	%	78,319	0.2	%
	Total	46,233,233	100	%	45,964,232	100	%
	For each share of common stock issued by the Company, the Operating Partnership issues an equivalent Common Operating Partnership unit to the Company. During the nine months ended September 30, 2013, the Company issued 262,665 shares of common stock related to employee compensation arrangements and, therefore, an equivalent number of Common Operating Partnership units were issued to the Company by the Operating Partnership.
	Holders of Common Operating Partnership units of record as of March 28, 2013, June 28, 2013, and September 30, 2013, received quarterly distributions of $0.27 per unit payable in correlation with declared dividends on common shares.
	On December 12, 2012, the Operating Partnership issued 4.6 million Preferred Operating Partnership units to the Company in connection with our issuance of Series A Cumulative Preferred Stock. The Preferred Operating Partnership units rank senior to the Common Operating Partnership units held by the Company and noncontrolling interests.
	The redemption value of the noncontrolling interests at September 30, 2013, was $860.7 million based on the closing price of the Company’s stock of $33.94 on September 30, 2013, the last trading day of the quarter.

Equity_Incentive_Plan

Equity Incentive Plan	9 Months Ended
	Sep. 30, 2013
Equity Incentive Plan	'
Equity Incentive Plan	'
	8. Equity Incentive Plan
	In connection with our IPO, the Company’s Board of Directors adopted the 2010 Equity Incentive Plan (as amended, the “2010 Plan”). The 2010 Plan is administered by the Board of Directors, or the plan administrator. Awards issuable under the 2010 Plan include common stock, stock options, restricted stock, stock appreciation rights, dividend equivalents and other incentive awards. Following approval by the Board of Directors on March 30, 2013, our stockholders, on May 22, 2013, approved the amendment and restatement of the 2010 Plan which, among other things, increased the number of shares of common stock authorized for issuance by 3,000,000 shares. We have reserved a total of 6,000,000 shares of our common stock for issuance pursuant to the 2010 Plan, which may be adjusted for changes in our capitalization and certain corporate transactions. To the extent that an award expires, terminates or lapses, or an award is settled in cash without the delivery of shares of common stock to the participant, then any unexercised shares subject to the award will be available for future grant or sale under the 2010 Plan. Shares of restricted stock which are forfeited or repurchased by us pursuant to the 2010 Plan may again be optioned, granted or awarded under the 2010 Plan. The payment of dividend equivalents in cash in conjunction with any outstanding awards will not be counted against the shares available for issuance under the 2010 Plan.
	As of September 30, 2013, 3,632,820 shares of our common stock were available for issuance pursuant to the 2010 Plan.
	Stock Options
	Stock option awards are granted with an exercise price equal to the closing market price of the Company’s common stock at the date of grant. The fair value of each option granted under the 2010 Plan is estimated on the date of grant using the Black-Scholes option-pricing model. For the nine months ended September 30, 2013, options to purchase 209,268 shares of common stock were granted. The fair values are being amortized on a straight-line basis over the vesting periods.
	The following table sets forth the stock option activity under the 2010 Plan for the nine months ended September 30, 2013:
		Number of		Weighted
		Shares Subject		Average
		to Option		Exercise Price
	Options outstanding, December 31, 2012	1,017,195		$	17.25
	Granted	209,268		32.5
	Forfeited	(23,865	)	21.22
	Exercised	(40,277	)	15.65
	Options outstanding, September 30, 2013	1,162,321		$	19.97
	The following table sets forth the number of shares subject to options that are unvested as of September 30, 2013, and the fair value of these options at the grant date:
		Number of		Weighted
		Shares Subject		Average Fair
		to Option		Value at Grant
	Unvested balance, December 31, 2012	730,159		$	5.7
	Granted	209,268		10.01
	Forfeited	(23,865	)	6.69
	Vested	(261,862	)	5.55
	Unvested balance, September 30, 2013	653,700		$	7.11
	As of September 30, 2013, total unearned compensation on options was approximately $3.9 million, and the weighted-average vesting period was 2.2 years.
	Restricted Awards
	During the nine months ended September 30, 2013, the Company granted 187,186 shares of restricted stock under the 2010 Plan. Additionally, the Company granted 5,328 restricted stock units, or RSUs under the 2010 Plan. The principal difference between these instruments is that RSUs are not outstanding shares of the Company’s common stock and do not have any of the rights or privileges thereof, including voting rights. On the applicable vesting date, the holder of an RSU becomes entitled to one share of common stock for each RSU. Restricted awards are amortized on a straight-line basis over the vesting period. The following table sets forth the number of unvested restricted awards and the weighted average fair value of these awards at the date of grant:
		Restricted		Weighted
		Awards		Average Fair
				Value at Grant
	Unvested balance, December 31, 2012	598,695		$	21.37
	Granted	192,514		32.47
	Forfeited	(16,902	)	25.08
	Vested	(229,613	)	20.8
	Unvested balance, September 30, 2013	544,694		$	25.42
	As of September 30, 2013, total unearned compensation on restricted awards was approximately $11.3 million, and the weighted-average vesting period was 2.4 years.

Earnings_Per_Share

Earnings Per Share	9 Months Ended
	Sep. 30, 2013
Earnings Per Share	'
Earnings Per Share	'
	9. Earnings Per Share
	The following is a summary of basic and diluted income per share (in thousands, except share and per share amounts):
		Three Months Ended September 30,				Nine Months Ended September 30,
		2013		2012		2013		2012
	Net income attributable to common shares	$	2,901	$	1,320	$	7,368	$	2,749
	Weighted average common shares outstanding - basic	20,871,504		20,554,893		20,793,596		20,514,713
	Effect of potentially dilutive common shares:
	Stock options	391,398		267,831		388,889		225,520
	Unvested restricted awards	217,069		204,911		283,225		150,661
	Weighted average common shares outstanding - diluted	21,479,971		21,027,635		21,465,710		20,890,894
	Net income per share attributable to common shares
	Basic	$	0.14	$	0.06	$	0.35	$	0.13
	Diluted	$	0.14	$	0.06	$	0.34	$	0.13
	In the calculations above, we have excluded weighted-average potentially dilutive securities of 211,721 and 200,908 for the three months ended September 30, 2013, and 2012, respectively, and 166,732 and 100,587 for the nine months ended September 30, 2013, and 2012, respectively, as their effect would have been antidilutive.

