Acquisitions (Narrative) (Details) $ in Millions			12 Months Ended
	Oct. 06, 2017 USD ($) ft² MW	Dec. 16, 2016 USD ($) MW	Dec. 31, 2018 USD ($)	Dec. 16, 2016 ft²	Dec. 16, 2016 a	Jun. 06, 2016 ft² a MW
Fort Worth Facility
Business Acquisition [Line Items]
Acquisition costs | $		$ 50.1
Area of facility (in square feet)				262,000	53
Capacity of the plant (in MW) | MW		50
Fort Worth Facility | Basis Of Design [Member]
Business Acquisition [Line Items]
Area of facility (in square feet)				80,000
Piscataway Facility
Business Acquisition [Line Items]
Acres of real estate property | a						38
Area of facility (in square feet)						360,000
Piscataway Facility | Raised Floor With 18 MW of Critical Power
Business Acquisition [Line Items]
Area of facility (in square feet)						89,000
Capacity of the plant (in MW) | MW						18
Piscataway Facility | Additional Raised Floor With 8 MW of Additional Critical Power
Business Acquisition [Line Items]
Area of facility (in square feet)						87,000
Capacity of the plant (in MW) | MW						8
Carpathia Hosting, Inc.
Business Acquisition [Line Items]
Capital Lease Obligations Incurred | $			$ 0.3
Vault Campus In Dulles Virginia [Member] [Member]
Business Acquisition [Line Items]
Area of facility (in square feet)	87,000
Capital Lease Obligations Incurred | $	$ 17.8
Payments to Acquire Land | $	34.1
Net purchase price | $	$ 16.3
Vault Campus In Dulles Virginia [Member] [Member] | Raised Floor With Thirteen Mw Of Critical Power [Member]
Business Acquisition [Line Items]
Area of facility (in square feet)	31,000
Capacity of the plant (in MW) | MW	13