CoreSite Realty 10-Q 26 Apr 19 2019 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2019	Apr. 24, 2019
Document and Entity Information
Entity Registrant Name	CoreSite Realty Corp
Entity Central Index Key	0001490892
Document Type	10-Q
Document Period End Date	Mar. 31, 2019
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Common Stock, Shares Outstanding		36,898,253
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q1

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Investments in real estate:
Land	$ 86,955	$ 86,955
Buildings and improvements	1,737,967	1,730,329
Total investments in real estate	1,824,922	1,817,284
Less: Accumulated depreciation and amortization	(621,682)	(590,784)
Net investment in operating properties	1,203,240	1,226,500
Construction in progress	364,458	265,921
Net investments in real estate	1,567,698	1,492,421
Operating lease right-of-use assets	186,311	190,304
Cash and cash equivalents	2,294	2,599
Accounts and other receivables, net of allowance for doubtful accounts of $283 and $417 as of March 31, 2019, and December 31, 2018, respectively	26,148	18,464
Lease intangibles, net of accumulated amortization of $8,375 and $7,756 as of March 31, 2019, and December 31, 2018, respectively	6,324	6,943
Goodwill	40,646	40,646
Other assets, net	103,441	102,290
Total assets	1,932,862	1,853,667
Liabilities:
Debt, net of unamortized deferred financing costs of $5,284 and $5,677 as of March 31, 2019, and December 31, 2018, respectively	1,210,716	1,130,823
Operating lease liabilities	199,112	202,699
Accounts payable and accrued expenses	116,195	89,315
Accrued dividends and distributions	55,109	55,679
Acquired below-market lease contracts, net of accumulated amortization of $3,948 and $3,840 as of March 31, 2019, and December 31, 2018, respectively	2,737	2,846
Unearned revenue, prepaid rent and other liabilities	42,823	37,672
Total liabilities	1,626,692	1,519,034
Stockholders' equity:
Common Stock, par value $0.01, 100,000,000 shares authorized and 36,901,8291 and 36,708,691 shares issued and outstanding at March 31, 2019, and December 31, 2018, respectively	364	363
Additional paid-in capital	494,923	491,314
Accumulated other comprehensive income (loss)	(5,733)	(2,193)
Distributions in excess of net income	(267,849)	(246,929)
Total stockholders' equity	221,705	242,555
Noncontrolling interests	84,465	92,078
Total equity	306,170	334,633
Total liabilities and equity	$ 1,932,862	$ 1,853,667

CONSOLIDATED BALANCE SHEETS (Pa

CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
CONDENSED CONSOLIDATED BALANCE SHEETS
Allowance for doubtful accounts (in dollars)	$ 283	$ 417
Accumulated amortization, lease intangibles (in dollars)	8,375	7,756
Unamortized Debt Issuance Expense	5,284	5,677
Accumulated amortization of below-market lease	$ 3,948	$ 3,840
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	36,901,829	36,708,691
Common Stock, shares outstanding	36,901,829	36,708,691

CONSOLIDATED STATEMENTS OF OPER

CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Data center revenue:
Total operating revenues	$ 138,895	$ 129,619
Operating expenses:
Property operating and maintenance	38,110	33,848
Real estate taxes and insurance	6,196	4,937
Depreciation and amortization	35,646	33,776
Sales and marketing	5,652	5,080
General and administrative	10,170	9,185
Rent	7,688	6,400
Transaction costs		56
Total operating expenses	103,462	93,282
Operating income	35,433	36,337
Interest expense	(9,498)	(7,738)
Income before income taxes	25,935	28,599
Income tax expense	(30)	(33)
Net income	25,905	28,566
Net income attributable to noncontrolling interests	6,244	8,264
Net income attributable to common shares	$ 19,661	$ 20,302
Net income per share attributable to common shares:
Basic (in dollars per share)	$ 0.54	$ 0.60
Diluted (in dollars per share)	$ 0.54	$ 0.59
Weighted average common shares outstanding
Basic (in shares)	36,347,781	33,935,564
Diluted (in shares)	36,547,065	34,164,235
Rental Power And Related Revenue
Data center revenue:
Revenue	$ 117,853	$ 110,008
Interconnection Revenue
Data center revenue:
Revenue	18,416	16,560
Office Light Industrial And Other Revenue
Data center revenue:
Revenue	$ 2,626	$ 3,051

CONSOLIDATED STATEMENTS OF COMP

CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME
Net income	$ 25,905	$ 28,566
Other comprehensive income (loss):
Unrealized gain (loss) on derivative contracts	(4,466)	609
Reclassification of other comprehensive income (loss) to interest expense	(198)	(32)
Comprehensive income	21,241	29,143
Comprehensive income attributable to noncontrolling interests	5,120	8,431
Comprehensive income attributable to CoreSite Realty Corporation	$ 16,121	$ 20,712

CONSOLIDATED STATEMENTS OF EQUI

CONSOLIDATED STATEMENTS OF EQUITY - USD ($) $ in Thousands	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income (Loss)	Distributions in Excess of Net Income	Total Stockholders' Equity	Noncontrolling Interests	Total
Balance at Dec. 31, 2017	$ 338	$ 457,495	$ 753	$ (177,566)	$ 281,020	$ 137,624	$ 418,644
Balance (in shares) at Dec. 31, 2017	34,240,815
Increase (Decrease) in Stockholders' Equity
Redemption of noncontrolling interests		70			70	(70)
Redemption of noncontrolling interests (in shares)	7,056
Issuance of stock awards, net of forfeitures (in shares)	201,181
Exercise of stock options		100			100		100
Exercise of stock options (in shares)	5,161
Share-based compensation	$ 2	2,739			2,741		2,741
Dividends and distributions				(33,749)	(33,749)	(13,553)	(47,302)
Net income				20,302	20,302	8,264	28,566
Other comprehensive income			410		410	167	577
Balance at Mar. 31, 2018	$ 340	460,404	1,163	(191,013)	270,894	132,432	403,326
Balance (in shares) at Mar. 31, 2018	34,454,213
Balance at Dec. 31, 2018	$ 363	491,314	(2,193)	(246,929)	242,555	92,078	334,633
Balance (in shares) at Dec. 31, 2018	36,708,691
Increase (Decrease) in Stockholders' Equity
Issuance of stock awards, net of forfeitures (in shares)	192,009
Exercise of stock options		17			17		17
Exercise of stock options (in shares)	1,129
Share-based compensation	$ 1	3,592			3,593		3,593
Dividends and distributions				(40,581)	(40,581)	(12,733)	(53,314)
Net income				19,661	19,661	6,244	25,905
Other comprehensive income			(3,540)		(3,540)	(1,124)	(4,664)
Balance at Mar. 31, 2019	$ 364	$ 494,923	$ (5,733)	$ (267,849)	$ 221,705	$ 84,465	$ 306,170
Balance (in shares) at Mar. 31, 2019	36,901,829

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
CASH FLOWS FROM OPERATING ACTIVITIES
Net income	$ 25,905	$ 28,566
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	35,646	33,776
Amortization of above/below market leases	(86)	(175)
Amortization of deferred financing costs	611	566
Share-based compensation	3,432	2,626
Bad debt expense	(27)	(145)
Changes in operating assets and liabilities:
Accounts receivable	(7,658)	3,942
Deferred rent receivable	1,036	(1,250)
Deferred leasing costs	(2,694)	(3,405)
Other assets	(4,519)	(4,709)
Accounts payable and accrued expenses	2,757	(1,956)
Unearned revenue, prepaid rent and other liabilities	857	1,911
Operating leases	643	(1,400)
Net cash provided by operating activities	55,903	58,347
CASH FLOWS FROM INVESTING ACTIVITIES
Tenant improvements	(1,046)	(1,295)
Real estate improvements	(80,795)	(54,338)
Business combinations and asset acquisitions		(4,383)
Net cash used in investing activities	(81,841)	(60,016)
CASH FLOWS FROM FINANCING ACTIVITIES
Proceeds from exercise of stock options	17	100
Proceeds from revolving credit facility	88,000	67,000
Payments on revolving credit facility	(8,500)	(20,000)
Dividends and distributions	(53,884)	(47,599)
Net cash provided by (used in) financing activities	25,633	(499)
Net change in cash and cash equivalents	(305)	(2,168)
Cash and cash equivalents, beginning of year	2,599	5,247
Cash and cash equivalents, end of year	2,294	3,079
SUPPLEMENTAL DISCLOSURE OF CASH FLOW INFORMATION
Cash paid for interest, net of capitalized amounts	6,350	4,354
Cash paid for operating lease liabilities	6,071	6,795
NON-CASH INVESTING AND FINANCING ACTIVITY
Construction costs payable capitalized to real estate	66,123	22,061
Accrual of dividends and distributions	$ 55,109	$ 48,678

Organization and Description of

Organization and Description of Business	3 Months Ended
	Mar. 31, 2019
Organization and Description of Business
Organization and Description of Business	1. Organization and Description of Business CoreSite Realty Corporation (the “Company,” “we,” “us,” or “our”) was organized in the State of Maryland on February 17, 2010, and is a fully-integrated, self-administered, and self-managed real estate investment trust (“REIT”). Through our controlling interest in CoreSite, L.P. (our “Operating Partnership”), we are engaged in the business of owning, acquiring, constructing and operating data centers. As of March 31, 2019, the Company owns a 75.9% common interest in our Operating Partnership, and affiliates of The Carlyle Group and others own a 24.1% interest in our Operating Partnership. See additional discussion in Note 10, Noncontrolling Interests — Operating Partnership.

