Organization (Details) (USD $) In Millions, except Share data, unless otherwise specified	0 Months Ended
	Sep. 28, 2010	Dec. 31, 2012 Operating partnership Entities that owned Predecessor	Dec. 31, 2012 Operating partnership Entities that owned CoreSite Acquired Properties	Dec. 31, 2012 Common Shares Operating partnership	Dec. 31, 2012 Common Shares Operating partnership Entities that owned Predecessor
Organization
Sale of common stock in initial public offering (in shares)	19,435,000
Price per share (in dollars per share)	$ 16.00
Net proceeds from initial public offering	$ 285.6
Organization
Percentage of ownership interests acquired		100.00%	100.00%
Percentage of ownership interests held by the entity				44.80%
Percentage of ownership interests held by noncontrolling owners					55.00%