Document and Entity Information	3 Months Ended
	Mar. 31, 2015	Apr. 22, 2015
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, 2015
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Accelerated Filer
Entity Common Stock, Shares Outstanding		22,019,669
Document Fiscal Year Focus	2015
Document Fiscal Period Focus	Q1