Estimated_Fair_Value_of_Financ

Estimated Fair Value of Financial Instruments	9 Months Ended
	Sep. 30, 2013
Estimated Fair Value of Financial Instruments	'
Estimated Fair Value of Financial Instruments	'
	10. Estimated Fair Value of Financial Instruments
	Authoritative guidance issued by FASB establishes a hierarchy of valuation techniques based on the observability of inputs utilized in measuring assets and liabilities at fair values. This hierarchy establishes market-based or observable inputs as the preferred source of values, followed by valuation models using management assumptions in the absence of market inputs. The three levels of the hierarchy under the authoritative guidance are as follows:
	Level 1 — Quoted prices (unadjusted) in active markets for identical assets or liabilities that the reporting entity can access at the assessment date.
	Level 2 — Inputs other than quoted prices included within Level 1 that are observable for the asset or liability, either directly or indirectly.
	Level 3 — Unobservable inputs for the asset or liability.
	Our financial instruments consist of cash and cash equivalents, restricted cash, accounts and other receivables, revolving credit facility, mortgage loans payable, interest payable and accounts payable. The carrying values of cash and cash equivalents, restricted cash, accounts and other receivables, interest payable and accounts payable approximate fair values due to the short-term nature of these financial instruments.
	The total balance of our mortgage loan payable and revolving credit facility was $166.6 million and $59.8 million as of September 30, 2013, and December 31, 2012, respectively, with a fair value that approximated book value at both periods, based on Level 3 inputs from the fair value hierarchy. Under the discounted cash flow method, the fair values of mortgage notes payable and the revolving credit facility are based on the Company’s assumptions of interest rates and terms available incorporating the Company’s credit risk.

Related_Party_Transactions

Related Party Transactions	9 Months Ended
	Sep. 30, 2013
Related Party Transactions	'
Related Party Transactions	'
	11. Related Party Transactions
	We lease 1,520 net rentable square feet of space at VA1 to an affiliate of The Carlyle Group (Carlyle). Affiliates of Carlyle own a 54.7% common interest in the Operating Partnership. Rental revenue was $0.1 million for the three ended September 30, 2013, and 2012, and $0.2 million for the nine months ended September 30, 2013, and 2012.

Commitments_and_Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 30, 2013
Commitments and Contingencies	'
Commitments and Contingencies	'
	12. Commitments and Contingencies
	As of September 30, 2013, the Company, as lessee, leases data center space under noncancelable operating lease agreements at LA1, DC1, DE1, DE2 and NY1, and its headquarters located in Denver, Colorado, under noncancelable operating lease agreements. The lease agreements provide for base rental rate increases at defined intervals during the terms of the leases. In addition, the Company has negotiated rent abatement periods to better match the phased build-out of the data center space. The Company accounts for such abatements and increasing base rentals using the straight-line method over the noncancelable terms of the leases. The difference between the straight-line expense and the cash payment is recorded as deferred rent payable. Rent expense on operating leases for the three months ended September 30, 2013, and 2012, was $5.1 million and $4.7 million, respectively, and for the nine months ended September 30, 2013, and 2012 was $14.6 million and $14.0 million, respectively. Additionally, the Company has commitments related to telecommunications capacity used to connect data centers located within the same market or geographical area and power usage. The following table summarizes our contractual obligations as of September 30, 2013 (in thousands):
		Remainder of
	Obligation	2013		2014		2015		2016		2017		Thereafter		Total
	Operating leases	$	4,644	$	18,902	$	19,258	$	18,942	$	17,503	$	80,893	$	160,142
	Credit Facility(1)	588		2,353		2,353		2,353		108,000		—		115,647
	Mortgages payable (2)	913		59,843		—		—		—		—		60,756
	Construction Contracts (3)	75,808		429		—		—		—		—		76,237
	Other (4)	1,441		1,536		1,071		564		176		1,484		6,272
	Total	$	83,394	$	83,063	$	22,682	$	21,859	$	125,679	$	82,377	$	419,054
	(1) Includes $108.0 million outstanding and estimated annual interest payments assuming no draws or payments on the revolving credit facility through the maturity date of January 3, 2017. The revolving credit facility is subject to variable rates and we estimated interest payments based on the interest rate as of September 30, 2013.
	(2) Includes $58.6 million of mortgage principal payments and estimated interest payments until debt maturity on October 9, 2014. We estimated interest payments of $0.5 million for the remainder of 2013 and $1.6 million in 2014. The mortgage payable is subject to variable rates and we estimated interest payments based on the interest rate as of September 30, 2013.
	(3) Obligations for construction contracts for properties under construction, tenant related capital expenditures, and other capital improvements.
	(4) Obligations for power contracts, telecommunications leases, and internal system development.
	From time to time, we are party to a variety of legal proceedings arising in the ordinary course of business. We believe that, with respect to any such matters to which we currently are a party, the ultimate disposition of any such matter will not result in a material adverse effect on our business, financial condition, cash flows or results of operations.

