Summary of Significant Accounting Policies (Narrative) (Details)	3 Months Ended		12 Months Ended
	Mar. 31, 2019 USD ($) category item	Mar. 31, 2018 USD ($) category	Dec. 31, 2018 USD ($)	Jul. 23, 2014
Summary Of Significant Accounting Policies [Line Items]
Interest rate				5.875%
Operating assets independent of the Operating Partnership	$ 0
Maximum exposure to losses	$ 44,000,000
Number of Revenue Categories | category	3	4
Rental	$ 98,596,000	$ 88,415,000
Useful life of property	40 years
Depreciation expense from operation	$ 30,300,000	26,900,000
Real estate cost capitalized excluding interest cost	4,500,000	3,500,000
Real estate interest cost capitalized incurred	7,800,000	5,400,000
Transaction cost	5,800,000
Gain on sale of real estate, net	13,408,000
Impairment losses	$ 0
Number of reporting units | item	1
Reclassification from Other Revenue to Rental Income [Member]
Summary Of Significant Accounting Policies [Line Items]
Prior Period Reclassification Adjustment		2,700,000
Qualitytech, LP
Summary Of Significant Accounting Policies [Line Items]
Operating assets independent of the Operating Partnership	$ 0
Rental	98,596,000	88,415,000
Gain on sale of real estate, net	$ 13,408,000
Term Loan Maturing 2025
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	$ 27,400,000	23,700,000
Non-Real Estate Assets
Summary Of Significant Accounting Policies [Line Items]
Depreciation expense from operation	$ 2,900,000	3,200,000
Other | Reclassification from Cloud and Managed Services to Other Revenue[Member]
Summary Of Significant Accounting Policies [Line Items]
Prior Period Reclassification Adjustment		13,200,000
Other | Reclassification Other Revenue [Member]
Summary Of Significant Accounting Policies [Line Items]
Prior Period Reclassification Adjustment		$ 600,000
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
Restructuring Charges [Member]
Summary Of Significant Accounting Policies [Line Items]
Impairment losses			$ 4,000,000