Summary of Significant Accounting Policies - (Basis of Presentation to Real Estate Assets) (Details)	3 Months Ended
	Mar. 31, 2020 USD ($) entity	Mar. 31, 2019 USD ($)	Nov. 08, 2017	Jul. 23, 2014
Summary Of Significant Accounting Policies [Line Items]
Operating assets independent of the Operating Partnership	$ 0
Number of unconsolidated entities considered as a VIE for which entity is not the primary beneficiary | entity	1
Maximum exposure to losses	$ 32,100,000
Depreciation expense from operation	35,700,000	$ 30,300,000
Real estate cost capitalized excluding interest cost	4,500,000	4,500,000
Real estate interest cost capitalized incurred	8,100,000	7,800,000
Gain on sale of real estate, net		13,408,000
Qualitytech, LP
Summary Of Significant Accounting Policies [Line Items]
Operating assets independent of the Operating Partnership	$ 0
Gain on sale of real estate, net		13,408,000
Real Property
Summary Of Significant Accounting Policies [Line Items]
Useful life of property	40 years
Real Estate Assets
Summary Of Significant Accounting Policies [Line Items]
Depreciation expense from operation	$ 32,300,000	27,400,000
Non-Real Estate Assets
Summary Of Significant Accounting Policies [Line Items]
Depreciation expense from operation	$ 3,400,000	2,900,000
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
Senior Notes
Summary Of Significant Accounting Policies [Line Items]
Interest rate	4.75%		4.75%	5.875%
Unconsolidated Affiliate [Member] | Manassas, Virginia
Summary Of Significant Accounting Policies [Line Items]
Gain on sale of real estate, net		13,400,000
Transaction cost		$ 5,800,000