Summary of Significant Accounting Policies (Narrative) (Details)	12 Months Ended
	Dec. 31, 2019 USD ($) category	Dec. 31, 2018 USD ($) category	Dec. 31, 2017 USD ($)
Summary Of Significant Accounting Policies [Line Items]
Operating assets independent of the Operating Partnership	$ 0
Maximum exposure to losses	$ 30,200,000
Number of Revenue Categories | category	4	2
Useful life of property	40 years
Depreciation expense from operation	$ 130,800,000	$ 113,500,000	$ 104,300,000
Real estate cost capitalized excluding interest cost	17,800,000	17,400,000	12,700,000
Real estate interest cost capitalized incurred	33,200,000	26,800,000	14,300,000
Gain on sale of real estate, net	14,769,000
Gain (loss) on disposition of property	14,769,000	(6,994,000)
Reclassification from Other Revenue to Rental Income [Member]
Summary Of Significant Accounting Policies [Line Items]
Prior Period Reclassification Adjustment		7,400,000	$ 6,100,000
Reclassification from Cloud and Managed Services to Other Revenue[Member]
Summary Of Significant Accounting Policies [Line Items]
Prior Period Reclassification Adjustment		35,700,000
Qualitytech, LP
Summary Of Significant Accounting Policies [Line Items]
Operating assets independent of the Operating Partnership	0
Gain on sale of real estate, net	14,769,000
Gain (loss) on disposition of property	$ 14,769,000	(6,994,000)
Term Loan Maturing 2025
Summary Of Significant Accounting Policies [Line Items]
Interest rate			4.75%
Senior Notes 4.75 Due 2025 [Member]
Summary Of Significant Accounting Policies [Line Items]
Interest rate	4.75%
Real Estate Assets
Summary Of Significant Accounting Policies [Line Items]
Depreciation expense from operation	$ 118,900,000	101,200,000	$ 90,100,000
Non-Real Estate Assets
Summary Of Significant Accounting Policies [Line Items]
Depreciation expense from operation	$ 11,900,000	12,300,000	14,200,000
Other | Reclassification from Cloud and Managed Services to Other Revenue[Member]
Summary Of Significant Accounting Policies [Line Items]
Prior Period Reclassification Adjustment			65,500,000
Other | Reclassification Other Revenue [Member]
Summary Of Significant Accounting Policies [Line Items]
Prior Period Reclassification Adjustment			1,200,000
Recoveries From Customers
Summary Of Significant Accounting Policies [Line Items]
Prior Period Reclassification Adjustment		45,400,000	$ 37,900,000
Minimum | Real Property
Summary Of Significant Accounting Policies [Line Items]
Useful life of property	20 years
Maximum | Real Property
Summary Of Significant Accounting Policies [Line Items]
Useful life of property	40 years
Maximum | Leasehold Improvements
Summary Of Significant Accounting Policies [Line Items]
Useful life of property	20 years
Maximum | Other | Reclassification Other Revenue [Member]
Summary Of Significant Accounting Policies [Line Items]
Prior Period Reclassification Adjustment		1,200,000
Restructuring Charges.
Summary Of Significant Accounting Policies [Line Items]
Gain (loss) on disposition of property		$ (7,000,000.0)
Atlanta Metro facility
Summary Of Significant Accounting Policies [Line Items]
Gain on sale of real estate, net	$ 1,400,000
Owned Properties | Manassas, Virginia
Summary Of Significant Accounting Policies [Line Items]
Transaction cost	5,800,000
Gain on sale of real estate, net	$ 13,400,000