Summary of Significant Accounti

Summary of Significant Accounting Policies	3 Months Ended
	Mar. 31, 2019
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 U.S. Securities and Exchange Commission. Accordingly, these unaudited 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 three months ended March 31, 2019, are not necessarily indicative of the expected results for the year ending December 31, 2019. These unaudited 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, 2018. Our Operating Partnership meets the definition and criteria of a variable interest entity (“VIE”) and we are the primary beneficiary of the VIE. Our sole significant asset is the investment in our Operating Partnership, and consequently, substantially all of our assets and liabilities represent those assets and liabilities of our Operating Partnership. Our debt is an obligation of our Operating Partnership where the creditors also have recourse against the credit of the Company. Intercompany balances and transactions have been eliminated upon consolidation. Recent Accounting Pronouncements Not Yet Adopted Fair Value Measurement In August 2018, the Financial Accounting Standards Board (“FASB”) issued guidance codified in Accounting Standards Update (“ASU”) 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework – Changes to the Disclosure Requirements for Fair Value Measurement. ASU 2018-13 improves the overall usefulness of disclosures to financial statement users and reduces unnecessary costs in preparing fair value measurement disclosures. The standard will be effective for interim and annual reporting periods beginning after December 15, 2019, with early adoption permitted. We do not expect the provisions of ASU 2018-13 to have a material impact on our condensed consolidated financial statements. Intangibles – Goodwill and Other – Internal-Use Software In August 2018, the FASB issued guidance codified in ASU 2018-15, Intangibles – Goodwill and Other – Internal-Use Software (Subtopic 350-40): Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract. ASU 2018-15 clarifies that implementation costs incurred by customers in cloud computing arrangements are deferred if they would be capitalized by customers in software licensing arrangements under the internal-use software guidance. Additionally, ASU 2018-15 clarifies that all capitalized costs must be presented in the same financial statement line item as the cloud computing arrangement. The standard will be effective, on either a prospective or retrospective basis, for interim and annual reporting periods beginning after December 15, 2019, with early adoption permitted. We are currently evaluating the provisions of ASU 2018-15 and whether the provisions will have a material impact on our condensed consolidated financial statements. We determined that all other recently issued accounting pronouncements will not have a material impact on our consolidated financial statements or do not apply to our operations. Use of Estimates The preparation of these unaudited 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 unaudited 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 our standalone selling prices, performance-based equity compensation plans and the carrying values of our real estate properties, goodwill, and accrued liabilities. 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. 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 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, rent expense and internal costs of personnel performing development, if such costs are incremental and identifiable to a specific development project. Capitalization of costs begins upon commencement of development efforts and ceases when the project 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 $2.6 million and $1.1 million for the three months ended March 31, 2019, and 2018, 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 10 years Leasehold improvements The shorter of the lease term or useful life of the asset Depreciation expense was $32.2 million and $29.1 million for the three months ended March 31, 2019, and 2018, respectively. Acquisition of Investment in Real Estate When accounting for business combinations and asset acquisitions, the fair value of the real estate acquired is allocated to the acquired tangible assets, consisting primarily of land, building and building 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 primary difference between business combinations and asset acquisitions is that asset acquisitions require cost accumulation and allocation at a relative fair value. Acquisition costs are capitalized for asset acquisitions and expensed for business combinations. 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 market lease rates for the corresponding in-place leases, measured over a period equal to the remaining noncancelable term of the lease and, for below-market leases, over a time 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 revenue, 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. 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 related to these intangible assets was recognized for the three months ended March 31, 2019, or 2018. 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 March 31, 2019, and December 31, 2018, we had $40.6 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 months ended March 31, 2019, or 2018. 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. Initial Direct Costs Initial direct costs include commissions paid to third parties, including brokers, leasing and referral agents, and internal sales commissions paid to employees for successful execution of lease agreements. Initial direct costs are incremental costs that would not have been incurred if the lease agreement had not been executed. These initial direct costs are capitalized and generally amortized over the term of the related leases using the straight-line method. If a customer lease terminates prior to the expiration of its initial term, any unamortized initial direct costs related to the lease are written off to amortization expense. Amortization of initial direct costs were $3.4 million and $3.9 million for the three months ended March 31, 2019, and 2018, respectively. Initial direct costs are included within other assets in the condensed consolidated balance sheets and consisted of the following, net of amortization, as of March 31, 2019, and December 31, 2018 (in thousands): March 31, December 31, 2019 2018 Internal sales commissions $ 13,732 $ 14,199 Third party commissions 9,594 9,855 Other 549 597 Total $ 23,875 $ 24,651 Deferred Financing Costs 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 indebtedness and the amortization is included as a component of interest expense. Depending on the type of debt instrument, deferred financing costs are reported either in other assets or as a direct deduction from the carrying amount of the related debt liabilities in our condensed consolidated balance sheets. Recoverability of Long-Lived Assets We review our 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 months ended March 31, 2019, and 2018, no impairment of long-lived assets was recognized in the condensed consolidated financial statements. Derivative Instruments and Hedging Activities We reflect all derivative instruments at fair value as either assets or liabilities on the condensed consolidated balance sheets. For those derivative instruments that are designated and qualify as hedging instruments, we record the gain or loss on the hedging instruments as a component of accumulated other comprehensive income or loss. For derivatives that do not meet the criteria for hedge accounting, changes in fair value are immediately recognized within net income. See additional discussion in Note 8, Derivatives and Hedging Activities. Internal-Use Software We recognize internal-use software development costs based on the development stage of the project and nature of the cost. Internal and external costs incurred during the preliminary project stage are expensed as they are incurred. Internal and external costs incurred to develop internal-use software during the application development stage are capitalized. Internal and external training costs and maintenance costs during the post-implementation-operation stage are expensed as incurred. Completed projects are placed into service and amortized over the estimated useful life of the software. No impairment of internal-use software was recognized in the condensed consolidated financial statements for the three months ended March 31, 2019, and 2018. Revenue Recognition Rental, Power, and Related Revenue We derive our revenues from leases with customers for data center and office and light-industrial space. Our leases include rental revenue lease components and nonlease revenue components, such as power and tenant reimbursements. We have elected to combine all of our nonlease revenue components that have the same pattern of transfer as the related operating lease component into a single combined lease component. Our leases with customers are classified as operating leases and rental revenue is recognized on a straight-line basis over the customer lease term. Occasionally, our customer leases include options to extend or terminate the lease agreements. We do not include any of these extension or termination options in a customer’s lease term for lease classification purposes or for recognizing rental revenue unless we are reasonably certain the customer will exercise these extension or termination options. The excess of rents recognized over amounts contractually due pursuant to the underlying leases is recorded as deferred rent receivable within other assets on our condensed consolidated balance sheets. In general, we provide two power products for our data center leased space, consisting of a fixed (breakered-amperage) and a variable (sub-metered) model. Customer power arrangements are coterminous with the customer’s underlying lease and have the same pattern of transfer over the lease term and are therefore combined with lease revenue within our condensed consolidated statements of operations. For variable power arrangements, a customer pays us variable monthly fees for the specific amount of power utilized at the current utility rates. We recognize variable power revenue each month as the uncertainty related to the consideration is resolved, as power is provided to our customers, and as our customers utilize the power. Some of our leases contain provisions under which our customers reimburse us for common area maintenance and other executory costs. These customer reimbursements are variable and are recognized in the period that the expenses are recognized. These services have the same pattern of transfer over the lease term and are also combined with lease revenue within our condensed consolidated statements of operations. Interconnection Revenue We also derive revenue from interconnection services, which are generally contracted on a month-to-month basis cancellable by us or the customer at any time. Interconnection services are accounted for as separate contracts and are not combined with lease and power arrangements. We recognize interconnection revenue each month as these services are delivered to, and utilized by, our customers. A provision for uncollectible accounts is recorded if a receivable balance relating to contractual rent, rental revenue recorded on a straight-line basis, tenant reimbursements or other billed amounts is considered by management to be uncollectible. At March 31, 2019, and December 31, 2018, the allowance for doubtful accounts totaled $0.3 million and $0.4 million, respectively, on the condensed consolidated balance sheets. Lessee Accounting We determine if an arrangement is a lease at inception. Our operating lease agreements are primarily for real estate space and are included within operating lease ROU assets and operating lease liabilities on the condensed consolidated balance sheets. We elected the practical expedient to combine our lease and related nonlease components for our lessee building leases. ROU assets represent our right to use an underlying asset for the lease term and lease liabilities represent our obligation to make lease payments arising from the lease. ROU assets and lease liabilities are recognized at the commencement date based on the present value of lease payments over the lease term. Our variable lease payments consist of nonlease services related to the lease. Variable lease payments are excluded from the ROU assets and lease liabilities and are recognized in the period in which the obligation for those payments is incurred. As most of our leases do not provide an implicit rate, we use our incremental borrowing rate based on the information available at commencement date in determining the present value of lease payments. ROU assets also include any lease payments made and exclude lease incentives. Many of our lessee agreements include options to extend the lease, which we do not include in our minimum lease terms unless they are reasonably certain to be exercised. Rental expense for lease payments related to operating leases is recognized on a straight-line basis over the lease term. 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 the Black-Scholes option-pricing model. The fair value of restricted share-based and Operating Partnership unit compensation is based on the fair value of our common stock on the date of the grant. The fair value of performance share awards, which have a market condition, is based on a Monte Carlo simulation. The fair value for all share-based compensation is amortized on a straight-line basis over the vesting period. We have elected to account for forfeitures as they occur. Asset Retirement and Environmental Remediation Obligations We record accruals for estimated asset retirement and environmental remediation obligations. The obligations relate primarily to the removal of asbestos during development of properties as well as the estimated equipment removal costs upon termination of a certain lease where we are the lessee. At March 31, 2019, and December 31, 2018, the amount included in unearned revenue, prepaid rent and other liabilities on the condensed consolidated balance sheets was approximately $1.6 million at each date. 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 generally are 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. 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 condensed consolidated financial statements for federal income taxes with regard to our activities and our subsidiary pass-through entities. The allocable share of taxable income is included in the income tax returns of its stockholders. We are subject to the statutory requirements of the locations in which we conduct 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. Deferred income taxes are recognized in certain taxable entities. Deferred income tax generally is 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 more likely than 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 March 31, 2019, and December 31, 2018, the gross deferred income taxes were not material. We currently have no liabilities for uncertain income tax positions. The earliest tax year for which we are subject to examination is 2015. 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 the Company is 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	3 Months Ended
	Mar. 31, 2019
Investment in Real Estate
Investment in Real Estate	3. Investment in Real Estate The following is a summary of the properties owned or leased by market at March 31, 2019 (in thousands): Buildings and Construction in Market Land Improvements Progress Total Cost Boston $ 5,154 $ 109,526 $ 678 $ 115,358 Chicago 5,493 114,188 26,362 146,043 Denver - 31,848 175 32,023 Los Angeles 18,672 339,080 67,173 424,925 Miami 728 14,166 42 14,936 New York 2,729 153,246 34,680 190,655 Northern Virginia 22,793 347,340 127,278 497,411 San Francisco Bay (1) 31,386 628,573 108,070 768,029 Total $ 86,955 $ 1,737,967 $ 364,458 $ 2,189,380 (1) On April 12, 2019, we acquired a 3.8-acre land parcel with a single-story office building located adjacent to our Santa Clara campus for a purchase price of $26 million. We expect to develop an approximately 200,000 NRSF turn-key data center building on the acquired land parcel, which we refer to as SV9, as the existing office tenants vacate upon expiration of their leases and upon the receipt of necessary entitlements.

Other Assets

Other Assets	3 Months Ended
	Mar. 31, 2019
Other Assets.
Other Assets	4. Other Assets Other assets consisted of the following, net of amortization and depreciation, if applicable for each line item, as of March 31, 2019, and December 31, 2018 (in thousands): March 31, December 31, 2019 2018 Deferred rent receivable $ 42,126 $ 43,162 Initial direct costs 23,875 24,651 Internal-use software 17,543 17,708 Prepaid expenses 10,480 7,090 Corporate furniture, fixtures and equipment 4,720 5,006 Deferred financing costs - revolving credit facility 2,660 2,880 Other 2,037 1,793 Total $ 103,441 $ 102,290

Leases

Leases	3 Months Ended
	Mar. 31, 2019
Leases
Leases	5. Leases As the lessee, we currently lease real estate space under noncancelable operating lease agreements for our turn-key data centers at NY1, LA1, LA4, DC1, DC2, DE1, and DE2, and our corporate headquarters located in Denver, Colorado. Our leases have remaining lease terms ranging from 1 year to 11 years, some of the leases include options to extend the leases for up to an additional 20 years. We do not include any of our renewal options in our lease terms for calculating our lease liability as the renewal options allow us to maintain operational flexibility and we are not reasonably certain we will exercise these renewal options at this time. The weighted-average remaining non-cancelable lease term for our operating leases was nine years and ten years at March 31, 2019, and December 31, 2018, respectively. The weighted-average discount rate was 4.9% at each date. The components of lease expense were as follows (in thousands): Three Months Ended March 31, 2019 2018 Lease expense: Operating lease expense $ 6,396 $ 5,227 Variable lease expense 1,292 1,173 Rent expense $ 7,688 $ 6,400

Lease Revenue

Lease Revenue	3 Months Ended
	Mar. 31, 2019
Lease Revenue
Lease Revenue	6. Lease Revenue The components of data center, office, light-industrial, and other lease revenue were as follows (in thousands): Three Months Ended March 31, 2019 2018 Lease revenue: Minimum lease revenue $ 99,410 $ 94,788 Variable lease revenue 21,069 18,271 Total lease revenue $ 120,479 $ 113,059

