Noncontrolling Interests - Operating Partnership (Details) $ / shares in Units, $ in Thousands		9 Months Ended	12 Months Ended
	Dec. 12, 2012 shares	Sep. 30, 2017 USD ($) $ / shares shares	Dec. 31, 2016 shares
Noncontrolling Interests - Operating Partnership
Series A Cumulative Preferred Stock, dividend rate (as a percent)		7.25%	7.25%
Closing price of the Company's stock (in dollars per share) | $ / shares		$ 111.90
Noncontrolling Interests
Noncontrolling Interests - Operating Partnership
Reduction to noncontrolling interests in the Operating Partnership and an increase to common stock and additional paid in capital | $		$ 167
Operating partnership
Noncontrolling Interests - Operating Partnership
Conversion ratio for common operating partnership units		1
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%
Number of Operating Partnership Units (in shares)		47,661,165	47,227,915
Percentage of Total		71.00%
Percentage of Total		29.00%
Percentage of Total		100.00%	100.00%
Shares of common stock issued related to employee compensation arrangements		448,261
Quarterly distributions will receive by holders of operating partnership units (in dollars per unit) | $ / shares		$ 0.90
Operating partnership | Coresite Realty Corporation
Noncontrolling Interests - Operating Partnership
Number of Operating Partnership Units (in shares)		33,824,829	33,376,568
Percentage of Total		71.00%	70.70%
Operating partnership | Noncontrolling Interests
Noncontrolling Interests - Operating Partnership
Number of Operating Partnership Units (in shares)		13,836,336	13,851,347
Percentage of Total		29.00%	29.30%
Redemption value of the noncontrolling interests | $		$ 1,500,000