Summary_of_Significant_Account1

Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2013
Summary of Significant Accounting Policies	'
Principles of Consolidation and Basis of Presentation	'
	Principles of Consolidation and Basis of Presentation
	The accompanying unaudited condensed consolidated financial statements have been prepared by our management in accordance with U.S. generally accepted accounting principles (“GAAP”) for interim financial information and in compliance with the rules and regulations of the United States Securities and Exchange Commission. Accordingly, these condensed consolidated financial statements do not include all of the information and footnotes required by GAAP for complete financial statements. In the opinion of our management, all adjustments (consisting of normal recurring adjustments) considered necessary for a fair presentation have been included. The results of operations for the nine months ended September 30, 2013, are not necessarily indicative of the expected results for the year ending December 31, 2013. These condensed consolidated financial statements should be read in conjunction with the audited consolidated financial statements and the notes thereto included in our Annual Report on Form 10-K for the year ended December 31, 2012. Intercompany balances and transactions have been eliminated.
Use of Estimates	'
	Use of Estimates
	The preparation of these condensed consolidated financial statements in conformity with GAAP requires our management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingencies at the date of the condensed consolidated financial statements and the reported amounts of revenues and expenses during the reporting period. We evaluate our estimates, including those related to assessing the carrying values of our real estate properties, accrued liabilities, and performance-based equity compensation plans. We base our estimates on historical experience, current market conditions, and various other assumptions that we believe to be reasonable under the circumstances. Actual results may vary from those estimates and those estimates could vary under different assumptions or conditions.
Adjustments and Reclassifications	'
	Adjustments and Reclassifications
	Interconnection revenue, included on the condensed consolidated statements of operations, and cash used for tenant improvement investing activities, included in the accompanying condensed consolidated statements of cash flows for 2012, have been reclassified to conform to the 2013 financial statement presentation. In addition, certain other immaterial amounts included in the condensed consolidated financial statements for 2012 have been reclassified to conform to the 2013 financial statement presentation.
Investments in Real Estate	'
	Investments in Real Estate
	Real estate investments are carried at cost less accumulated depreciation and amortization. The cost of real estate includes the purchase price of the property and leasehold improvements. Expenditures for maintenance and repairs are expensed as incurred. Significant renovations and betterments that extend the economic useful lives of assets are capitalized. During land development and construction periods, we capitalize construction costs, legal fees, financing costs, real estate taxes and insurance and internal costs of personnel performing development, if such costs are incremental and identifiable to a specific development project. Capitalization begins upon commencement of development efforts and ceases when the property is ready for its intended use and held available for occupancy. Interest is capitalized during the period of development based upon applying the weighted-average borrowing rate to the actual development costs expended. Capitalized interest costs were $1.1 million and $0.3 million for the three months ended September 30, 2013, and 2012, respectively, and $3.0 million and $1.5 million for the nine months ended September 30, 2013, and 2012, respectively.
	Depreciation and amortization are calculated using the straight-line method over the following useful lives of the assets:
	Buildings	27 to 40 years
	Building improvements	1 to 15 years
	Leasehold improvements	The shorter of the lease term or useful life of the asset
	Depreciation expense was $13.7 million and $10.7 million for the three months ended September 30, 2013, and 2012, respectively, and $38.9 million and $29.7 million for the nine months ended September 30, 2013, and 2012, respectively.
Acquisition of Investment in Real Estate	'
	Acquisition of Investment in Real Estate
	Purchase accounting is applied to the assets and liabilities related to all real estate investments acquired. The fair value of the real estate acquired is allocated to the acquired tangible assets, consisting primarily of land, building and improvements, and identified intangible assets and liabilities, consisting of the value of above-market and below-market leases, value of in-place leases and the value of customer relationships.
	The fair value of the land and building of an acquired property is determined by valuing the property as if it were vacant, and the “as-if-vacant” fair value is then allocated to land and building based on management’s determination of the fair values of these assets. Management determines the as-if-vacant fair value of a property using methods similar to those used by independent appraisers. Factors considered by management in performing these analyses include an estimate of carrying costs during the expected lease-up periods considering current market conditions and costs to execute similar leases.
	The fair value of intangibles related to in-place leases includes the value of lease intangibles for above-market and below-market leases, lease origination costs, and customer relationships, determined on a lease-by-lease basis. Above-market and below-market leases are valued based on the present value (using an interest rate which reflects the risks associated with the leases acquired) of the difference between (i) the contractual amounts to be paid pursuant to the in-place leases and (ii) management’s estimate of fair market lease rates for the corresponding in-place leases, measured over a period equal to the remaining non-cancelable term of the lease and, for below-market leases, over a period equal to the initial term plus any below-market fixed rate renewal periods. Lease origination costs include estimates of costs avoided associated with leasing the property, including tenant allowances and improvements and leasing commissions. Customer relationship intangibles relate to the additional revenue opportunities expected to be generated through interconnection services and utility services to be provided to the in-place lease tenants.
	The capitalized values for above and below-market lease intangibles, lease origination costs, and customer relationships are amortized over the term of the underlying leases or the expected customer relationship. Amortization related to above-market and below-market leases where the Company is the lessor is recorded as either a reduction of or an increase to rental income, amortization related to above-market and below-market leases where the Company is the lessee is recorded as either a reduction of or an increase to rent expense and amortization for lease origination costs and customer relationships are recorded as amortization expense. If a lease is terminated prior to its stated expiration, all unamortized amounts relating to that lease are written off. The carrying value of intangible assets is reviewed for impairment in connection with its respective asset group whenever events or changes in circumstances indicate that the asset group may not be recoverable. An impairment loss is recognized if the carrying amount of the asset group is not recoverable and its carrying amount exceeds its estimated fair value. No impairment loss was recognized for the three and nine months ended September 30, 2013, and 2012.
	The excess of the cost of an acquired business over the net of the amounts assigned to assets acquired (including identified intangible assets) and liabilities assumed is recorded as goodwill. As of September 30, 2013, and December 31, 2012, we had approximately $41.2 million of goodwill at each date. The Company’s goodwill has an indeterminate life and is not amortized, but is tested for impairment on an annual basis, or more frequently if events or changes in circumstances indicate that the asset might be impaired. No impairment loss was recognized for the three and nine months ended September 30, 2013, and 2012.
Cash and Cash Equivalents	'
	Cash and Cash Equivalents
	Cash and cash equivalents include all non-restricted cash held in financial institutions and other non-restricted highly liquid short-term investments with original maturities at acquisition of three months or less.
Deferred Costs	'
	Deferred Costs
	Deferred leasing costs include commissions and other direct and incremental costs incurred to obtain new customer leases, which are capitalized and amortized over the terms of the related leases using the straight-line method. If a lease terminates prior to the expiration of its initial term, any unamortized costs related to the lease are written off to amortization expense.
	Deferred financing costs include costs incurred in connection with obtaining debt and extending existing debt. These financing costs are capitalized and amortized on a straight-line basis, which approximates the effective-interest method, over the term of the loan and are included as a component of interest expense.
Recoverability of Long-Lived Assets	'
	Recoverability of Long-Lived Assets
	The Company reviews its long-lived assets for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable. Impairment is recognized when estimated expected future cash flows (undiscounted and without interest charges) are less than the carrying amount of the assets. The estimation of expected future net cash flows is inherently uncertain and relies, to a considerable extent, on assumptions regarding current and future economics and market conditions and the availability of capital. If, in future periods, there are changes in the estimates or assumptions incorporated into the impairment review analysis, the changes could result in an adjustment to the carrying amount of the long-lived assets. To the extent that impairment has occurred, the excess of the carrying amount of long-lived assets over its estimated fair value would be recognized as an impairment loss charged to net income. For the three and nine months ended September 30, 2013, and 2012, no impairment was recognized.
Revenue Recognition	'
	Revenue Recognition
	All leases are classified as operating leases and minimum rents are recognized on a straight-line basis over the non-cancellable term of the agreements. The excess of rents recognized over amounts contractually due pursuant to the underlying leases are included in deferred rent receivable. If a lease terminates prior to its stated expiration, the deferred rent receivable relating to that lease is written off as a reduction of rental revenue.
	When arrangements include multiple elements, the revenue associated with separate elements is allocated based on the relative fair values of those elements. The revenue associated with each element is then recognized as earned. Interconnection services are considered as separate earnings processes that are provided and completed on a month-to-month basis and revenue is recognized in the period that services are performed. Set-up charges and utility installation fees are initially deferred and recognized over the term of the arrangement as revenue or the expected period of performance unless management determines a separate earnings process exists related to an installation charge.
	Tenant reimbursements for real estate taxes, common area maintenance, and other recoverable costs are recognized as revenue in the period that the related expenses are incurred.
	Above-market and below-market lease intangibles that were acquired are amortized on a straight-line basis as decreases and increases, respectively, to rental revenue over the remaining non-cancellable term of the underlying leases. For the three months ended September 30, 2013, and 2012, the net effect of amortization of acquired above-market and below-market leases resulted in an increase to rental revenue of $0.2 million and $0.4 million, respectively. For the nine months ended September 30, 2013, and 2012, the net effect of amortization of acquired above-market and below-market leases resulted in an increase to rental income of $0.5 million and $1.2 million, respectively.
	A provision for uncollectible accounts is recorded if a receivable balance relating to contractual rent, rent recorded on a straight-line basis, or tenant reimbursements is considered by management to be uncollectible. At September 30, 2013, and December 31, 2012, the allowance for doubtful accounts totaled $0.3 million and $0.6 million, respectively.
Share-Based Compensation	'
	Share-Based Compensation
	We account for share-based compensation using the fair value method of accounting. The estimated fair value of the stock options granted by us is calculated based on Black-Scholes option-pricing model and is amortized on a straight-line basis over the vesting period. The fair value of restricted share-based and Operating Partnership unit compensation is based on the market value of our common stock on the date of the grant and is amortized on a straight-line basis over the vesting period.
Asset Retirement and Environmental Remediation Obligations	'
	Asset Retirement and Environmental Remediation Obligations
	We record accruals for estimated retirement and environmental remediation obligations. The obligations relate primarily to the removal of asbestos and contaminated soil during development of the properties as well as the estimated equipment removal costs upon termination of a certain lease where we are the lessee. At September 30, 2013, and December 31, 2012, the amount included in other liabilities on the condensed consolidated balance sheets was approximately $2.5 million and $2.6 million, respectively.
Income Taxes	'
	Income Taxes
	We elected to be taxed as a REIT under the Internal Revenue Code of 1986, as amended (the “Code”), commencing with our taxable year ended December 31, 2010. To qualify as a REIT, we are required to distribute at least 90% of our taxable income to our stockholders and meet various other requirements imposed by the Code relating to such matters as operating results, asset holdings, distribution levels and diversity of stock ownership. Provided we qualify for taxation as a REIT, we are generally not subject to corporate level federal income tax on the earnings distributed currently to our stockholders. If we fail to qualify as a REIT in any taxable year, and are unable to avail ourselves of certain savings provisions set forth in the Code, all of our taxable income would be subject to federal income tax at regular corporate rates, including any applicable alternative minimum tax.
	To maintain REIT status, we must distribute a minimum of 90% of our taxable income. However, it is our policy and intent, subject to change, to distribute 100% of our taxable income and therefore no provision is required in the accompanying financial statements for federal income taxes with regards to activities of the REIT and its subsidiary pass-through entities. Any taxable income prior to the completion of the IPO is the responsibility of the Company’s prior member. The allocable share of income is included in the income tax returns of the members. The Company is subject to the statutory requirements of the locations in which it conducts business. State and local income taxes are accrued as deemed required in the best judgment of management based on analysis and interpretation of respective tax laws.
	We have elected to treat certain subsidiaries as taxable REIT subsidiaries (“TRS”). Certain activities that we undertake must be conducted by a TRS, such as services for our tenants that could be considered otherwise impermissible for us to perform and holding assets that we cannot hold directly. A TRS is subject to corporate level federal and state income taxes. Relative deferred tax assets and liabilities arising from temporary differences in financial reporting versus tax reporting are also established as determined by management.
	Deferred income taxes are recognized in certain taxable entities. Deferred income tax is generally a function of the period’s temporary differences (items that are treated differently for tax purposes than for financial reporting purposes), the utilization of tax net operating losses generated in prior years that previously had been recognized as deferred income tax assets and the reversal of any previously recorded deferred income tax liabilities. A valuation allowance for deferred income tax assets is provided if we believe all or some portion of the deferred income tax asset may not be realized. Any increase or decrease in the valuation allowance resulting from a change in circumstances that causes a change in the estimated realizability of the related deferred income tax asset is included in deferred tax expense. As of September 30, 2013, the deferred income taxes were not material.
	We currently have no liabilities for uncertain tax positions. The earliest tax year for which we are subject to examination is 2010.
Concentration of Credit Risks	'
	Concentration of Credit Risks
	Our cash and cash equivalents are maintained in various financial institutions, which, at times, may exceed federally insured limits. We have not experienced any losses in such accounts, and management believes that we are not exposed to any significant credit risk in this area. We have no off-balance sheet concentrations of credit risk, such as foreign exchange contracts, option contracts, or foreign currency hedging arrangements.
Segment Information	'
	Segment Information
	We manage our business as one reportable segment consisting of investments in data centers located in the United States. Although we provide services in several markets, these operations have been aggregated into one reportable segment based on the similar economic characteristics amongst all markets, including the nature of the services provided and the type of customers purchasing these services.