Debt

Debt	3 Months Ended
	Mar. 31, 2019
Debt
Debt	7. Debt A summary of outstanding indebtedness as of March 31, 2019, and December 31, 2018, is as follows (in thousands): Maturity March 31, December 31, Interest Rate Date 2019 2018 Revolving credit facility 3.94% and 3.95% at March 31, 2019, and December 31, 2018, respectively April 19, 2022 $ 291,000 $ 211,500 2020 Senior unsecured term loan (1) 3.36% and 3.37% at March 31, 2019, and December 31, 2018, respectively June 24, 2020 150,000 150,000 2021 Senior unsecured term loan 3.89% and 3.90% at March 31, 2019, and December 31, 2018, respectively February 2, 2021 100,000 100,000 2022 Senior unsecured term loan 3.89% and 3.65% at March 31, 2019, and December 31, 2018, respectively April 19, 2022 200,000 200,000 2023 Senior unsecured term loan (2) 4.00% and 4.01% at March 31, 2019, and December 31, 2018, respectively April 19, 2023 150,000 150,000 2023 Senior unsecured notes 4.19% at March 31, 2019, and December 31, 2018, respectively June 15, 2023 150,000 150,000 2024 Senior unsecured notes 3.91% at March 31, 2019, and December 31, 2018, respectively April 20, 2024 175,000 175,000 Total principal outstanding ` 1,216,000 1,136,500 Unamortized deferred financing costs (5,284) (5,677) Total debt $ 1,210,716 $ 1,130,823 (1) Our Operating Partnership has in place a swap agreement with respect to the 2020 Term Loan (as defined below), effective through May 5, 2020, to swap the variable interest rate associated with $75 million, or 50% of the principal amount, of the 2020 Term Loan to a fixed rate of approximately 2.83% per annum at our current leverage ratio as of March 31, 2019. The interest rate on the remaining $75 million of the 2020 Term Loan is based on the London Interbank Offered Rate (“LIBOR”) plus the applicable spread. The effective interest rate as of March 31, 2019, is 3.36%. See Note 8 – Derivatives and Hedging Activities. (2) Our Operating Partnership has in place a swap agreement with respect to the 2023 Term Loan (as defined below), effective through April 5, 2023, to swap the variable interest rate associated with $75 million, or 50% of the principal amount of the 2023 Term Loan, to a fixed rate of approximately 4.12% per annum at our current leverage ratio as of March 31, 2019. The interest rate on the remaining $75 million of the 2023 Term Loan is based on LIBOR plus the applicable spread. The effective interest rate as of March 31, 2019, is 4.00%. See Note 8 – Derivatives and Hedging Activities. Revolving Credit Facility On April 19, 2018, our Operating Partnership and certain subsidiary co-borrowers entered into the Fourth Amended and Restated Credit Agreement (as amended and restated, the “Amended and Restated Credit Agreement”), which amended and restated our previous credit agreement to provide additional liquidity of $250 million, which was used to pay down a portion of the then-existing revolving credit facility, fund continued development across our portfolio, and for general corporate purposes. The Amended and Restated Credit Agreement, among other things, increased the revolving credit facility from $350 million to $450 million, decreased the interest rates on borrowings under the revolving credit facility and certain term loans, and extended the maturity date from June 24, 2019, to April 19, 2022, with a one-time extension option, which, if exercised, would extend the maturity date to April 19, 2023. The exercise of the extension option is subject to the payment of an extension fee equal to 10 basis points of the total commitments under the Amended and Restated Credit Agreement at initial maturity and certain other customary conditions. The Amended and Restated Credit Agreement increased our total commitment from $600 million to $850 million, consisting of a $450 million revolving credit facility, a $150 million senior unsecured term loan scheduled to mature on June 24, 2020, a $100 million senior unsecured term loan scheduled to mature on February 2, 2021, and a new $150 million senior unsecured term loan scheduled to mature on April 19, 2023. See “2020 Senior Unsecured Term Loan,” “2021 Senior Unsecured Term Loan,” and “2023 Senior Unsecured Term Loan” below for a discussion of the $150 million, $100 million, and $150 million senior unsecured term loans, respectively. The Amended and Restated Credit Agreement also increased our accordion feature by $150 million to $350 million, which allows our Operating Partnership to increase the total commitments from $850 million to $1.2 billion, under specified circumstances, including securing capital from new or existing lenders. Borrowings under the revolving credit facility were amended to bear interest at a variable rate per annum equal to either (i) LIBOR plus 145 basis points to 205 basis points, or (ii) a base rate plus 45 basis points to 105 basis points, each depending on our Operating Partnership’s leverage ratio. At March 31, 2019, our Operating Partnership’s leverage ratio was 26.3% and the interest rate was LIBOR plus 145 basis points. The total amount available for borrowing under the revolving credit facility, is equal to the lesser of $450.0 million or the availability calculated based on our unencumbered asset pool. As of March 31, 2019, the borrowing capacity was $450.0 million. As of March 31, 2019, $291.0 million was borrowed and outstanding, $4.9 million was outstanding under letters of credit, and therefore $154.1 million remained available for us to borrow under the revolving credit facility. Our ability to borrow under the 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 total consolidated indebtedness to total gross asset value) of 60%, which, as of March 31, 2019, was 26.3% · a maximum secured debt ratio (defined as total consolidated secured debt to total gross asset value) of 40%, which, as of March 31, 2019, was 0.0% · a minimum fixed charge coverage ratio (defined as adjusted consolidated earnings before interest, taxes, depreciation and amortization to consolidated fixed charges) of 1.5 to 1.0, which, as of March 31, 2019, was 6.6 to 1.0. The Amended and Restated Credit Agreement ranks pari passu with the 2020 Term Loan, the 2021 Term Loan, the 2022 Term Loan, the 2023 Term Loan, the 2023 Notes, and the 2024 Notes (each as defined herein) and contains the same financial covenants and other customary restrictive covenants as those debt instruments. In connection with the Amended and Restated Credit Agreement, the revolving credit facility and senior unsecured term loans were amended to remove or change certain financial covenants and other customary restrictive covenants, including removal of covenants limiting distributions (except upon an event of default), incurrence of unhedged variable rate debt, and increases or decreases, as applicable to a number of ratios and other figures in the Amended and Restated Credit Agreement resulting in increased flexibility for our Operating Partnership. As of March 31, 2019, we were in compliance with all of the financial covenants under the Amended and Restated Credit Agreement. 2020 Senior Unsecured Term Loan Pursuant to the terms of the Amended and Restated Credit Agreement, our Operating Partnership and certain subsidiaries are party to a $150 million senior unsecured term loan (the “2020 Term Loan”), which was originally entered into on June 24, 2015. The 2020 Term Loan has a five-year term maturing on June 24, 2020. The 2020 Term Loan ranks pari passu with the 2021 Term Loan, the 2022 Term Loan, the 2023 Term Loan, the 2023 Notes, the 2024 Notes and the Amended and Restated Credit Agreement and contains the same financial covenants and other customary restrictive covenants as those debt instruments. As of March 31, 2019, we were in compliance with all of the financial covenants under the 2020 Term Loan. Borrowings under the 2020 Term Loan bear interest at a variable rate per annum equal to either (i) LIBOR plus 140 basis points to 200 basis points, or (ii) a base rate plus 40 basis points to 100 basis points, each depending on our Operating Partnership's leverage ratio. At March 31, 2019, the Operating Partnership’s leverage ratio was 26.3% and the interest rate was LIBOR plus 140 basis points. 2021 Senior Unsecured Term Loan On February 2, 2016, our Operating Partnership and certain subsidiaries partially exercised the accordion feature on our term loans under the Amended and Restated Credit Agreement and entered into a $100 million senior unsecured term loan (the “2021 Term Loan”). The 2021 Term Loan is governed by the terms of the Amended and Restated Credit Agreement. The 2021 Term Loan has a five-year term maturing on February 2, 2021. The 2021 Term Loan ranks pari passu with the 2020 Term Loan, the 2022 Term Loan, the 2023 Term Loan, the 2023 Notes, the 2024 Notes and the Amended and Restated Credit Agreement and contains the same financial covenants and other customary restrictive covenants as those debt instruments. As of March 31, 2019, we were in compliance with all of the financial covenants under the 2021 Term Loan. Borrowings under the 2021 Term Loan bear interest at a variable rate per annum equal to either (i) LIBOR plus 140 basis points to 200 basis points, or (ii) a base rate plus 40 basis points to 100 basis points, each depending on our Operating Partnership’s leverage ratio. At March 31, 2019, our Operating Partnership’s leverage ratio was 26.3% and the interest rate was LIBOR plus 140 basis points. 2022 Senior Unsecured Term Loan On April 19, 2017, our Operating Partnership and certain subsidiaries entered into an Amended and Restated Term Loan Agreement (as amended and restated, the “Term Loan Agreement”), which amended and restated the $100 million senior unsecured term loan, originally entered into on January 31, 2014. The Term Loan Agreement was amended and restated to, among other things, (i) exercise the accordion feature to increase the total commitments to $200 million, (ii) extend the maturity of the term loan from January 31, 2019, to April 19, 2022, (iii) amend the accordion feature to allow an increase in total commitments from $200 million to $300 million, under specified circumstances, including securing capital from new or existing lenders, and (iv) explicitly permit the issuance of the 2024 Notes defined below (the “2024 Notes”). The 2022 Term Loan ranks pari passu with the 2020 Term Loan, the 2021 Term Loan, the 2023 Term Loan, the 2023 Notes, the 2024 Notes and the Amended and Restated Credit Agreement and contains the same financial covenants and other customary restrictive covenants as those debt instruments. As of March 31, 2019, we were in compliance with all of the financial covenants under the 2022 Term Loan. Borrowings under the 2022 Term Loan bear interest at a variable rate per annum equal to either (i) LIBOR plus 140 basis points to 200 basis points, or (ii) a base rate plus 40 basis points to 100 basis points, each depending on our Operating Partnership's leverage ratio. At March 31, 2019, our Operating Partnership’s leverage ratio was 26.3% and the interest rate was LIBOR plus 140 basis points. 2023 Senior Unsecured Term Loan On April 19, 2018, pursuant to the terms of, the Amended and Restated Credit Agreement, our Operating Partnership and certain subsidiaries entered into a $150 million senior unsecured term loan (the “2023 Term Loan”). The 2023 Term Loan has a five-year term maturing on April 19, 2023. The 2023 Term Loan ranks pari passu with the 2020 Term Loan, the 2021 Term Loan, the 2022 Term Loan, the 2023 Notes, the 2024 Notes and the Amended and Restated Credit Agreement and contains the same financial covenants and other customary restrictive covenants as those debt instruments. As of March 31, 2019, we were in compliance with all of the financial covenants under the 2023 Term Loan. Borrowings under the 2023 Term Loan bear interest at a variable rate per annum equal to either (i) LIBOR plus 140 basis points to 200 basis points, or (ii) a base rate plus 40 basis points to 100 basis points, each depending on our Operating Partnership’s leverage ratio. At March 31, 2019, our Operating Partnership’s leverage ratio was 26.3% and the interest rate was LIBOR plus 140 basis points. 2023 Senior Unsecured Notes On June 15, 2016, our Operating Partnership issued an aggregate principal amount of $150 million, 4.19% senior unsecured notes due June 15, 2023 (the “2023 Notes”), in a private placement to certain accredited investors. The terms of the 2023 Notes are governed by a note purchase agreement, dated June 15, 2016 (the “2023 Note Purchase Agreement”), by and among our Operating Partnership, the Company and the purchasers of the 2023 Notes. Interest is payable semiannually, on the 15 th day of June and December of each year, commencing on December 15, 2016. The 2023 Notes are senior unsecured obligations of our Operating Partnership and are jointly and severally guaranteed by the Company and each of our Operating Partnership’s subsidiaries that guarantees indebtedness under our Amended and Restated Credit Agreement (the “Subsidiary Guarantors”). Our Operating Partnership may prepay all or a portion of the 2023 Notes upon notice to the holders for 100% of the principal amount so prepaid plus a make-whole premium as set forth in the 2023 Note Purchase Agreement. Upon the occurrence of certain change of control events, holders of the 2023 Notes have the right to require our Operating Partnership to purchase 100% of such holder’s 2023 Notes in cash at a purchase price equal to 100% of the principal amount thereof plus accrued and unpaid interest, if any, to the date of repurchase. The 2023 Notes rank pari passu with the 2020 Term Loan, the 2021 Term Loan, the 2022 Term Loan, the 2023 Term Loan, the 2024 Notes and the Amended and Restated Credit Agreement. On June 12, 2018, the 2023 Note Purchase Agreement was amended to, among other things, conform to the same financial covenants as the Amended and Restated Credit Agreement, as described above. In addition, certain additional financial covenants in the Amended and Restated Credit Agreement were automatically incorporated into the 2023 Note Purchase Agreement, and, subject to certain conditions, these additional financial covenants will be deleted, removed, amended or otherwise modified to be more or less restrictive if the analogous covenant in the Credit Agreement is so deleted, removed, amended or otherwise modified. These covenants are subject to a number of exceptions and qualifications set forth in the 2023 Note Purchase Agreement. As of March 31, 2019, we were in compliance with all of the financial covenants under the 2023 Note Purchase Agreement. 2024 Senior Unsecured Notes On April 20, 2017, our Operating Partnership issued an aggregate principal amount of $175 million, 3.91% senior unsecured notes due April 20, 2024 (the “2024 Notes”), in a private placement to certain accredited investors. The terms of the 2024 Notes are governed by a note purchase agreement, dated April 20, 2017 (the “2024 Note Purchase Agreement”), by and among our Operating Partnership, the Company and the purchasers of the 2024 Notes. Interest is payable semiannually, on the 15 th day of June and December of each year, commencing on December 15, 2017. The 2024 Notes are senior unsecured obligations of our Operating Partnership and are jointly and severally guaranteed by the Company and each of the Subsidiary Guarantors. Our Operating Partnership may prepay all or a portion of the 2024 Notes upon notice to the holders for 100% of the principal amount so prepaid plus a make-whole premium as set forth in the 2024 Note Purchase Agreement. Upon the occurrence of certain change of control events, holders of the 2024 Notes will have the right to require our Operating Partnership to purchase 100% of such holders’ 2024 Notes in cash at a purchase price equal to 100% of the principal amount thereof plus accrued and unpaid interest, if any, to the date of repurchase. The 2024 Notes rank pari passu with the 2020 Term Loan, the 2021 Term Loan, the 2022 Term Loan, the 2023 Term Loan, the 2023 Notes and the Amended and Restated Credit Agreement. On June 12, 2018, the 2024 Note Purchase Agreement was amended to, among other things, conform to the same financial covenants as the Amended and Restated Credit Agreement, as described above. In addition, certain additional financial covenants in the Amended and Restated Credit Agreement were automatically incorporated into the 2024 Note Purchase Agreement, and, subject to certain conditions, these additional financial covenants will be deleted, removed, amended or otherwise modified to be more or less restrictive if the analogous covenant in the Amended and Restated Credit Agreement is so deleted, removed, amended or otherwise modified. These covenants are subject to a number of exceptions and qualifications set forth in the 2024 Note Purchase Agreement. As of March 31, 2019, we were in compliance with all of the financial covenants under the 2024 Note Purchase Agreement. Debt Maturities The following table summarizes when our debt currently becomes due, adjusted for the April 2019 debt financing transactions discussed below, and the subsequent payment of outstanding amounts on the revolving credit facility (in thousands): Year Ending December 31, 2019 $ — 2020 150,000 2021 100,000 2022 200,000 2023 300,000 Thereafter 466,000 Total principal outstanding 1,216,000 Unamortized deferred financing costs (5,284) Total debt, net $ 1,210,716 Subsequent Debt Financing On April 17, 2019, our Operating Partnership entered into a note purchase agreement (the “Note Purchase Agreement”) pursuant to which the Operating Partnership agreed to issue and sell an aggregate principal amount of $200 million of the Operating Partnership’s 4.11% Series A Senior Notes (the “Series A Notes”) due April 17, 2026, and $200 million of its 4.31% Series B Senior Notes (the “Series B Notes” and, together with the Series A Notes, the “Notes”) due April 17, 2029. In connection with the issuance of the Notes, on April 3, 2019, we settled our $175 million forward-starting seven-year interest rate swap. After giving effect to cancellation costs incurred in connection with the termination of this swap agreement entered into in anticipation of the issuance of the Notes, the Series A Notes will bear an effective interest rate of 4.52% per annum. An aggregate principal amount of $200 million of the Series A Notes and $125 million of the Series B Notes were issued on April 17, 2019. The Operating Partnership expects to issue $75 million aggregate principal amount of the Series B Notes prior to July 17, 2019. Interest on the Notes is payable semiannually on the 15 th day of August and February in each year, commencing on February 15, 2020. The Notes rank pari passu with the 2020 Term Loan, the 2021 Term Loan, the 2022 Term Loan, the 2023 Term Loan, the 2023 Notes, the 2024 Notes and the Amended and Restated Credit Agreement. The Notes are senior unsecured obligations of the Operating Partnership and are jointly and severally guaranteed by the Company and each of the Operating Partnership’s subsidiaries that guarantees indebtedness under its senior unsecured credit facilities. The Operating Partnership used the proceeds from the Notes to pay down outstanding amounts on the revolving portion of its senior unsecured credit facilities, and it will use the remaining proceeds for general corporate purposes.

