Noncontrolling Interests - Operating Partnership (Details) (USD $) In Millions, except Share data, unless otherwise specified	0 Months Ended	3 Months Ended			12 Months Ended
	Dec. 12, 2012	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2013	Dec. 31, 2012
Noncontrolling Interests - Operating Partnership
Conversion ratio for common operating partnership units					1
Noncontrolling Interests Operating Partnership
Number of Units (in shares)					46,257,532	45,964,232
Percentage of Total					100.00%	100.00%
Shares of common stock issued related to employee compensation arrangements					286,964
Common Operating Partnership units issued to employees upon their vesting in the incentive unit awards (in shares)					7,138
Quarterly distributions received by holders of operating partnership units (in dollars per unit)		$ 0.27	$ 0.27	$ 0.27	$ 0.35
Preferred Operating Partnership units issued to CoreSite Realty Corporation (in shares)	4,600,000
Redemption value of the noncontrolling interests					$ 816.4
Closing price of the Company's stock (in dollars per share)					$ 32.19
The Company
Noncontrolling Interests Operating Partnership
Number of Units (in shares)					20,896,685	20,610,523
Percentage of Total					45.20%	44.80%
Common units held by third parties
Noncontrolling Interests Operating Partnership
Number of Units (in shares)					25,275,390	25,275,390
Percentage of Total					54.60%	55.00%
Incentive units held by employees
Noncontrolling Interests Operating Partnership
Number of Units (in shares)					85,457	78,319
Percentage of Total					0.20%	0.20%