Summary_of_Significant_Account2

Summary of Significant Accounting Policies (Tables)	9 Months Ended
	Sep. 30, 2013
Summary of Significant Accounting Policies	'
Schedule of useful lives of real estate investment assets	'
	Buildings	27 to 40 years
	Building improvements	1 to 15 years
	Leasehold improvements	The shorter of the lease term or useful life of the asset

Investment_in_Real_Estate_Tabl

Investment in Real Estate (Tables)	9 Months Ended
	Sep. 30, 2013
Investment in Real Estate	'
Summary of properties owned and leased	'
	The following is a summary of the properties owned and leased at September 30, 2013 (in thousands):
	Property Name	Location	Land		Buildings and		Leasehold		Construction		Total Cost
					Improvements		Improvements		in Progress
	SV1	San Jose, CA	$	6,863	$	114,425	$	—	$	4,607	$	125,895
	SV2	Milpitas, CA	5,086		23,780		—		271		29,137
	SV3	Santa Clara, CA	3,972		45,821		—		130		49,923
	SV4	Santa Clara, CA	4,442		85,671		—		942		91,055
	SV5	Santa Clara, CA	—		—		—		21,178		21,178
	Santa Clara Campus(1)	Santa Clara, CA	8,173		8,221		—		9,055		25,449
	BO1	Somerville, MA	6,100		77,388		—		2,900		86,388
	NY1	New York, NY	—		—		32,522		180		32,702
	NY2	Secaucus, NJ	—		—		—		78,563		78,563
	VA1	Reston, VA	6,903		105,658		—		3,487		116,048
	VA2	Reston, VA	—		—		—		22,227		22,227
	DC1	Washington, DC	—		—		7,264		262		7,526
	CH1	Chicago, IL	5,493		75,951		—		5,415		86,859
	LA1	Los Angeles, CA	—		—		51,830		2,363		54,193
	LA2	Los Angeles, CA	28,467		121,819		—		5,486		155,772
	MI1	Miami, FL	728		9,846		—		118		10,692
	DE1	Denver, CO	—		—		711		15		726
	DE2	Denver, CO	—		—		669		1		670
	Total		$	76,227	$	668,580	$	92,996	$	157,200	$	995,003
	(1)    This campus includes office and light-industrial real estate buildings and land held for development in Santa Clara, CA.