Derivatives and Hedging Activit

Derivatives and Hedging Activities	3 Months Ended
	Mar. 31, 2019
Derivatives and Hedging Activities
Derivatives and Hedging Activities	8. Derivatives and Hedging Activities Notional Amount Fair Value (Level 2) (1) March 31, December 31, Type of Strike Rate Effective Expiration March 31, December 31, 2019 2018 Derivative as of 3/31/19 Date Date 2019 2018 $ — $ 50,000 Swap — % 2/28/2014 1/31/2019 (2) $ — $ 43 75,000 75,000 Swap 5/5/2015 5/5/2020 773 1,099 75,000 75,000 Swap 5/5/2018 5/5/2023 (1,661) (897) 175,000 175,000 Swap (3) 6/3/2019 (3) 6/3/2026 (3) (6,718) (3,183) $ 325,000 $ 375,000 $ (7,606) $ (2,938) (1) Derivatives are recorded at fair value in our condensed consolidated balance sheets in other assets and unearned revenue, prepaid rent and other liabilities. We do not net our derivative position by counterparty for purposes of balance sheet presentation and disclosure. We had $8.4 million and $4.1 million in derivative liabilities recognized in unearned revenue, prepaid rent and other liabilities in our consolidated balance sheets as of March 31, 2019, and December 31, 2018, respectively. We also had $0.8 million and $1.1 million derivative assets recognized in other assets in our consolidated balance sheets as of March 31, 2019, and December 31, 2018, respectively. (2) On January 31, 2019, the remaining $50 million of a five-year interest rate swap agreement, which reduced our variability in cash flows relating to interest payments based on one-month LIBOR variable rate debt, expired. (3) On December 6, 2018, we entered into forward-starting seven-year interest rate swap agreement to protect against adverse fluctuations in interest rates. The swap effectively fixed the interest rate at approximately 2.91% per annum plus the applicable spread. On April 3, 2019, we settled the $175 million forward-starting seven-year interest rate swap, in connection with the anticipated subsequent debt issuance of $200 million of the Series A Notes, at a loss of $5.7 million. The loss will be included in accumulated other comprehensive income and will be amortized to interest expense over the term of the new seven-year Senior A Notes. See Note 7 – Debt for additional discussion of the subsequent debt financing. Risk Management Objective of Using Derivatives We are exposed to certain risks arising from both our business operations and economic conditions. We principally manage our exposures to a wide variety of business and operational risks through management of our core business activities. We manage economic risks, including interest rate, liquidity, and credit risk primarily by managing the amount, sources, and duration of our debt funding and the use of derivative financial instruments. Specifically, we enter into derivative financial instruments to manage exposures that arise from business activities that result in the receipt or payment of future known or uncertain cash amounts, the value of which are determined by interest rates. Our derivative financial instruments are used to manage differences in the amount, timing, and duration of our known or expected cash receipts and our known or expected cash payments principally related to our investments and borrowings. Cash Flow Hedges of Interest Rate Risk Our objectives in using interest rate derivatives are to reduce variability in interest expense and to manage our exposure to adverse interest rate movements. To accomplish this objective, we primarily use interest rate swaps as part of our interest rate risk management strategy. Interest rate swaps designated as cash flow hedges involve the receipt of variable amounts from a counterparty in exchange for the Company making fixed-rate payments over the life of the agreements without exchange of the underlying notional amount. The changes in the fair value of derivatives designated and that qualify as effective cash flow hedges is recorded in accumulated other comprehensive income or loss on the condensed consolidated balance sheets and is subsequently reclassified into earnings in the period that the hedged forecasted transaction affects earnings. The amounts recorded in other comprehensive income or loss related to the unrealized gain or loss on derivative contracts were losses of ($4.5) million and gains $0.6 million for the three months ended March 31, 2019, and 2018, respectively. The amounts reclassified from other comprehensive income (loss) to interest expense on the condensed consolidated statements of operations were ($0.2) million and less than ($0.1) million for the three months ended March 31, 2019, and 2018. Total interest expense included in the condensed consolidated statements of operations in which the effects of cash flow hedges are recorded was $9.5 million and $7.7 million for the three months ended March 31, 2019, and 2018, respectively. Amounts reported in accumulated other comprehensive income related to derivatives will be reclassified to interest expense as interest payments are made on our variable-rate debt. During the subsequent twelve months, beginning April 1, 2019, we estimate that $0.3 million will be reclassified as an increase to interest expense.

Stockholders' Equity

Stockholders' Equity	3 Months Ended
	Mar. 31, 2019
Stockholders' Equity
Stockholders' Equity	9. Stockholders’ Equity We announced the following dividends per share on our common stock during the three months ended March 31, 2019: Declaration Date Record Date Payment Date Common Stock March 7, 2019 March 29, 2019 April 15, 2019 $ 1.10

Noncontrolling Interests - Oper

Noncontrolling Interests - Operating Partnership	3 Months Ended
	Mar. 31, 2019
Noncontrolling Interests - Operating Partnership
Noncontrolling Interests - Operating Partnership	10. Noncontrolling Interests — Operating Partnership Noncontrolling interests represent the limited partnership interests in our Operating Partnership held by individuals and entities other than CoreSite Realty Corporation. The current holders of common Operating Partnership units are eligible to have the common Operating Partnership units redeemed for cash or common stock on a one-for-one basis, at our option. The following table shows the common ownership interests in our Operating Partnership as of March 31, 2019, and December 31, 2018: March 31, 2019 December 31, 2018 Number of Units Percentage of Total Number of Units Percentage of Total CoreSite Realty Corporation 36,409,337 75.9 % 36,256,032 75.8 % Noncontrolling interests 11,575,268 24.1 11,575,268 24.2 Total 47,984,605 100.0 % 47,831,300 100.0 % For each share of common stock issued by us, our Operating Partnership issues to us an equivalent common Operating Partnership unit. During the three months ended March 31, 2019, we issued 153,305 shares of common stock related to employee compensation arrangements and therefore an equivalent number of common Operating Partnership units were issued to us by our Operating Partnership. Holders of common Operating Partnership units received aggregate distributions of $1.10 per unit during the three months ended March 31, 2019, payable in correlation with declared dividends on shares of our common stock. The redemption value of the noncontrolling interests at March 31, 2019, was $1.2 billion based on the closing price of the Company’s common stock of $107.02 per share on the last trading day prior to that date.

Equity Incentive Plan

Equity Incentive Plan	3 Months Ended
	Mar. 31, 2019
Equity Incentive Award Plan
Equity Incentive Plan	11. Equity Incentive Plan Our Board of Directors adopted and, with the approval of our stockholders, amended the 2010 Equity Incentive Plan (as amended, the “2010 Plan”) in 2013. The 2010 Plan is administered by the Compensation Committee of our Board of Directors. Awards issuable under the 2010 Plan include common stock, stock options, restricted stock, stock appreciation rights, dividend equivalents, Operating Partnership units and other incentive awards. 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 unvested shares subject to the award will be available for future grant or sale under the 2010 Plan. Shares of restricted stock that are forfeited or repurchased by us pursuant to the 2010 Plan may again be 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 March 31, 2019, 2,661,409 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 on 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. The fair values are amortized on a straight-line basis over the vesting periods. Stock options have not been granted since the year ended December 31, 2013. The following table sets forth stock option activity under the 2010 Plan for the three months ended March 31, 2019: Number of Shares Weighted- Subject to Average Option Exercise Price Options outstanding, December 31, 2018 49,133 $ 20.06 Granted — — Exercised (1,129) 15.23 Forfeited — — Expired — — Options outstanding, March 31, 2019 48,004 $ 20.17 As of March 31, 2019, all stock option awards are fully vested. Restricted Stock Awards and Units Restricted stock awards and restricted stock units, or RSUs, are granted with a fair value equal to the closing market price of the Company’s common stock on the date of grant. The principal difference between restricted stock awards and RSUs is that RSUs are not shares of our 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 a share of common stock. The restricted stock awards and RSUs are amortized on a straight-line basis to expense over the vesting period. The following table sets forth the number of unvested restricted stock awards and RSUs and the weighted-average fair value of these awards at the date of grant: Restricted Weighted- Stock Average Fair Awards and Value at Grant Units Date Unvested balance, December 31, 2018 284,879 $ 85.98 Granted 147,881 100.38 Forfeited (1,698) 88.05 Vested (109,287) 77.73 Unvested balance, March 31, 2019 321,775 $ 95.39 As of March 31, 2019, total unearned compensation on restricted stock awards and RSUs was approximately $28.8 million, and the weighted-average vesting period was 2.9 years. Performance Stock Awards We grant long-term incentives to members of management in the form of performance-based restricted stock awards (“PSAs”) under the 2010 Plan. The number of PSAs earned is based on our achievement of relative total shareholder return (“TSR”) measured versus the MSCI US REIT Index over a three-year performance period and ranges between 25% and 175% of the target number of shares for PSAs granted in 2017, 2018, and 2019. The PSAs are granted at the maximum percentage of target and are retired annually to the extent we do not meet the maximum relative TSR performance threshold versus the MSCI US REIT Index. The PSAs are earned upon TSR achievement measured both annually and over the full three-year performance period. The PSAs have a service condition and will be released at the end of the three-year performance period, to the extent earned, provided that the holder continues to be employed or otherwise in service of the Company at the end of the three-year performance period. The PSAs are amortized on a straight-line basis to expense over the vesting period. Holders of the PSAs are entitled to dividends on the PSAs, which are accrued and paid in cash at the end of the three-year performance period. The following table sets forth the number of unvested PSAs and the weighted-average fair value of these awards at the date of grant: Weighted- Average Fair Performance-Based Restricted Stock Awards Value at Grant Minimum Maximum Target Date Unvested balance, December 31, 2018 50,823 173,944 112,385 $ 96.58 Granted 10,926 76,480 43,703 114.55 Performance adjustment (1) 18,063 (29,819) (5,878) — Forfeited — — — — Vested (43,650) (43,650) (43,650) 84.78 Unvested balance, March 31, 2019 36,162 176,955 106,560 $ 107.69 (1) Includes the annual adjustment for the number of PSAs earned based on our achievement of relative TSR measured versus the MSCI US REIT Index for the applicable performance periods. As of March 31, 2019, total unearned compensation on PSAs was approximately $9.1 million, and the weighted-average vesting period was 2.5 years. The fair value of each PSA award is estimated on the date of grant using a Monte Carlo simulation. The simulation requires assumptions for expected volatility, risk-free rate of return, and dividend yield. The following table summarizes the assumptions used to value the PSAs granted during the three months ended March 31, 2019, and 2018. Three Months Ended March 31, 2019 2018 Expected term (in years) 2.82 2.82 Expected volatility 24.09 % 24.15 % Expected annual dividend (1) — — Risk-free rate 2.48 % 2.24 % (1) The fair value of the PSAs assumes reinvestment of dividends.

Earnings Per Share

Earnings Per Share	3 Months Ended
	Mar. 31, 2019
Earnings Per Share
Earnings Per Share	12. Earnings Per Share Basic net income per share is calculated by dividing the net income attributable to common shares by the weighted-average number of common shares outstanding during the period. Diluted net income per share adjusts basic net income per share for the effects of potentially dilutive common shares, if the effect is not antidilutive. Potentially dilutive common stock consists of shares issuable under the 2010 Plan. The following is a summary of basic and diluted net income per share (in thousands, except share and per share amounts): Three Months Ended March 31, 2019 2018 Net income attributable to common shares $ 19,661 $ 20,302 Weighted-average common shares outstanding - basic 36,347,781 33,935,564 Effect of potentially dilutive common shares: Stock options 38,921 53,813 Unvested awards 160,363 174,858 Weighted-average common shares outstanding - diluted 36,547,065 34,164,235 Net income per share attributable to common shares Basic $ 0.54 $ 0.60 Diluted $ 0.54 $ 0.59 In the calculations above, we have excluded weighted-average potentially dilutive securities of 39,754 and 37,760 for the three months ended March 31, 2019, and 2018, respectively, as their effect would have been antidilutive.

Estimated Fair Value of Financi

Estimated Fair Value of Financial Instruments	3 Months Ended
	Mar. 31, 2019
Estimated Fair Value of Financial Instruments
Estimated Fair Value of Financial Instruments	13. 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, accounts and other receivables, interest rate swaps, the revolving credit facility, the senior unsecured term loans, senior unsecured notes, interest payable and accounts payable. The carrying values of cash and cash equivalents, accounts and other receivables, interest payable and accounts payable approximate fair values due to the short-term nature of these financial instruments. The interest rate swaps are recorded at fair value. The valuation of our derivatives is determined using widely accepted valuation techniques including discounted cash flow analysis on the expected cash flows of each derivative, which reflects the contractual terms of the derivatives, including the period to maturity, and uses observable market-based inputs, including interest rate curves. We have determined that the majority of the inputs used to value our derivatives fall within Level 2 of the fair value hierarchy; however, the credit valuation adjustments associated with our derivatives utilize Level 3 inputs, such as estimates of current credit spreads, to evaluate the likelihood of default by our Operating Partnership and its counterparties. As of March 31, 2019, we have assessed the significance of the impact of the credit valuation adjustments on the overall valuation of our derivative positions and have determined that the credit valuation adjustment is not significant to the overall valuation of our derivative portfolio. As a result, we classify our derivative valuation in Level 2 of the fair value hierarchy. The total principal balance of our revolving credit facility, senior unsecured term loans, and senior unsecured notes was $1,216.0 million and $1,136.5 million as of March 31, 2019, and December 31, 2018, respectively, with a fair value of $1,217.7 million and $1,131.8 million, respectively, based on Level 3 inputs from the fair value hierarchy. Under the discounted cash flow method, the fair values of the revolving credit facility and the senior unsecured term loans are based on our assumptions of market interest rates and terms available incorporating our credit risk for similar loan maturities. Our lease liabilities are determined based on the estimated present value of our minimum lease payments under our lease agreements. The discount rate used to determine the lease liabilities is based on our estimated incremental borrowing rate, based on Level 3 inputs from the fair value hierarchy.

