v3.19.3
Document and Entity Information - shares
9 Months Ended
Sep. 30, 2019
Oct. 30, 2019
Document and Entity Information    
Document Type 10-Q  
Document Quarterly Report true  
Document Transition Report false  
Document Period End Date Sep. 30, 2019  
Entity File Number 001-34877  
Entity Registrant Name CoreSite Realty Corp  
Entity Incorporation, State or Country Code MD  
Entity Tax Identification Number 27-1925611  
Entity Address, Address Line One 1001 17th Street, Suite 500  
Entity Address, City or Town Denver  
Entity Address, State or Province CO  
Entity Address, Postal Zip Code 80202  
City Area Code 866  
Local Phone Number 777-2673  
Title of 12(b) Security Common Stock, $0.01 par value per share  
Trading Symbol COR  
Security Exchange Name NYSE  
Entity Current Reporting Status Yes  
Entity Interactive Data Current Yes  
Entity Filer Category Large Accelerated Filer  
Entity Small Business false  
Entity Emerging Growth Company false  
Entity Shell Company false  
Entity Common Stock, Shares Outstanding   37,687,013
Current Fiscal Year End Date --12-31  
Document Fiscal Year Focus 2019  
Document Fiscal Period Focus Q3  
Entity Central Index Key 0001490892  
Amendment Flag false