Other_Assets_Tables

Other Assets (Tables)	9 Months Ended
	Sep. 30, 2013
Other Assets	'
Schedule of other assets	'
	Our other assets consisted of the following, net of amortization and depreciation, if applicable, as of September 30, 2013, and December 31, 2012 (in thousands):
		September 30,		December 31,
		2013		2012
	Deferred leasing costs	$	13,012	$	12,444
	Deferred rent receivable	16,677		15,017
	Deferred financing costs	3,758		2,520
	Corporate furniture, fixtures and equipment	4,689		4,152
	Other	9,447		8,449
	Total	$	47,583	$	42,582

Debt_Tables

Debt (Tables)	9 Months Ended
	Sep. 30, 2013
Debt	'
Summary of outstanding indebtedness	'
	A summary of outstanding indebtedness as of September 30, 2013, and December 31, 2012 is as follows (in thousands):
				Maturity	September 30,		December 31,
		Interest Rate		Date	2013		2012
	SV1 - Mortgage loan	3.69% and 3.71% at September 30, 2013, and December 31, 2012, respectively		October 9, 2014	$	58,625	$	59,750
	Revolving credit facility	2.18% and 2.46% at September 30, 2013, and December 31, 2012, respectively		January 3, 2017	108,000		—
	Total principal outstanding				$	166,625	$	59,750
Summary of amount of the entity's outstanding debt when such debt currently become due	'
	The following table summarizes the amount of our outstanding debt when such debt currently becomes due (in thousands):
	Year Ending December 31,
	Remainder of 2013	$	375
	2014	58,250
	2015	—
	2016	—
	2017	108,000
	Total	$	166,625

Stockholders_Equity_Tables

Stockholders' Equity (Tables)	9 Months Ended
	Sep. 30, 2013
Stockholders' Equity	'
Schedule of dividends declared per share on Series A Cumulative Preferred Stock and common shares	'
	Declaration Date	Record Date	Payment Date	Preferred Stock			Common Shares
	March 5, 2013	March 28, 2013	April 15, 2013	$	0.62	-1	$	0.27
	May 24, 2013	June 28, 2013	July 15, 2013	0.4531		-2	0.27
	August 30, 2013	September 30, 2013	October 15, 2013	0.4531		-3	0.27
				$	1.5262		$	0.81
	(1) Dividend covers the period from the issuance of our Series A Cumulative Preferred Stock, December 12, 2012, to April 14, 2013.
	(2) Dividend covers the period from April 15, 2013, to July 14, 2013.
	(3) Dividend covers the period from July 15, 2013, to October 14, 2013.

Noncontrolling_Interests_Opera1

Noncontrolling Interests - Operating Partnership (Tables)	9 Months Ended
	Sep. 30, 2013
Noncontrolling Interests - Operating Partnership	'
Schedule of ownership interest in the Operating Partnership	'
		September 30, 2013			December 31, 2012
		Number of Units	Percentage of Total		Number of Units	Percentage of Total
	The Company	20,872,386	45.1	%	20,610,523	44.8	%
	Noncontrolling interests consist of:
	Common units held by third parties	25,275,390	54.7	%	25,275,390	55	%
	Incentive units held by employees	85,457	0.2	%	78,319	0.2	%
	Total	46,233,233	100	%	45,964,232	100	%

Equity_Incentive_Plan_Tables

Equity Incentive Plan (Tables)	9 Months Ended
	Sep. 30, 2013
Equity Incentive Plan	'
Schedule of stock option activity	'
		Number of		Weighted
		Shares Subject		Average
		to Option		Exercise Price
	Options outstanding, December 31, 2012	1,017,195		$	17.25
	Granted	209,268		32.5
	Forfeited	(23,865	)	21.22
	Exercised	(40,277	)	15.65
	Options outstanding, September 30, 2013	1,162,321		$	19.97
Schedule of unvested shares subject to option	'
		Number of		Weighted
		Shares Subject		Average Fair
		to Option		Value at Grant
	Unvested balance, December 31, 2012	730,159		$	5.7
	Granted	209,268		10.01
	Forfeited	(23,865	)	6.69
	Vested	(261,862	)	5.55
	Unvested balance, September 30, 2013	653,700		$	7.11
Schedule of restricted awards	'
		Restricted		Weighted
		Awards		Average Fair
				Value at Grant
	Unvested balance, December 31, 2012	598,695		$	21.37
	Granted	192,514		32.47
	Forfeited	(16,902	)	25.08
	Vested	(229,613	)	20.8
	Unvested balance, September 30, 2013	544,694		$	25.42

Earnings_Per_Share_Tables

Earnings Per Share (Tables)	9 Months Ended
	Sep. 30, 2013
Earnings Per Share	'
Summary of basic and diluted income per share	'
	The following is a summary of basic and diluted income per share (in thousands, except share and per share amounts):
		Three Months Ended September 30,				Nine Months Ended September 30,
		2013		2012		2013		2012
	Net income attributable to common shares	$	2,901	$	1,320	$	7,368	$	2,749
	Weighted average common shares outstanding - basic	20,871,504		20,554,893		20,793,596		20,514,713
	Effect of potentially dilutive common shares:
	Stock options	391,398		267,831		388,889		225,520
	Unvested restricted awards	217,069		204,911		283,225		150,661
	Weighted average common shares outstanding - diluted	21,479,971		21,027,635		21,465,710		20,890,894
	Net income per share attributable to common shares
	Basic	$	0.14	$	0.06	$	0.35	$	0.13
	Diluted	$	0.14	$	0.06	$	0.34	$	0.13

Commitments_and_Contingencies_

Commitments and Contingencies (Tables)	9 Months Ended
	Sep. 30, 2013
Commitments and Contingencies	'
Summary of contractual obligations	'
	The following table summarizes our contractual obligations as of September 30, 2013 (in thousands):
		Remainder of
	Obligation	2013		2014		2015		2016		2017		Thereafter		Total
	Operating leases	$	4,644	$	18,902	$	19,258	$	18,942	$	17,503	$	80,893	$	160,142
	Credit Facility(1)	588		2,353		2,353		2,353		108,000		—		115,647
	Mortgages payable (2)	913		59,843		—		—		—		—		60,756
	Construction Contracts (3)	75,808		429		—		—		—		—		76,237
	Other (4)	1,441		1,536		1,071		564		176		1,484		6,272
	Total	$	83,394	$	83,063	$	22,682	$	21,859	$	125,679	$	82,377	$	419,054
	(1) Includes $108.0 million outstanding and estimated annual interest payments assuming no draws or payments on the revolving credit facility through the maturity date of January 3, 2017. The revolving credit facility is subject to variable rates and we estimated interest payments based on the interest rate as of September 30, 2013.
	(2) Includes $58.6 million of mortgage principal payments and estimated interest payments until debt maturity on October 9, 2014. We estimated interest payments of $0.5 million for the remainder of 2013 and $1.6 million in 2014. The mortgage payable is subject to variable rates and we estimated interest payments based on the interest rate as of September 30, 2013.
	(3) Obligations for construction contracts for properties under construction, tenant related capital expenditures, and other capital improvements.
	(4) Obligations for power contracts, telecommunications leases, and internal system development.