Commitments and Contingencies

Commitments and Contingencies	3 Months Ended
	Mar. 31, 2019
Commitments and Contingencies.
Commitments and Contingencies	14. Commitments and Contingencies Our properties require periodic investments of capital for general capital improvements and for tenant-related capital expenditures. We enter into various construction and equipment contracts with third parties for the development of our properties. At March 31, 2019, we had open commitments related to construction contracts of approximately $188.7 million. Additionally, we have commitments related to telecommunications capacity used to connect data centers located within the same market or geographical area, power usage, and company-wide improvements that are ancillary to revenue generation. At March 31, 2019, we had open commitments related to these contracts of approximately $75.5 million, of which $7.4 million is scheduled to be met during the remainder of the year ended December 31, 2019. In the ordinary course of business, we are subject to claims and administrative proceedings. We are not presently party to any proceeding, which we believe to be material or which we would expect to have, individually or in the aggregate, a material adverse effect on our business, financial condition, cash flows or results of operations. The outcome of litigation and administrative proceedings is inherently uncertain. Therefore, if one or more legal or administrative matters are resolved against us in a reporting period for amounts in excess of management’s expectations, our financial condition, cash flows or results of operations for that reporting period could be materially adversely affected.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	3 Months Ended
	Mar. 31, 2019
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 U.S. Securities and Exchange Commission. Accordingly, these unaudited 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 three months ended March 31, 2019, are not necessarily indicative of the expected results for the year ending December 31, 2019. These unaudited 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, 2018. Our Operating Partnership meets the definition and criteria of a variable interest entity (“VIE”) and we are the primary beneficiary of the VIE. Our sole significant asset is the investment in our Operating Partnership, and consequently, substantially all of our assets and liabilities represent those assets and liabilities of our Operating Partnership. Our debt is an obligation of our Operating Partnership where the creditors also have recourse against the credit of the Company. Intercompany balances and transactions have been eliminated upon consolidation.
Recent Accounting Pronouncements	Recent Accounting Pronouncements Not Yet Adopted Fair Value Measurement In August 2018, the Financial Accounting Standards Board (“FASB”) issued guidance codified in Accounting Standards Update (“ASU”) 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework – Changes to the Disclosure Requirements for Fair Value Measurement. ASU 2018-13 improves the overall usefulness of disclosures to financial statement users and reduces unnecessary costs in preparing fair value measurement disclosures. The standard will be effective for interim and annual reporting periods beginning after December 15, 2019, with early adoption permitted. We do not expect the provisions of ASU 2018-13 to have a material impact on our condensed consolidated financial statements. Intangibles – Goodwill and Other – Internal-Use Software In August 2018, the FASB issued guidance codified in ASU 2018-15, Intangibles – Goodwill and Other – Internal-Use Software (Subtopic 350-40): Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract. ASU 2018-15 clarifies that implementation costs incurred by customers in cloud computing arrangements are deferred if they would be capitalized by customers in software licensing arrangements under the internal-use software guidance. Additionally, ASU 2018-15 clarifies that all capitalized costs must be presented in the same financial statement line item as the cloud computing arrangement. The standard will be effective, on either a prospective or retrospective basis, for interim and annual reporting periods beginning after December 15, 2019, with early adoption permitted. We are currently evaluating the provisions of ASU 2018-15 and whether the provisions will have a material impact on our condensed consolidated financial statements. We determined that all other recently issued accounting pronouncements will not have a material impact on our consolidated financial statements or do not apply to our operations.
Use of Estimates	Use of Estimates The preparation of these unaudited 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 unaudited 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 our standalone selling prices, performance-based equity compensation plans and the carrying values of our real estate properties, goodwill, and accrued liabilities. 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.
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 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, rent expense and internal costs of personnel performing development, if such costs are incremental and identifiable to a specific development project. Capitalization of costs begins upon commencement of development efforts and ceases when the project 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 $2.6 million and $1.1 million for the three months ended March 31, 2019, and 2018, 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 10 years Leasehold improvements The shorter of the lease term or useful life of the asset Depreciation expense was $32.2 million and $29.1 million for the three months ended March 31, 2019, and 2018, respectively.
Acquisition of Investment in Real Estate	Acquisition of Investment in Real Estate When accounting for business combinations and asset acquisitions, the fair value of the real estate acquired is allocated to the acquired tangible assets, consisting primarily of land, building and building 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 primary difference between business combinations and asset acquisitions is that asset acquisitions require cost accumulation and allocation at a relative fair value. Acquisition costs are capitalized for asset acquisitions and expensed for business combinations. 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 market lease rates for the corresponding in-place leases, measured over a period equal to the remaining noncancelable term of the lease and, for below-market leases, over a time 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 revenue, 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. 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 related to these intangible assets was recognized for the three months ended March 31, 2019, or 2018. 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 March 31, 2019, and December 31, 2018, we had $40.6 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 months ended March 31, 2019, or 2018.
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.
Initial Direct Costs	Initial Direct Costs Initial direct costs include commissions paid to third parties, including brokers, leasing and referral agents, and internal sales commissions paid to employees for successful execution of lease agreements. Initial direct costs are incremental costs that would not have been incurred if the lease agreement had not been executed. These initial direct costs are capitalized and generally amortized over the term of the related leases using the straight-line method. If a customer lease terminates prior to the expiration of its initial term, any unamortized initial direct costs related to the lease are written off to amortization expense. Amortization of initial direct costs were $3.4 million and $3.9 million for the three months ended March 31, 2019, and 2018, respectively. Initial direct costs are included within other assets in the condensed consolidated balance sheets and consisted of the following, net of amortization, as of March 31, 2019, and December 31, 2018 (in thousands): March 31, December 31, 2019 2018 Internal sales commissions $ 13,732 $ 14,199 Third party commissions 9,594 9,855 Other 549 597 Total $ 23,875 $ 24,651
Deferred Financing Costs	Deferred Financing Costs 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 indebtedness and the amortization is included as a component of interest expense. Depending on the type of debt instrument, deferred financing costs are reported either in other assets or as a direct deduction from the carrying amount of the related debt liabilities in our condensed consolidated balance sheets.
Recoverability of Long-Lived Assets	Recoverability of Long-Lived Assets We review our 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 months ended March 31, 2019, and 2018, no impairment of long-lived assets was recognized in the condensed consolidated financial statements.
Derivative Instruments and Hedging Activities	Derivative Instruments and Hedging Activities We reflect all derivative instruments at fair value as either assets or liabilities on the condensed consolidated balance sheets. For those derivative instruments that are designated and qualify as hedging instruments, we record the gain or loss on the hedging instruments as a component of accumulated other comprehensive income or loss. For derivatives that do not meet the criteria for hedge accounting, changes in fair value are immediately recognized within net income. See additional discussion in Note 8, Derivatives and Hedging Activities.
Internal-Use Software	Internal-Use Software We recognize internal-use software development costs based on the development stage of the project and nature of the cost. Internal and external costs incurred during the preliminary project stage are expensed as they are incurred. Internal and external costs incurred to develop internal-use software during the application development stage are capitalized. Internal and external training costs and maintenance costs during the post-implementation-operation stage are expensed as incurred. Completed projects are placed into service and amortized over the estimated useful life of the software. No impairment of internal-use software was recognized in the condensed consolidated financial statements for the three months ended March 31, 2019, and 2018.
Revenue Recognition	Revenue Recognition Rental, Power, and Related Revenue We derive our revenues from leases with customers for data center and office and light-industrial space. Our leases include rental revenue lease components and nonlease revenue components, such as power and tenant reimbursements. We have elected to combine all of our nonlease revenue components that have the same pattern of transfer as the related operating lease component into a single combined lease component. Our leases with customers are classified as operating leases and rental revenue is recognized on a straight-line basis over the customer lease term. Occasionally, our customer leases include options to extend or terminate the lease agreements. We do not include any of these extension or termination options in a customer’s lease term for lease classification purposes or for recognizing rental revenue unless we are reasonably certain the customer will exercise these extension or termination options. The excess of rents recognized over amounts contractually due pursuant to the underlying leases is recorded as deferred rent receivable within other assets on our condensed consolidated balance sheets. In general, we provide two power products for our data center leased space, consisting of a fixed (breakered-amperage) and a variable (sub-metered) model. Customer power arrangements are coterminous with the customer’s underlying lease and have the same pattern of transfer over the lease term and are therefore combined with lease revenue within our condensed consolidated statements of operations. For variable power arrangements, a customer pays us variable monthly fees for the specific amount of power utilized at the current utility rates. We recognize variable power revenue each month as the uncertainty related to the consideration is resolved, as power is provided to our customers, and as our customers utilize the power. Some of our leases contain provisions under which our customers reimburse us for common area maintenance and other executory costs. These customer reimbursements are variable and are recognized in the period that the expenses are recognized. These services have the same pattern of transfer over the lease term and are also combined with lease revenue within our condensed consolidated statements of operations. Interconnection Revenue We also derive revenue from interconnection services, which are generally contracted on a month-to-month basis cancellable by us or the customer at any time. Interconnection services are accounted for as separate contracts and are not combined with lease and power arrangements. We recognize interconnection revenue each month as these services are delivered to, and utilized by, our customers. A provision for uncollectible accounts is recorded if a receivable balance relating to contractual rent, rental revenue recorded on a straight-line basis, tenant reimbursements or other billed amounts is considered by management to be uncollectible. At March 31, 2019, and December 31, 2018, the allowance for doubtful accounts totaled $0.3 million and $0.4 million, respectively, on the condensed consolidated balance sheets.
Lessee Accounting	Lessee Accounting We determine if an arrangement is a lease at inception. Our operating lease agreements are primarily for real estate space and are included within operating lease ROU assets and operating lease liabilities on the condensed consolidated balance sheets. We elected the practical expedient to combine our lease and related nonlease components for our lessee building leases. ROU assets represent our right to use an underlying asset for the lease term and lease liabilities represent our obligation to make lease payments arising from the lease. ROU assets and lease liabilities are recognized at the commencement date based on the present value of lease payments over the lease term. Our variable lease payments consist of nonlease services related to the lease. Variable lease payments are excluded from the ROU assets and lease liabilities and are recognized in the period in which the obligation for those payments is incurred. As most of our leases do not provide an implicit rate, we use our incremental borrowing rate based on the information available at commencement date in determining the present value of lease payments. ROU assets also include any lease payments made and exclude lease incentives. Many of our lessee agreements include options to extend the lease, which we do not include in our minimum lease terms unless they are reasonably certain to be exercised. Rental expense for lease payments related to operating leases is recognized on a straight-line basis over the lease term.
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 the Black-Scholes option-pricing model. The fair value of restricted share-based and Operating Partnership unit compensation is based on the fair value of our common stock on the date of the grant. The fair value of performance share awards, which have a market condition, is based on a Monte Carlo simulation. The fair value for all share-based compensation is amortized on a straight-line basis over the vesting period. We have elected to account for forfeitures as they occur.
Asset Retirement and Environmental Remediation Obligations	Asset Retirement and Environmental Remediation Obligations We record accruals for estimated asset retirement and environmental remediation obligations. The obligations relate primarily to the removal of asbestos during development of properties as well as the estimated equipment removal costs upon termination of a certain lease where we are the lessee. At March 31, 2019, and December 31, 2018, the amount included in unearned revenue, prepaid rent and other liabilities on the condensed consolidated balance sheets was approximately $1.6 million at each date.
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 generally are 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. 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 condensed consolidated financial statements for federal income taxes with regard to our activities and our subsidiary pass-through entities. The allocable share of taxable income is included in the income tax returns of its stockholders. We are subject to the statutory requirements of the locations in which we conduct 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. Deferred income taxes are recognized in certain taxable entities. Deferred income tax generally is 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 more likely than 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 March 31, 2019, and December 31, 2018, the gross deferred income taxes were not material. We currently have no liabilities for uncertain income tax positions. The earliest tax year for which we are subject to examination is 2015.
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 the Company is 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 Accoun_3

Summary of Significant Accounting Policies (Tables)	3 Months Ended
	Mar. 31, 2019
Summary of Significant Accounting Policies
Schedule of useful lives of real estate investment assets	Buildings 27 to 40 years Building improvements 1 to 10 years Leasehold improvements The shorter of the lease term or useful life of the asset
Schedule of deferred leasing costs, net of amortization	Initial direct costs are included within other assets in the condensed consolidated balance sheets and consisted of the following, net of amortization, as of March 31, 2019, and December 31, 2018 (in thousands): March 31, December 31, 2019 2018 Internal sales commissions $ 13,732 $ 14,199 Third party commissions 9,594 9,855 Other 549 597 Total $ 23,875 $ 24,651

Investment in Real Estate (Tabl

Investment in Real Estate (Tables)	3 Months Ended
	Mar. 31, 2019
Investment in Real Estate
Summary of properties owned or leased	The following is a summary of the properties owned or leased by market at March 31, 2019 (in thousands): Buildings and Construction in Market Land Improvements Progress Total Cost Boston $ 5,154 $ 109,526 $ 678 $ 115,358 Chicago 5,493 114,188 26,362 146,043 Denver - 31,848 175 32,023 Los Angeles 18,672 339,080 67,173 424,925 Miami 728 14,166 42 14,936 New York 2,729 153,246 34,680 190,655 Northern Virginia 22,793 347,340 127,278 497,411 San Francisco Bay (1) 31,386 628,573 108,070 768,029 Total $ 86,955 $ 1,737,967 $ 364,458 $ 2,189,380 (1) On April 12, 2019, we acquired a 3.8-acre land parcel with a single-story office building located adjacent to our Santa Clara campus for a purchase price of $26 million. We expect to develop an approximately 200,000 NRSF turn-key data center building on the acquired land parcel, which we refer to as SV9, as the existing office tenants vacate upon expiration of their leases and upon the receipt of necessary entitlements.

