Summary of Significant Accounting Policies (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Summary Of Significant Accounting Policies [Line Items]
Aggregate principal amount	$ 19,900
Payment of minimum tax withholdings related to equity based awards	4,725	$ 2,584	$ 1,088
Proceeds from exercise of stock options	$ 4,972	858	559
Useful life of property	40 years
Increase Decrease In Accounts Payable And Accrued Liabilities	$ (5,071)	6,290	9,467
Depreciation expense from operation	104,300	90,600	65,000
Real estate cost capitalized excluding interest cost	12,700	11,000	10,800
Real estate interest cost capitalized incurred	14,300	11,400	9,800
Qualitytech, LP
Summary Of Significant Accounting Policies [Line Items]
Payment of minimum tax withholdings related to equity based awards	4,725	2,584	1,088
Proceeds from exercise of stock options	4,972	858	559
Increase Decrease In Accounts Payable And Accrued Liabilities	(5,071)	6,290	9,467
Real Estate Assets
Summary Of Significant Accounting Policies [Line Items]
Depreciation expense from operation	90,100	77,500	55,200
Non-Real Estate Assets
Summary Of Significant Accounting Policies [Line Items]
Depreciation expense from operation	$ 14,200	13,100	9,800
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
Cash Inflows | Accounting Standards Update 2016-09 [Member]
Summary Of Significant Accounting Policies [Line Items]
Proceeds from exercise of stock options		$ 900	600
Increase Decrease In Accounts Payable And Accrued Liabilities			(600)
Cash Outflows | Accounting Standards Update 2016-09 [Member]
Summary Of Significant Accounting Policies [Line Items]
Payment of minimum tax withholdings related to equity based awards	$ 900		1,100
Increase Decrease In Accounts Payable And Accrued Liabilities			$ (1,100)
Term Loan Maturing 2022
Summary Of Significant Accounting Policies [Line Items]
Interest rate	5.875%
Aggregate principal amount	$ 300,000
Term Loan Maturing 2025
Summary Of Significant Accounting Policies [Line Items]
Interest rate	4.75%
Aggregate principal amount	$ 400,000