Organization_and_Description_o1

Organization and Description of Business (Details)	Sep. 30, 2013
	item
Organization	'
Number of operating data center facilities	14
Common Shares | Operating partnership	'
Organization	'
Percentage of ownership interests held by the entity	45.10%

Summary_of_Significant_Account3

Summary of Significant Accounting Policies (Details) (USD $)	3 Months Ended		9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Investments in Real Estate	'	'	'	'
Capitalized interest costs	$1.10	$0.30	$3	$1.50
Depreciation expense	$13.70	$10.70	$38.90	$29.70
Buildings | Minimum	'	'	'	'
Investments in Real Estate	'	'	'	'
Useful lives	'	'	'27 years	'
Buildings | Maximum	'	'	'	'
Investments in Real Estate	'	'	'	'
Useful lives	'	'	'40 years	'
Building improvements | Minimum	'	'	'	'
Investments in Real Estate	'	'	'	'
Useful lives	'	'	'1 year	'
Building improvements | Maximum	'	'	'	'
Investments in Real Estate	'	'	'	'
Useful lives	'	'	'15 years	'

Summary_of_Significant_Account4

Summary of Significant Accounting Policies (Details 2) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Summary of Significant Accounting Policies	'	'	'	'	'
Impairment loss related to goodwill	$0	$0	$0	$0	'
Goodwill	41,191,000	'	41,191,000	'	41,191,000
Acquisition of Investment in Real Estate	'	'	'	'	'
Impairment loss related to intangible assets	0	0	0	0	'
Recoverability of Long-Lived Assets	'	'	'	'	'
Impairment of long-lived assets	$0	$0	$0	$0	'

Summary_of_Significant_Account5

Summary of Significant Accounting Policies (Details 3) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Revenue Recognition	'	'	'	'	'
Increase to rental revenue	$200,000	$400,000	$500,000	$1,200,000	'
Allowance for doubtful accounts (in dollars)	320,000	'	320,000	'	625,000
Asset Retirement and Environmental Remediation Obligations	'	'	'	'	'
Asset retirement and environmental remediation obligations	2,500,000	'	2,500,000	'	2,600,000
Income taxes	'	'	'	'	'
Minimum percentage of distribution of taxable income to qualify as REIT	'	'	90.00%	'	'
Percentage of distribution of taxable income as per company policy	'	'	100.00%	'	'
Provision for federal income taxes	'	'	0	'	'
Liabilities for uncertain positions	$0	'	$0	'	'

Summary_of_Significant_Account6

Summary of Significant Accounting Policies (Details 4)	9 Months Ended
	Sep. 30, 2013
	item
Concentration of Credit Risks	'
Number of off-balance-sheet concentrations of credit risk	0
Segment information	'
Number of reportable segments	1

Investment_in_Real_Estate_Deta

Investment in Real Estate (Details) (USD $)

9 Months Ended

9 Months Ended

0 Months Ended

9 Months Ended

Sep. 30, 2013

Dec. 31, 2012

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

Feb. 07, 2013

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

item

SV1, San Jose, CA

SV2, Milpitas, CA

SV3, Santa Clara, CA

SV4, Santa Clara, CA

SV5, Santa Clara, CA

Santa Clara Campus, Santa Clara, CA

BO1, Somerville, MA

NY1, New York, NY

NY2, Secaucus, NJ

NY2, Secaucus, NJ

VA1, Reston, VA

VA2, Reston, VA

DC1, Washington, DC

CH1, Chicago, IL

LA1, Los Angeles, CA

LA2, Los Angeles, CA

MI1, Miami, FL

DE1, Denver, CO

DE2, Denver, CO

Investment in Real Estate

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Real estate value of acquired land and a vacant building

'

'

'

'

'

'

'

'

'

'

$23,000,000

'

'

'

'

'

'

'

'

'

'

Number of other data center facilities on which development is commenced

2

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Reclassification of property

'

'

'

'

'

'

2,400,000

'

'

'

'

'

'

5,200,000

'

'

'

'

'

'

'

Land

76,227,000

85,868,000

6,863,000

5,086,000

3,972,000

4,442,000

'

8,173,000

6,100,000

'

'

'

6,903,000

'

'

5,493,000

'

28,467,000

728,000

'

'

Buildings and Improvements

668,580,000

596,405,000

114,425,000

23,780,000

45,821,000

85,671,000

'

8,221,000

77,388,000

'

'

'

105,658,000

'

'

75,951,000

'

121,819,000

9,846,000

'

'

Leasehold improvements

92,996,000

85,907,000

'

'

'

'

'

'

'

32,522,000

'

'

'

'

7,264,000

'

51,830,000

'

'

711,000

669,000

Construction in progress

157,200,000

61,328,000

4,607,000

271,000

130,000

942,000

21,178,000

9,055,000

2,900,000

180,000

'

78,563,000

3,487,000

22,227,000

262,000

5,415,000

2,363,000

5,486,000

118,000

15,000

1,000

Total investments in real estate

$995,003,000

'

$125,895,000

$29,137,000

$49,923,000

$91,055,000

$21,178,000

$25,449,000

$86,388,000

$32,702,000

'

$78,563,000

$116,048,000

$22,227,000

$7,526,000

$86,859,000

$54,193,000

$155,772,000

$10,692,000

$726,000

$670,000

Other_Assets_Details

Other Assets (Details) (USD $)	Sep. 30, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
Other Assets	'	'
Deferred leasing costs	$13,012	$12,444
Deferred rent receivable	16,677	15,017
Deferred financing costs	3,758	2,520
Corporate furniture, fixtures and equipment	4,689	4,152
Other	9,447	8,449
Total	$47,583	$42,582

Debt_Details

Debt (Details) (USD $)