Other Assets (Tables)

Other Assets (Tables)	3 Months Ended
	Mar. 31, 2019
Other Assets.
Schedule of other assets	Other assets consisted of the following, net of amortization and depreciation, if applicable for each line item, as of March 31, 2019, and December 31, 2018 (in thousands): March 31, December 31, 2019 2018 Deferred rent receivable $ 42,126 $ 43,162 Initial direct costs 23,875 24,651 Internal-use software 17,543 17,708 Prepaid expenses 10,480 7,090 Corporate furniture, fixtures and equipment 4,720 5,006 Deferred financing costs - revolving credit facility 2,660 2,880 Other 2,037 1,793 Total $ 103,441 $ 102,290

Leases (Tables)

Leases (Tables)	3 Months Ended
	Mar. 31, 2019
Leases
Schedule of components of lease expense	Three Months Ended March 31, 2019 2018 Lease expense: Operating lease expense $ 6,396 $ 5,227 Variable lease expense 1,292 1,173 Rent expense $ 7,688 $ 6,400

Lease Revenue (Tables)

Lease Revenue (Tables)	3 Months Ended
	Mar. 31, 2019
Lease Revenue
Components of data center, office, light-industrial, and other lease revenue	The components of data center, office, light-industrial, and other lease revenue were as follows (in thousands): Three Months Ended March 31, 2019 2018 Lease revenue: Minimum lease revenue $ 99,410 $ 94,788 Variable lease revenue 21,069 18,271 Total lease revenue $ 120,479 $ 113,059

Debt (Tables)

Debt (Tables)	3 Months Ended
	Mar. 31, 2019
Debt
Summary of outstanding indebtedness	7. Debt A summary of outstanding indebtedness as of March 31, 2019, and December 31, 2018, is as follows (in thousands): Maturity March 31, December 31, Interest Rate Date 2019 2018 Revolving credit facility 3.94% and 3.95% at March 31, 2019, and December 31, 2018, respectively April 19, 2022 $ 291,000 $ 211,500 2020 Senior unsecured term loan (1) 3.36% and 3.37% at March 31, 2019, and December 31, 2018, respectively June 24, 2020 150,000 150,000 2021 Senior unsecured term loan 3.89% and 3.90% at March 31, 2019, and December 31, 2018, respectively February 2, 2021 100,000 100,000 2022 Senior unsecured term loan 3.89% and 3.65% at March 31, 2019, and December 31, 2018, respectively April 19, 2022 200,000 200,000 2023 Senior unsecured term loan (2) 4.00% and 4.01% at March 31, 2019, and December 31, 2018, respectively April 19, 2023 150,000 150,000 2023 Senior unsecured notes 4.19% at March 31, 2019, and December 31, 2018, respectively June 15, 2023 150,000 150,000 2024 Senior unsecured notes 3.91% at March 31, 2019, and December 31, 2018, respectively April 20, 2024 175,000 175,000 Total principal outstanding ` 1,216,000 1,136,500 Unamortized deferred financing costs (5,284) (5,677) Total debt $ 1,210,716 $ 1,130,823 (1) Our Operating Partnership has in place a swap agreement with respect to the 2020 Term Loan (as defined below), effective through May 5, 2020, to swap the variable interest rate associated with $75 million, or 50% of the principal amount, of the 2020 Term Loan to a fixed rate of approximately 2.83% per annum at our current leverage ratio as of March 31, 2019. The interest rate on the remaining $75 million of the 2020 Term Loan is based on the London Interbank Offered Rate (“LIBOR”) plus the applicable spread. The effective interest rate as of March 31, 2019, is 3.36%. See Note 8 – Derivatives and Hedging Activities. (2) Our Operating Partnership has in place a swap agreement with respect to the 2023 Term Loan (as defined below), effective through April 5, 2023, to swap the variable interest rate associated with $75 million, or 50% of the principal amount of the 2023 Term Loan, to a fixed rate of approximately 4.12% per annum at our current leverage ratio as of March 31, 2019. The interest rate on the remaining $75 million of the 2023 Term Loan is based on LIBOR plus the applicable spread. The effective interest rate as of March 31, 2019, is 4.00%. See Note 8 – Derivatives and Hedging Activities.
Summary of amount of the entity's outstanding debt when such debt currently become due	Year Ending December 31, 2019 $ — 2020 150,000 2021 100,000 2022 200,000 2023 300,000 Thereafter 466,000 Total principal outstanding 1,216,000 Unamortized deferred financing costs (5,284) Total debt, net $ 1,210,716

Derivatives and Hedging Activ_2

Derivatives and Hedging Activities (Tables)	3 Months Ended
	Mar. 31, 2019
Derivatives and Hedging Activities
Schedule of derivative instruments	Notional Amount Fair Value (Level 2) (1) March 31, December 31, Type of Strike Rate Effective Expiration March 31, December 31, 2019 2018 Derivative as of 3/31/19 Date Date 2019 2018 $ — $ 50,000 Swap — % 2/28/2014 1/31/2019 (2) $ — $ 43 75,000 75,000 Swap 5/5/2015 5/5/2020 773 1,099 75,000 75,000 Swap 5/5/2018 5/5/2023 (1,661) (897) 175,000 175,000 Swap (3) 6/3/2019 (3) 6/3/2026 (3) (6,718) (3,183) $ 325,000 $ 375,000 $ (7,606) $ (2,938) (1) Derivatives are recorded at fair value in our condensed consolidated balance sheets in other assets and unearned revenue, prepaid rent and other liabilities. We do not net our derivative position by counterparty for purposes of balance sheet presentation and disclosure. We had $8.4 million and $4.1 million in derivative liabilities recognized in unearned revenue, prepaid rent and other liabilities in our consolidated balance sheets as of March 31, 2019, and December 31, 2018, respectively. We also had $0.8 million and $1.1 million derivative assets recognized in other assets in our consolidated balance sheets as of March 31, 2019, and December 31, 2018, respectively. (2) On January 31, 2019, the remaining $50 million of a five-year interest rate swap agreement, which reduced our variability in cash flows relating to interest payments based on one-month LIBOR variable rate debt, expired. (3) On December 6, 2018, we entered into forward-starting seven-year interest rate swap agreement to protect against adverse fluctuations in interest rates. The swap effectively fixed the interest rate at approximately 2.91% per annum plus the applicable spread. On April 3, 2019, we settled the $175 million forward-starting seven-year interest rate swap, in connection with the anticipated subsequent debt issuance of $200 million of the Series A Notes, at a loss of $5.7 million. The loss will be included in accumulated other comprehensive income and will be amortized to interest expense over the term of the new seven-year Senior A Notes. See Note 7 – Debt for additional discussion of the subsequent debt financing.

Stockholders' Equity (Tables)

Stockholders' Equity (Tables)	3 Months Ended
	Mar. 31, 2019
Stockholders' Equity
Schedule of dividends paid per share on Series A Cumulative Preferred Stock and common shares	Declaration Date Record Date Payment Date Common Stock March 7, 2019 March 29, 2019 April 15, 2019 $ 1.10

Noncontrolling Interests - Op_2

Noncontrolling Interests - Operating Partnership (Tables)	3 Months Ended
	Mar. 31, 2019
Noncontrolling Interests - Operating Partnership
Schedule of ownership interests in our Operating Partnership	March 31, 2019 December 31, 2018 Number of Units Percentage of Total Number of Units Percentage of Total CoreSite Realty Corporation 36,409,337 75.9 % 36,256,032 75.8 % Noncontrolling interests 11,575,268 24.1 11,575,268 24.2 Total 47,984,605 100.0 % 47,831,300 100.0 %

Equity Incentive Award Plan (Ta

Equity Incentive Award Plan (Tables)	3 Months Ended
	Mar. 31, 2019
Equity Incentive Award Plan
Schedule of stock option activity	Number of Shares Weighted- Subject to Average Option Exercise Price Options outstanding, December 31, 2018 49,133 $ 20.06 Granted — — Exercised (1,129) 15.23 Forfeited — — Expired — — Options outstanding, March 31, 2019 48,004 $ 20.17
Schedule of restricted awards and RSUs	Restricted Weighted- Stock Average Fair Awards and Value at Grant Units Date Unvested balance, December 31, 2018 284,879 $ 85.98 Granted 147,881 100.38 Forfeited (1,698) 88.05 Vested (109,287) 77.73 Unvested balance, March 31, 2019 321,775 $ 95.39
Schedule of unvested PSAs and their weighted-average fair value at the date of grant	Weighted- Average Fair Performance-Based Restricted Stock Awards Value at Grant Minimum Maximum Target Date Unvested balance, December 31, 2018 50,823 173,944 112,385 $ 96.58 Granted 10,926 76,480 43,703 114.55 Performance adjustment (1) 18,063 (29,819) (5,878) — Forfeited — — — — Vested (43,650) (43,650) (43,650) 84.78 Unvested balance, March 31, 2019 36,162 176,955 106,560 $ 107.69 (1) Includes the annual adjustment for the number of PSAs earned based on our achievement of relative TSR measured versus the MSCI US REIT Index for the applicable performance periods.
Summary of assumptions used to value stock option awards	Three Months Ended March 31, 2019 2018 Expected term (in years) 2.82 2.82 Expected volatility 24.09 % 24.15 % Expected annual dividend (1) — — Risk-free rate 2.48 % 2.24 % (1) The fair value of the PSAs assumes reinvestment of dividends.

Earnings Per Share (Tables)

Earnings Per Share (Tables)	3 Months Ended
	Mar. 31, 2019
Earnings Per Share
Summary of basic and diluted income per share	The following is a summary of basic and diluted net income per share (in thousands, except share and per share amounts): Three Months Ended March 31, 2019 2018 Net income attributable to common shares $ 19,661 $ 20,302 Weighted-average common shares outstanding - basic 36,347,781 33,935,564 Effect of potentially dilutive common shares: Stock options 38,921 53,813 Unvested awards 160,363 174,858 Weighted-average common shares outstanding - diluted 36,547,065 34,164,235 Net income per share attributable to common shares Basic $ 0.54 $ 0.60 Diluted $ 0.54 $ 0.59

Organization and Description _2

Organization and Description of Business (Details) - Operating partnership	Mar. 31, 2019	Dec. 31, 2018
Coresite Realty Corporation
Organization
Percentage of ownership interests held by the entity	75.90%	75.80%
Noncontrolling interests
Organization
Percentage of ownership interests held by others	24.10%	24.20%
Carlyle Group
Organization
Percentage of ownership interests held by others	24.10%

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Real Estate (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Investments in Real Estate
Capitalized interest costs	$ 2.6	$ 1.1
Depreciation expense	$ 32.2	$ 29.1
Building | Minimum
Investments in Real Estate
Useful lives	27 years
Building | 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	10 years

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Deferred Costs & Impairment (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Summary of Significant Accounting Policies
Impairment loss related to intangible assets	$ 0	$ 0
Goodwill	40,646		$ 40,646
Impairment loss related to goodwill	0	0
Deferred Costs
Amortization of initial direct costs	3,400	3,900
Internal sales commissions	13,732		14,199
Third party commissions	9,594		9,855
Other	549		597
Total	23,875		$ 24,651
Recoverability of Long-Lived Assets
Impairment of long-lived assets	$ 0	$ 0

Summary of Significant Accoun_6

Summary of Significant Accounting Policies - Internal Use Software, RR & IT (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Internal-Use Software
Recognized impairment of internal use software	$ 0	$ 0
Revenue Recognition
Allowance for doubtful accounts (in dollars)	283		$ 417
Asset Retirement and Environmental Remediation Obligations
Asset retirement and environmental remediation obligations	$ 1,600		$ 1,600
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

Summary of Significant Accoun_7

Summary of Significant Accounting Policies - Concentration of Credit Risks & Segment Information (Details)	3 Months Ended
	Mar. 31, 2019segmentitem
Summary of Significant Accounting Policies
Number of off-balance-sheet concentrations of credit risk | item	0
Segment information
Number of reportable segments | segment	1

Investment in Real Estate (Deta

Investment in Real Estate (Details) $ in Thousands	Apr. 12, 2019USD ($)ft²a	Mar. 31, 2019USD ($)	Dec. 31, 2018USD ($)
Investment in Real Estate
Land		$ 86,955	$ 86,955
Buildings and Improvements		1,737,967	1,730,329
Construction in progress		364,458	$ 265,921
Total investments in real estate		2,189,380
Subsequent Event
Investment in Real Estate
Area of land | a	3.8
Purchase price	$ 26,000
Net rentable space (in square feet) | ft²	200,000
Boston
Investment in Real Estate
Land		5,154
Buildings and Improvements		109,526
Construction in progress		678
Total investments in real estate		115,358
Chicago
Investment in Real Estate
Land		5,493
Buildings and Improvements		114,188
Construction in progress		26,362
Total investments in real estate		146,043
Denver
Investment in Real Estate
Buildings and Improvements		31,848
Construction in progress		175
Total investments in real estate		32,023
Los Angeles
Investment in Real Estate
Land		18,672
Buildings and Improvements		339,080
Construction in progress		67,173
Total investments in real estate		424,925
Miami
Investment in Real Estate
Land		728
Buildings and Improvements		14,166
Construction in progress		42
Total investments in real estate		14,936
New York
Investment in Real Estate
Land		2,729
Buildings and Improvements		153,246
Construction in progress		34,680
Total investments in real estate		190,655
Northern Virginia
Investment in Real Estate
Land		22,793
Buildings and Improvements		347,340
Construction in progress		127,278
Total investments in real estate		497,411
San Francisco Bay
Investment in Real Estate
Land		31,386
Buildings and Improvements		628,573
Construction in progress		108,070
Total investments in real estate		$ 768,029

