Noncontrolling Interests - Operating Partnership (Details) $ / shares in Units, $ in Millions		3 Months Ended			12 Months Ended
	Dec. 12, 2012 shares	Sep. 30, 2015 $ / shares	Jun. 30, 2015 $ / shares	Mar. 31, 2015 $ / shares	Dec. 31, 2015 USD ($) $ / shares shares	Dec. 31, 2014 shares
Noncontrolling Interests Operating Partnership
Conversion ratio for common operating partnership units					1
Number of Units (in shares)					46,994,903	46,648,038
Common Stock, shares issued					30,650,703	21,757,366
Percentage of Total					100.00%	100.00%
Shares of common stock issued related to employee compensation arrangements					349,365
Quarterly distributions will receive by holders of operating partnership units (in dollars per unit) | $ / shares		$ 0.42	$ 0.42	$ 0.42	$ 0.53
Carrying value of the noncontrolling interests | $					$ 110.2
Closing price of the Company's stock (in dollars per share) | $ / shares					$ 56.72
Preferred Operating Partnership units issued to CoreSite Realty Corporation (in shares)	4,600,000
Series A Cumulative Preferred Stock, dividend rate (as a percent)	7.25%				7.25%	7.25%
CoreSite Realty Corporation
Noncontrolling Interests Operating Partnership
Number of Units (in shares)					30,136,556	21,287,191
Percentage of Total					64.10%	45.60%
Noncontrolling Interests
Noncontrolling Interests Operating Partnership
Number of Units (in shares)					16,858,347	25,360,847
Percentage of Total					35.90%	54.40%
Redemption value of the noncontrolling interests | $					$ 956.2
Noncontrolling Interest Common Units Held by Third Parties
Noncontrolling Interests Operating Partnership
Number of Units (in shares)					8,500,000