Sep. 30, 2013

Dec. 31, 2012

Sep. 30, 2013

Dec. 31, 2012

Sep. 30, 2013

Jun. 28, 2013

Dec. 31, 2012

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

Jun. 28, 2013

Jan. 02, 2013

Sep. 30, 2013

SV1 - Mortgage loan

SV1 - Mortgage loan

Revolving credit facility

Revolving credit facility

Revolving credit facility

Revolving credit facility

Revolving credit facility

Revolving credit facility

Revolving credit facility

Revolving credit facility

Revolving credit facility

Revolving credit facility

Revolving credit facility

Revolving credit facility

Prior facility

Prior facility

Prior facility

item

Operating partnership

Minimum

Maximum

LIBOR

LIBOR

LIBOR

Base rate

Base rate

Base rate

Operating partnership

Operating partnership

Minimum

Maximum

Operating partnership

Minimum

Maximum

Operating partnership

Operating partnership

Operating partnership

Operating partnership

Debt

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Interest rate as of reporting date (as a percent)

'

'

3.69%

3.71%

2.18%

'

2.46%

'

'

'

'

'

'

'

'

'

'

'

'

Total principal outstanding

$166,625,000

$59,750,000

$58,625,000

$59,750,000

$108,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Commitment under the credit agreement

'

'

'

'

405,000,000

355,000,000

'

500,000,000

'

'

'

'

'

'

'

'

355,000,000

225,000,000

'

Number of options available for extensions

'

'

'

'

1

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Extension fee (as a percent)

'

'

'

'

0.25%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Total increase in commitment under accordion feature

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

50,000,000

'

145,000,000

Reference rate

'

'

'

'

'

'

'

'

'

'

'LIBOR

'

'

'base rate

'

'

'

'

'

Interest rate margin (as a percent)

'

'

'

'

'

'

'

'

'

'

'

2.00%

2.75%

'

1.00%

1.75%

'

'

'

Amount available for borrowing under the facility

'

'

'

'

396,600,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Outstanding borrowings

'

'

'

'

108,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Leverage ratio, Covenant (as a percent)

'

'

'

'

'

'

'

'

'

60.00%

'

'

'

'

'

'

'

'

'

Leverage ratio (as a percent)

'

'

'

'

11.50%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Secured debt ratio, Covenant (as a percent)

'

'

'

'

'

'

'

'

'

3.80%

'

'

'

'

'

'

'

'

'

Secured debt ratio (as a percent)

'

'

'

'

4.00%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Fixed charge coverage ratio, Covenant

'

'

'

'

'

'

'

'

1.75

'

'

'

'

'

'

'

'

'

'

Fixed charge coverage ratio

'

'

'

'

'

'

'

'

750.00%

100.00%

'

'

'

'

'

'

'

'

'

Unhedged variable rate debt ratio, Covenant (as a percent)

'

'

'

'

'

'

'

'

'

30.00%

'

'

'

'

'

'

'

'

'

Unhedged variable rate debt ratio (as a percent)

'

'

'

'

10.80%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Repayment of senior mortgage loan

'

'

$58,600,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Debt_Details_2

Debt (Details 2) (USD $)	Sep. 30, 2013
In Thousands, unless otherwise specified
Debt maturities	'
Remainder of 2013	$375
2014	58,250
2017	108,000
Total	$166,625

Stockholders_Equity_Details

Stockholders' Equity (Details) (USD $)	Sep. 30, 2013	Aug. 30, 2013	24-May-13	Mar. 05, 2013
Preferred Stock	'	'	'	'
Stockholders' Equity	'	'	'	'
Dividend declared (in dollars per share)	$1.53	$0.45	$0.45	$0.62
Common Stock	'	'	'	'
Stockholders' Equity	'	'	'	'
Dividend declared (in dollars per share)	$0.81	$0.27	$0.27	$0.27

Noncontrolling_Interests_Opera2

Noncontrolling Interests - Operating Partnership (Details) (USD $)	0 Months Ended	3 Months Ended			9 Months Ended
In Millions, except Share data, unless otherwise specified	Dec. 12, 2012	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Sep. 30, 2013	Dec. 31, 2012
Noncontrolling Interests - Operating Partnership	'	'	'	'	'	'
Conversion ratio for common operating partnership units	'	'	'	'	1	'
Noncontrolling Interests Operating Partnership	'	'	'	'	'	'
Number of Units (in shares)	'	46,233,233	'	'	46,233,233	45,964,232
Percentage of Total	'	100.00%	'	'	100.00%	100.00%
Shares of common stock issued related to employee compensation arrangements	'	'	'	'	262,665	'
Quarterly distributions received by holders of operating partnership units (in dollars per unit)	'	$0.27	$0.27	$0.27	'	'
Preferred Operating Partnership units issued to CoreSite Realty Corporation (in shares)	4,600,000	'	'	'	'	'
Redemption value of the noncontrolling interests	'	$860.70	'	'	$860.70	'
Closing price of the Company's stock (in dollars per share)	'	$33.94	'	'	$33.94	'
The Company	'	'	'	'	'	'
Noncontrolling Interests Operating Partnership	'	'	'	'	'	'
Number of Units (in shares)	'	20,872,386	'	'	20,872,386	20,610,523
Percentage of Total	'	45.10%	'	'	45.10%	44.80%
Common units held by third parties	'	'	'	'	'	'
Noncontrolling Interests Operating Partnership	'	'	'	'	'	'
Number of Units (in shares)	'	25,275,390	'	'	25,275,390	25,275,390
Percentage of Total	'	54.70%	'	'	54.70%	55.00%
Incentive units held by employees	'	'	'	'	'	'
Noncontrolling Interests Operating Partnership	'	'	'	'	'	'
Number of Units (in shares)	'	85,457	'	'	85,457	78,319
Percentage of Total	'	0.20%	'	'	0.20%	0.20%