Other Assets (Details)

Other Assets (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Other Assets.
Deferred rent receivable	$ 42,126	$ 43,162
Initial direct costs	23,875	24,651
Internal-use software	17,543	17,708
Prepaid expense	10,480	7,090
Corporate furniture, fixtures and equipment	4,720	5,006
Deferred financing costs - revolving credit facility	2,660	2,880
Other	2,037	1,793
Total	$ 103,441	$ 102,290

Leases - (Detail)

Leases - (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Lease terms
Option to extend	P20Y
Weighted-average remaining lease term	9 years		10 years
Weighted-average discount rate	4.90%		4.90%
Lease expense
Operating lease expense	$ 6,396	$ 5,227
Variable lease expense	1,292	1,173
Rent expense	$ 7,688	$ 6,400
Weighted-average remaining lease term	9 years		10 years
Minimum
Lease terms
Remaining lease terms	1 year
Maximum
Lease terms
Remaining lease terms	11 years

Lease Revenue (Details)

Lease Revenue (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Components of lease revenue
Minimum lease revenue	$ 99,410	$ 94,788
Variable lease revenue	21,069	18,271
Total lease revenue	$ 120,479	$ 113,059

Debt - Summary of Debt (Details

Debt - Summary of Debt (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Debt
Total principal outstanding	$ 1,216,000	$ 1,136,500
Unamortized deferred financing costs	(5,284)	(5,677)
Total debt	$ 1,210,716	$ 1,130,823
Revolving Credit Facility
Debt
Interest rate as of reporting date (as a percent)	3.94%	3.95%
Total principal outstanding	$ 291,000	$ 211,500
2020 Senior Unsecured Term Loan | Senior Unsecured Term Loan
Debt
Interest rate as of reporting date (as a percent)	3.36%	3.37%
Total principal outstanding	$ 150,000	$ 150,000
2021 Senior Unsecured Term Loan | Senior Unsecured Term Loan
Debt
Interest rate as of reporting date (as a percent)	3.89%	3.90%
Total principal outstanding	$ 100,000	$ 100,000
2022 Senior Unsecured Term Loan | Senior Unsecured Term Loan
Debt
Interest rate as of reporting date (as a percent)	3.89%	3.65%
Total principal outstanding	$ 200,000	$ 200,000
2023 Senior Unsecured Term Loan | Senior Unsecured Term Loan
Debt
Interest rate as of reporting date (as a percent)	4.00%	4.01%
Total principal outstanding	$ 150,000	$ 150,000
Amount of debt hedged	$ 75,000
Percentage of debt hedged	50.00%
Amount of debt not hedged	$ 75,000
Derivative, Fixed Interest Rate	4.12%
2023 Senior Unsecured Term Loan | Senior Unsecured Notes
Debt
Interest rate as of reporting date (as a percent)	4.19%	4.19%
Total principal outstanding	$ 150,000	$ 150,000
2024 Senior Unsecured Term Loan
Debt
Interest rate as of reporting date (as a percent)	3.91%	3.91%
2024 Senior Unsecured Term Loan | Senior Unsecured Term Loan
Debt
Total principal outstanding	$ 175,000	$ 175,000
Operating partnership | 2020 Senior Unsecured Term Loan
Debt
Amount of debt not hedged	75,000
Operating partnership | 2020 Senior Unsecured Term Loan | Interest Rate Swap
Debt
Amount of debt hedged	$ 75,000
Percentage of debt hedged	50.00%
Derivative, Fixed Interest Rate	2.83%

Debt - Revolving Credit Facilit

Debt - Revolving Credit Facility (Details) $ in Thousands	Apr. 19, 2018USD ($)item	Feb. 02, 2016USD ($)	Jun. 24, 2015USD ($)	Mar. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Apr. 18, 2018USD ($)	Apr. 19, 2017USD ($)
Debt
Total principal outstanding				$ 1,216,000	$ 1,136,500
Revolving Credit Facility
Debt
Total principal outstanding				$ 291,000	211,500
Credit Agreement
Debt
Leverage ratio (as a percent)				26.30%
Secured debt ratio, Covenant (as a percent)				0.00%
Fixed charge coverage ratio				6.6
Credit Agreement | Minimum
Debt
Fixed charge coverage ratio				1.50
Credit Agreement | Maximum
Debt
Leverage ratio (as a percent)				0.60%
Secured debt ratio (as a percent)				0.40%
2023 Senior Unsecured Term Loan
Debt
Term of loan facility	5 years
Unsecured term loan	$ 150,000
2023 Senior Unsecured Term Loan | LIBOR | Minimum
Debt
Interest rate margin (as a percent)	1.40%
2023 Senior Unsecured Term Loan | LIBOR | Maximum
Debt
Interest rate margin (as a percent)	2.00%
2023 Senior Unsecured Term Loan | Base Rate | Minimum
Debt
Interest rate margin (as a percent)	0.40%
2023 Senior Unsecured Term Loan | Base Rate | Maximum
Debt
Interest rate margin (as a percent)	1.00%
2023 Senior Unsecured Term Loan | Senior Unsecured Term Loan
Debt
Total principal outstanding				$ 150,000	150,000
2020 Senior Unsecured Term Loan | Senior Unsecured Term Loan
Debt
Total principal outstanding				150,000	150,000
2021 Senior Unsecured Term Loan | Senior Unsecured Term Loan
Debt
Total principal outstanding				100,000	100,000
2022 Senior Unsecured Term Loan | Senior Unsecured Term Loan
Debt
Total principal outstanding				$ 200,000	$ 200,000
Operating partnership | LIBOR
Debt
Interest rate margin (as a percent)				1.45%
Operating partnership | Credit Agreement
Debt
Number of options available for extensions | item	1
Extension fee (as a percent)	0.10%
Total increase in commitment under accordion feature	$ 250,000
Maximum borrowing capacity	850,000					$ 600,000
Maximum borrowing capacity including accordion feature	1,200,000
Borrowing capacity at end of period				$ 450,000
Letters of credit outstanding				4,900
Amount available for borrowing under the facility				$ 154,100
Operating partnership | Credit Agreement | Revolving Credit Facility
Debt
Maximum borrowing capacity	450,000					$ 350,000
Operating partnership | Credit Agreement | Revolving Credit Facility | LIBOR | Minimum
Debt
Interest rate margin (as a percent)				1.45%
Operating partnership | Credit Agreement | Revolving Credit Facility | LIBOR | Maximum
Debt
Interest rate margin (as a percent)				2.05%
Operating partnership | Credit Agreement | Revolving Credit Facility | Base Rate | Minimum
Debt
Interest rate margin (as a percent)				0.45%
Operating partnership | Credit Agreement | Revolving Credit Facility | Base Rate | Maximum
Debt
Interest rate margin (as a percent)				1.05%
Operating partnership | 2020 Senior Unsecured Term Loan | LIBOR
Debt
Interest rate margin (as a percent)				1.40%
Operating partnership | 2020 Senior Unsecured Term Loan | LIBOR | Minimum
Debt
Interest rate margin (as a percent)				1.40%
Operating partnership | 2020 Senior Unsecured Term Loan | LIBOR | Maximum
Debt
Interest rate margin (as a percent)				2.00%
Operating partnership | 2020 Senior Unsecured Term Loan | Base Rate | Minimum
Debt
Interest rate margin (as a percent)				0.40%
Operating partnership | 2020 Senior Unsecured Term Loan | Base Rate | Maximum
Debt
Interest rate margin (as a percent)				1.00%
Operating partnership | 2020 Senior Unsecured Term Loan | Senior Unsecured Term Loan
Debt
Term of loan facility			5 years
Unsecured term loan	$ 150,000		$ 150,000
Operating partnership | 2021 Senior Unsecured Term Loan | LIBOR
Debt
Interest rate margin (as a percent)				1.40%
Operating partnership | 2021 Senior Unsecured Term Loan | LIBOR | Minimum
Debt
Interest rate margin (as a percent)				1.40%
Operating partnership | 2021 Senior Unsecured Term Loan | LIBOR | Maximum
Debt
Interest rate margin (as a percent)				2.00%
Operating partnership | 2021 Senior Unsecured Term Loan | Base Rate | Minimum
Debt
Interest rate margin (as a percent)				0.40%
Operating partnership | 2021 Senior Unsecured Term Loan | Base Rate | Maximum
Debt
Interest rate margin (as a percent)				1.00%
Operating partnership | 2021 Senior Unsecured Term Loan | Senior Unsecured Term Loan
Debt
Term of loan facility		5 years
Unsecured term loan		$ 100,000
Operating partnership | 2022 Senior Unsecured Term Loan | LIBOR
Debt
Interest rate margin (as a percent)				1.40%
Operating partnership | 2022 Senior Unsecured Term Loan | LIBOR | Minimum
Debt
Interest rate margin (as a percent)				1.40%
Operating partnership | 2022 Senior Unsecured Term Loan | LIBOR | Maximum
Debt
Interest rate margin (as a percent)				2.00%
Operating partnership | 2022 Senior Unsecured Term Loan | Base Rate | Minimum
Debt
Interest rate margin (as a percent)				0.40%
Operating partnership | 2022 Senior Unsecured Term Loan | Base Rate | Maximum
Debt
Interest rate margin (as a percent)				1.00%
Operating partnership | 2022 Senior Unsecured Term Loan | Senior Unsecured Term Loan
Debt
Increase in accordion feature borrowing capacity							$ 300,000

Debt - Unsecured Debt (Details)

Debt - Unsecured Debt (Details) - USD ($) $ in Thousands	Apr. 19, 2018	Feb. 02, 2016	Jun. 24, 2015	Mar. 31, 2019	Dec. 31, 2018	Apr. 20, 2017	Apr. 19, 2017	Jun. 15, 2016
Debt
Total principal outstanding				$ 1,216,000	$ 1,136,500
2020 Senior Unsecured Term Loan | Senior Unsecured Term Loan
Debt
Total principal outstanding				$ 150,000	$ 150,000
Debt Instrument, Interest Rate at Period End				3.36%	3.37%
2021 Senior Unsecured Term Loan | Senior Unsecured Term Loan
Debt
Total principal outstanding				$ 100,000	$ 100,000
Debt Instrument, Interest Rate at Period End				3.89%	3.90%
2022 Senior Unsecured Term Loan | Senior Unsecured Term Loan
Debt
Total principal outstanding				$ 200,000	$ 200,000
Debt Instrument, Interest Rate at Period End				3.89%	3.65%
2023 Senior Unsecured Term Loan
Debt
Unsecured term loan	$ 150,000
Term of loan facility	5 years
2023 Senior Unsecured Term Loan | LIBOR | Minimum
Debt
Interest rate margin (as a percent)	1.40%
2023 Senior Unsecured Term Loan | LIBOR | Maximum
Debt
Interest rate margin (as a percent)	2.00%
2023 Senior Unsecured Term Loan | Base Rate | Minimum
Debt
Interest rate margin (as a percent)	0.40%
2023 Senior Unsecured Term Loan | Base Rate | Maximum
Debt
Interest rate margin (as a percent)	1.00%
2023 Senior Unsecured Term Loan | Senior Unsecured Term Loan
Debt
Total principal outstanding				$ 150,000	$ 150,000
Debt Instrument, Interest Rate at Period End				4.00%	4.01%
2023 Senior Unsecured Term Loan | Senior Unsecured Notes
Debt
Total principal outstanding				$ 150,000	$ 150,000
Debt Instrument, Interest Rate at Period End				4.19%	4.19%
2024 Senior Unsecured Term Loan
Debt
Debt Instrument, Interest Rate at Period End				3.91%	3.91%
2024 Senior Unsecured Term Loan | Senior Unsecured Term Loan
Debt
Total principal outstanding				$ 175,000	$ 175,000
Operating partnership | LIBOR
Debt
Interest rate margin (as a percent)				1.45%
Operating partnership | 2020 Senior Unsecured Term Loan | LIBOR
Debt
Interest rate margin (as a percent)				1.40%
Operating partnership | 2020 Senior Unsecured Term Loan | LIBOR | Minimum
Debt
Interest rate margin (as a percent)				1.40%
Operating partnership | 2020 Senior Unsecured Term Loan | LIBOR | Maximum
Debt
Interest rate margin (as a percent)				2.00%
Operating partnership | 2020 Senior Unsecured Term Loan | Base Rate | Minimum
Debt
Interest rate margin (as a percent)				0.40%
Operating partnership | 2020 Senior Unsecured Term Loan | Base Rate | Maximum
Debt
Interest rate margin (as a percent)				1.00%
Operating partnership | 2020 Senior Unsecured Term Loan | Senior Unsecured Term Loan
Debt
Unsecured term loan	$ 150,000		$ 150,000
Term of loan facility			5 years
Operating partnership | 2021 Senior Unsecured Term Loan | LIBOR
Debt
Interest rate margin (as a percent)				1.40%
Operating partnership | 2021 Senior Unsecured Term Loan | LIBOR | Minimum
Debt
Interest rate margin (as a percent)				1.40%
Operating partnership | 2021 Senior Unsecured Term Loan | LIBOR | Maximum
Debt
Interest rate margin (as a percent)				2.00%
Operating partnership | 2021 Senior Unsecured Term Loan | Base Rate | Minimum
Debt
Interest rate margin (as a percent)				0.40%
Operating partnership | 2021 Senior Unsecured Term Loan | Base Rate | Maximum
Debt
Interest rate margin (as a percent)				1.00%
Operating partnership | 2021 Senior Unsecured Term Loan | Senior Unsecured Term Loan
Debt
Unsecured term loan		$ 100,000
Term of loan facility		5 years
Operating partnership | 2022 Senior Unsecured Term Loan | LIBOR
Debt
Interest rate margin (as a percent)				1.40%
Operating partnership | 2022 Senior Unsecured Term Loan | LIBOR | Minimum
Debt
Interest rate margin (as a percent)				1.40%
Operating partnership | 2022 Senior Unsecured Term Loan | LIBOR | Maximum
Debt
Interest rate margin (as a percent)				2.00%
Operating partnership | 2022 Senior Unsecured Term Loan | Base Rate | Minimum
Debt
Interest rate margin (as a percent)				0.40%
Operating partnership | 2022 Senior Unsecured Term Loan | Base Rate | Maximum
Debt
Interest rate margin (as a percent)				1.00%
Operating partnership | 2022 Senior Unsecured Term Loan | Senior Unsecured Term Loan
Debt
Increase in accordion feature borrowing capacity							$ 300,000
Aggregate principal amount							$ 200,000
Operating partnership | 2023 Senior Unsecured Term Loan | Senior Unsecured Notes | Private Placement
Debt
Aggregate principal amount								$ 150,000
Stated interest rate								4.19%
Percentage of term notes that may be prepaid								100.00%
Percentage of term notes that holders have right to purchase in cash								100.00%
Percentage of term notes that holders may redeem for cash								100.00%
Operating partnership | 2024 Senior Unsecured Term Loan | Senior Unsecured Term Loan
Debt
Unsecured term loan						$ 175,000
Stated interest rate						3.91%
Percentage of term notes that may be prepaid						100.00%
Percentage of term notes that holders have right to purchase in cash						100.00%
Percentage of term notes that holders may redeem for cash						100.00%

