Formation and Recent Developments - Narrative (Details) - USD ($) $ / shares in Units, shares in Millions									1 Months Ended					3 Months Ended		9 Months Ended
	Aug. 15, 2016	Aug. 10, 2016	Jul. 01, 2016	Mar. 31, 2016	Mar. 21, 2016	Dec. 31, 2015	Dec. 14, 2015	Jan. 24, 2013	Aug. 31, 2016	Mar. 31, 2016	Jun. 30, 2015	Apr. 30, 2015	Jun. 30, 2014	Sep. 30, 2016	Mar. 31, 2016	Sep. 30, 2016	Sep. 30, 2015	Mar. 17, 2016	Jan. 23, 2013
Business Formation [Line Items]
Proceeds from public stock offerings															$ 256,000,000	$ 448,600,000	$ 799,300,000
Tax payment upon exercise of equity awards (in shares)															0.9
Stock issued for ESPP (in shares)															0.1
Maximum proceeds from issuance of common stock			$ 320,000,000
Stock issuance costs																$ 1,600,000	$ 800,000
Second Amendment to Credit Agreement | Revolving credit facility
Business Formation [Line Items]
Optional additional borrowing capacity																		$ 250,000,000
Term Loan | Second Amendment to Credit Agreement
Business Formation [Line Items]
Optional additional borrowing capacity																		$ 250,000,000
The Company
Business Formation [Line Items]
Operating partnership units (in shares)														83.5		83.5	66.3
CyrusOne Inc. And CyrusOne GP
Business Formation [Line Items]
Shares purchased of Operating partnership's units (in shares)								21.9
Combined interest held on completion of transactions								33.90%
Purchase of Operating partnership's units								$ 337,100,000
Cincinnati Bell Inc.
Business Formation [Line Items]
Percentage of operating partnership's units held prior to IPO																			100.00%
Remaining combined interest held								66.10%
Ownership %						9.50%								5.00%		5.00%
IPO
Business Formation [Line Items]
Issuance of common stock (in shares)								19.0
Net proceeds from IPO after underwriting discounts								$ 337,100,000
Public stock offering
Business Formation [Line Items]
Issuance of common stock (in shares)	3.4				6.9	6.3	1.4		3.4	6.9	13.0	14.3	16.0
Proceeds from public stock offerings	$ 164,800,000				$ 255,000,000		$ 0		$ 164,800,000	$ 255,000,000	$ 373,300,000	$ 426,000,000	$ 355,900,000
Stock issuance costs	$ 6,900,000				$ 10,600,000
Public stock offering | Goldman, Sachs & Co.
Business Formation [Line Items]
Issuance of common stock (in shares)	4.4
Stock issued price (in dollars per share)		$ 48.48
Sales Agreements
Business Formation [Line Items]
Issuance of common stock (in shares)														0.5
Proceeds from public stock offerings														$ 26,300,000
Stock issuance costs														$ 300,000
Stock issued upon underwriters exercising option to purchase additional shares
Business Formation [Line Items]
Issuance of common stock (in shares)		1.0
CME Group's Data Center
Business Formation [Line Items]
Proceeds used to acquire the Chicago-Aurora I data center				$ 131,100,000