Equity_Incentive_Plan_Details

Equity Incentive Plan (Details) (USD $)	0 Months Ended	9 Months Ended
In Millions, except Share data, unless otherwise specified	22-May-13	Sep. 30, 2013
Stock options	'	'
Equity Incentive Plan	'	'
Increase in number of shares of common stock authorized for issuance	3,000,000	'
Shares of common stock that were available for issuance pursuant to the 2010 Plan	6,000,000	3,632,820
Number of Shares Subject to Option	'	'
Options outstanding at the beginning of the period (in shares)	'	1,017,195
Granted (in shares)	'	209,268
Forfeited (in shares)	'	-23,865
Exercised (in shares)	'	-40,277
Options outstanding at the end of the period (in shares)	'	1,162,321
Weighted Average Exercise Price	'	'
Options outstanding at the beginning of the period (in dollars per share)	'	$17.25
Granted (in dollars per share)	'	$32.50
Forfeited (in dollars per share)	'	$21.22
Exercised (in dollars per share)	'	$15.65
Options outstanding at the end of the period (in dollars per share)	'	$19.97
Number of Shares Subject to Option	'	'
Unvested balance at the beginning of the period (in shares)	'	730,159
Granted (in shares)	'	209,268
Forfeited (in shares)	'	-23,865
Vested (in shares)	'	-261,862
Unvested balance at the end of the period (in shares)	'	653,700
Weighted Average Fair Value at Grant	'	'
Unvested balance at the beginning of the period (in dollars per share)	'	$5.70
Granted (in dollars per share)	'	$10.01
Forfeited (in dollars per share)	'	$6.69
Vested (in dollars per share)	'	$5.55
Unvested balance at the end of the period (in dollars per share)	'	$7.11
Compensation cost not yet recognized	'	'
Unearned compensation	'	$3.90
Stock options | Weighted average	'	'
Compensation cost not yet recognized	'	'
Vesting period	'	'2 years 2 months 12 days
Restricted Awards	'	'
Restricted Awards	'	'
Unvested balance at the beginning of the period (in shares)	'	598,695
Granted (in shares)	'	192,514
Forfeited (in shares)	'	-16,902
Vested (in shares)	'	-229,613
Unvested balance at the end of the period (in shares)	'	544,694
Weighted Average Fair Value at Grant Date	'	'
Unvested balance at the beginning of the period (in dollars per share)	'	$21.37
Granted (in dollars per share)	'	$32.47
Forfeited (in dollars per share)	'	$25.08
Vested (in dollars per share)	'	$20.80
Unvested balance at the end of the period (in dollars per share)	'	$25.42
Compensation cost not yet recognized	'	'
Unearned compensation	'	$11.30
Restricted Awards | Weighted average	'	'
Compensation cost not yet recognized	'	'
Vesting period	'	'2 years 4 months 24 days
Restricted awards	'	'
Restricted Awards	'	'
Granted (in shares)	'	187,186
RSUs	'	'
Restricted Awards	'	'
Granted (in shares)	'	5,328
Compensation cost not yet recognized	'	'
Holder of RSU becomes entitled to the number of shares of common stock for each RSU on applicable vesting date	'	1

Earnings_Per_Share_Details

Earnings Per Share (Details) (USD $)	3 Months Ended		9 Months Ended
In Thousands, except Share data, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Earnings Per Share	'	'	'	'
Net income attributable to common shares	$2,901	$1,320	$7,368	$2,749
Weighted average common shares outstanding - basic	20,871,504	20,554,893	20,793,596	20,514,713
Effect of potentially dilutive common shares:	'	'	'	'
Stock options	391,398	267,831	388,889	225,520
Unvested restricted awards	217,069	204,911	283,225	150,661
Weighted average common shares outstanding - diluted	21,479,971	21,027,635	21,465,710	20,890,894
Net income per share attributable to common shares	'	'	'	'
Basic (in dollars per share)	$0.14	$0.06	$0.35	$0.13
Diluted (in dollars per share)	$0.14	$0.06	$0.34	$0.13
Earnings Per Share	'	'	'	'
Weighted average potentially dilutive securities excluded in calculation of basic and diluted income (loss) per share	211,721	200,908	166,732	100,587

Estimated_Fair_Value_of_Financ1

Estimated Fair Value of Financial Instruments (Details) (USD $)	Sep. 30, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
Fair value of assets and liabilities measured on a recurring basis	'	'
Balance of mortgage loan payable and revolving credit facility	$58,625	$59,750
Significant Unobservable Inputs (Level 3)	'	'
Fair value of assets and liabilities measured on a recurring basis	'	'
Balance of mortgage loan payable and revolving credit facility	$166,600	$59,800

Related_Party_Transactions_Det

Related Party Transactions (Details) (USD $)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Related Party Transactions	'	'	'	'
Rental revenue	$35,283	$31,603	$102,590	$91,837
Affiliate of the Carlyle Group | VA1- Mortgage loan	'	'	'	'
Related Party Transactions	'	'	'	'
Net rentable space leased to an affiliate (in square feet)	1,520	'	1,520	'
Common interest (as a percent)	54.70%	'	54.70%	'
Affiliate of the Carlyle Group | VA1- Mortgage loan | Maximum	'	'	'	'
Related Party Transactions	'	'	'	'
Rental revenue	$100	$100	$200	$200

Commitments_and_Contingencies_1

Commitments and Contingencies (Details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Other expenses	'	'	'	'
Rent expense	$5,082,000	$4,689,000	$14,631,000	$13,957,000
Operating leases	'	'	'	'
Remainder of 2013	4,644,000	'	4,644,000	'
2014	18,902,000	'	18,902,000	'
2015	19,258,000	'	19,258,000	'
2016	18,942,000	'	18,942,000	'
2017	17,503,000	'	17,503,000	'
Thereafter	80,893,000	'	80,893,000	'
Total	160,142,000	'	160,142,000	'
Construction Contracts	'	'	'	'
Remainder of 2013	75,808,000	'	75,808,000	'
2014	429,000	'	429,000	'
Total	76,237,000	'	76,237,000	'
Other	'	'	'	'
Remainder of 2013	1,441,000	'	1,441,000	'
2014	1,536,000	'	1,536,000	'
2015	1,071,000	'	1,071,000	'
2016	564,000	'	564,000	'
2017	176,000	'	176,000	'
Thereafter	1,484,000	'	1,484,000	'
Total	6,272,000	'	6,272,000	'
Total	'	'	'	'
Remainder of 2013	83,394,000	'	83,394,000	'
2014	83,063,000	'	83,063,000	'
2015	22,682,000	'	22,682,000	'
2016	21,859,000	'	21,859,000	'
2017	125,679,000	'	125,679,000	'
Thereafter	82,377,000	'	82,377,000	'
Total	419,054,000	'	419,054,000	'
Contractual obligations	'	'	'	'
Remainder of 2013	375,000	'	375,000	'
2014	58,250,000	'	58,250,000	'
2017	108,000,000	'	108,000,000	'
Total	166,625,000	'	166,625,000	'
Credit Facility	'	'	'	'
Contractual obligations	'	'	'	'
Remainder of 2013	588,000	'	588,000	'
2014	2,353,000	'	2,353,000	'
2015	2,353,000	'	2,353,000	'
2016	2,353,000	'	2,353,000	'
2017	108,000,000	'	108,000,000	'
Total	115,647,000	'	115,647,000	'
Mortgages payable	'	'	'	'
Contractual obligations	'	'	'	'
Remainder of 2013	913,000	'	913,000	'
2014	59,843,000	'	59,843,000	'
Total	60,756,000	'	60,756,000	'
Principal payments	58,600,000	'	58,600,000	'
Estimated interest payments in 2013	'	'	500,000	'
Estimated interest payments in 2014	'	'	$1,600,000	'