Debt - Maturities (Details)

Debt - Maturities (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Debt maturities
2020	$ 150,000
2021	100,000
2022	200,000
2023	300,000
Thereafter	466,000
Total principal outstanding	1,216,000	$ 1,136,500
Unamortized deferred financing costs	(5,284)	(5,677)
Total debt	$ 1,210,716	$ 1,130,823

Debt - Subsequent Debt Financin

Debt - Subsequent Debt Financing (Details) - USD ($) $ in Thousands	Apr. 03, 2019	Jan. 31, 2019	Dec. 06, 2018	Jul. 17, 2019	Apr. 17, 2019	Mar. 31, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Outstanding amount						$ 1,216,000	$ 1,136,500
Interest Rate Swap | Designated as Hedging Instrument
Debt Instrument [Line Items]
Derivative terminated or settled		$ 50,000
Term		5 years	7 years
Subsequent Event | Interest Rate Swap | Designated as Hedging Instrument
Debt Instrument [Line Items]
Derivative terminated or settled	$ 175,000
Subsequent Event | Senior Notes | Series A Notes
Debt Instrument [Line Items]
Aggregate principal amount	200,000
Subsequent Event | Operating partnership | Interest Rate Swap | Designated as Hedging Instrument
Debt Instrument [Line Items]
Derivative terminated or settled	$ 175,000
Term	7 years
Subsequent Event | Operating partnership | Senior Notes | Series A Notes
Debt Instrument [Line Items]
Aggregate principal amount					$ 200,000
Interest rate (as a percent)					4.11%
Effective interest rate					4.52%
Outstanding amount					$ 200,000
Subsequent Event | Operating partnership | Senior Notes | Series B Notes
Debt Instrument [Line Items]
Aggregate principal amount					$ 200,000
Interest rate (as a percent)					4.31%
Outstanding amount					$ 125,000
Subsequent Event | Operating partnership | Senior Notes | Series B Notes | Forecast
Debt Instrument [Line Items]
Outstanding amount				$ 75,000

Derivatives and Hedging Activ_3

Derivatives and Hedging Activities (Details) - USD ($) $ in Thousands	Apr. 03, 2019	Jan. 31, 2019	Dec. 06, 2018	Apr. 19, 2018	Mar. 31, 2019	Mar. 31, 2018	Sep. 30, 2019	Dec. 31, 2018
Derivative instruments and hedging activities disclosures
Amount of gain (loss) recorded in accumulated other comprehensive income					$ (4,466)	$ 609
Interest expense					9,498	7,738
Interest Rate Swap | Designated as Hedging Instrument
Derivative instruments and hedging activities disclosures
Notional Amount					325,000			$ 375,000
Strike Rate			2.91%
Derivative liabilities recognized in unearned revenue, prepaid rent and other liabitilies					8,400			4,100
Derivative asset recognized in other assets					800			1,100
Derivative terminated or settled		$ 50,000
Term		5 years	7 years
Interest Rate Swap | Designated as Hedging Instrument | Subsequent Event
Derivative instruments and hedging activities disclosures
Derivative terminated or settled	$ 175,000
Amount of loss recorded in accumulated other comprehensive income	5,700
Interest Rate Swap | Designated as Hedging Instrument | Cash Flow Hedging
Derivative instruments and hedging activities disclosures
Amount of gain (loss) recorded in accumulated other comprehensive income					(4,500)	600
Amount reclassified to interest expense					(200)	(100)
Interest expense					9,500	$ 7,700
Interest Rate Swap | Designated as Hedging Instrument | Cash Flow Hedging | Forecast
Derivative instruments and hedging activities disclosures
Amount estimated to be reclassified as an increase to interest expense							$ 300
Interest Rate Swap | Designated as Hedging Instrument | Level 2
Derivative instruments and hedging activities disclosures
Fair Value					(7,606)			(2,938)
Interest rate swap expiring 1/31/2019 | Designated as Hedging Instrument
Derivative instruments and hedging activities disclosures
Notional Amount								50,000
Interest rate swap expiring 1/31/2019 | Designated as Hedging Instrument | Level 2
Derivative instruments and hedging activities disclosures
Fair Value								43
Interest rate swap expiring 5/20/2015 | Designated as Hedging Instrument
Derivative instruments and hedging activities disclosures
Notional Amount					$ 75,000			75,000
Strike Rate					2.83%
Interest rate swap expiring 5/20/2015 | Designated as Hedging Instrument | Level 2
Derivative instruments and hedging activities disclosures
Fair Value					$ 773			1,099
Interest rate swap expiring 5/5/2023 | Designated as Hedging Instrument
Derivative instruments and hedging activities disclosures
Notional Amount					$ 75,000			75,000
Strike Rate					4.12%
Interest rate swap expiring 5/5/2023 | Designated as Hedging Instrument | Level 2
Derivative instruments and hedging activities disclosures
Fair Value					$ (1,661)			(897)
Interest rate swap expiring 6/3/2026 | Designated as Hedging Instrument
Derivative instruments and hedging activities disclosures
Notional Amount					$ 175,000			175,000
Strike Rate					2.91%
Interest rate swap expiring 6/3/2026 | Designated as Hedging Instrument | Level 2
Derivative instruments and hedging activities disclosures
Fair Value					$ (6,718)			$ (3,183)
Series A Notes | Senior Notes | Subsequent Event
Derivative instruments and hedging activities disclosures
Debt face amount	$ 200,000
Debt Term	7 years
2023 Senior Unsecured Term Loan
Derivative instruments and hedging activities disclosures
Debt Term				5 years

Stockholders' Equity (Details)

Stockholders' Equity (Details) - Common Stock	Mar. 07, 2019$ / shares
Stockholders' Equity
Dividends Payable, Date of Record	Mar. 29, 2019
Common Stock dividend declared (per share)	$ 1.10

Noncontrolling Interests - Op_3

Noncontrolling Interests - Operating Partnership (Details) $ / shares in Units, $ in Billions	3 Months Ended
	Mar. 31, 2019USD ($)$ / sharesshares	Dec. 31, 2018shares
Noncontrolling Interests - Operating Partnership
Redemption value of the noncontrolling interest | $	$ 1.2
Closing price of the Company's stock (in dollars per share) | $ / shares	$ 107.02
Operating partnership
Noncontrolling Interests - Operating Partnership
Conversion ratio for common operating partnership units	1
Number of Operating Partnership Units (in shares)	47,984,605	47,831,300
Percentage of Total	100.00%	100.00%
Shares of common stock issued related to employee compensation arrangements	153,305
Quarterly distributions will receive by holders of operating partnership units (in dollars per unit) | $ / shares	$ 1.10
Operating partnership | Coresite Realty Corporation
Noncontrolling Interests - Operating Partnership
Number of Operating Partnership Units (in shares)	36,409,337	36,256,032
Percentage of Total	75.90%	75.80%
Operating partnership | Noncontrolling interests
Noncontrolling Interests - Operating Partnership
Number of Operating Partnership Units (in shares)	11,575,268	11,575,268
Percentage of Total	24.10%	24.20%

Equity Incentive Plan (Details)

Equity Incentive Plan (Details) - 2010 Plan - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Equity Incentive Plan
Shares of common stock reserved for issuance	6,000,000
Shares of common stock that were available for issuance	2,661,409
Stock Options
Number of Shares Subject to Option
Options outstanding at the beginning of the period (in shares)	49,133
Exercised (in shares)	(1,129)
Options outstanding at the end of the period (in shares)	48,004
Weighted Average Exercise Price
Options outstanding at the beginning of the period (in dollars per share)	$ 20.06
Exercised (in dollars per share)	15.23
Options outstanding at the end of the period (in dollars per share)	$ 20.17
Restricted Awards
Restricted Awards and PSA's
Unvested balance at the beginning of the period (in shares)	284,879
Granted (in shares)	147,881
Forfeited (in shares)	(1,698)
Vested (in shares)	(109,287)
Unvested balance at the end of the period (in shares)	321,775
Weighted Average Fair Value at Grant
Unvested balance at the beginning of the period (in dollars per share)	$ 85.98
Granted (in dollars per share)	100.38
Forfeited (in dollars per share)	88.05
Vested (in dollars per share)	77.73
Unvested balance at the end of the period (in dollars per share)	$ 95.39
Compensation cost not yet recognized
Unearned compensation	$ 28.8
Restricted Awards | Weighted Average
Compensation cost not yet recognized
Vesting period	2 years 10 months 24 days
PSAs
Compensation cost not yet recognized
Unearned compensation	$ 9.1
Assumptions used to value the stock options granted
Expected term	2 years 9 months 26 days	2 years 9 months 26 days
Expected volatility (as a percent)	24.09%	24.15%
Risk-free rate (as a percent)	2.48%	2.24%
PSAs | Weighted Average
Weighted Average Fair Value at Grant
Unvested balance at the beginning of the period (in dollars per share)	$ 96.58
Granted (in dollars per share)	114.55
Vested (in dollars per share)	84.78
Unvested balance at the end of the period (in dollars per share)	$ 107.69
Compensation cost not yet recognized
Vesting period	2 years 6 months
PSAs | Minimum
Restricted Awards and PSA's
Unvested balance at the beginning of the period (in shares)	50,823
Granted (in shares)	10,926
Performance adjustment	18,063
Vested (in shares)	(43,650)
Unvested balance at the end of the period (in shares)	36,162
Compensation cost not yet recognized
Percentage of target number of shares for PSAs granted in years 2015, 2016 and 2017	25.00%
Assumptions used to value the stock options granted
Performance period	1 year
PSAs | Maximum
Restricted Awards and PSA's
Unvested balance at the beginning of the period (in shares)	173,944
Granted (in shares)	76,480
Performance adjustment	(29,819)
Vested (in shares)	(43,650)
Unvested balance at the end of the period (in shares)	176,955
Compensation cost not yet recognized
Percentage of target number of shares for PSAs granted in years 2015, 2016 and 2017	175.00%
Assumptions used to value the stock options granted
Performance period	3 years
PSAs | Target
Restricted Awards and PSA's
Unvested balance at the beginning of the period (in shares)	112,385
Granted (in shares)	43,703
Performance adjustment	(5,878)
Vested (in shares)	(43,650)
Unvested balance at the end of the period (in shares)	106,560

Earnings Per Share (Details)

Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Earnings Per Share
Net income attributable to common shares	$ 19,661	$ 20,302
Weighted-average common shares outstanding - basic	36,347,781	33,935,564
Effect of potentially dilutive common shares:
Stock options	38,921	53,813
Unvested awards	160,363	174,858
Weighted-average common shares outstanding - diluted	36,547,065	34,164,235
Net income per share attributable to common shares
Basic (in dollars per share)	$ 0.54	$ 0.60
Diluted (in dollars per share)	$ 0.54	$ 0.59
Weighted-average potentially dilutive securities excluded in calculation of basic and diluted income (loss) per share	39,754	37,760

Estimated Fair Value of Finan_2

Estimated Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Estimated Fair Value of Financial Instruments
Total principal outstanding	$ 1,216,000	$ 1,136,500
Significant Unobservable Inputs (Level 3)
Estimated Fair Value of Financial Instruments
Fair value of debt	$ 1,217,700	$ 1,131,800

Commitments and Contingencies (

Commitments and Contingencies (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Mar. 31, 2019
Telecommunications Capacity
Commitments and Contingencies
Open commitments		$ 75.5
Telecommunications Capacity | Forecast
Commitments and Contingencies
Open commitments met	$ 7.4
Construction Contracts
Commitments and Contingencies
Open commitments		$ 188.7