Summary of Significant Accounting Policies (Narrative) (Details)	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2016 USD ($)	Jun. 30, 2015 USD ($)	Jun. 30, 2016 USD ($) segment	Jun. 30, 2015 USD ($)	Dec. 31, 2015 USD ($)
Summary Of Significant Accounting Policies [Line Items]
Period in which short-term investment become cash equivalents			90 days
Interest capitalized	$ 3,900,000	$ 3,200,000	$ 7,700,000	$ 7,500,000
Compensation costs, leasing and construction activities	16,400,000	12,400,000	34,100,000	25,900,000
Cash flows from capitalized leasing costs			21,300,000	26,400,000
Goodwill	330,664,000		$ 330,664,000		$ 330,664,000
Award vesting period			4 years
Unrecognized tax benefits	0		$ 0		0
Income tax penalties and interest expense	0	0	$ 0	0
Number of reportable segments | segment			1
Total operating revenues	514,934,000	420,295,000	$ 1,019,133,000	826,904,000
Rental property operating and maintenance	159,548,000	129,539,000	313,717,000	254,102,000
Global revolving credit facility
Summary Of Significant Accounting Policies [Line Items]
Deferred financing costs	12,500,000		12,500,000		7,600,000
Unsecured term loan
Summary Of Significant Accounting Policies [Line Items]
Deferred financing costs	$ 6,800,000		$ 6,800,000		1,300,000
Accounting Standards Update 2015-03 | Deferred Financing Costs, Net
Summary Of Significant Accounting Policies [Line Items]
Deferred financing costs					(35,200,000)
Accounting Standards Update 2015-03 | Long-Term Line of Credit | Global revolving credit facility
Summary Of Significant Accounting Policies [Line Items]
Deferred financing costs					7,600,000
Accounting Standards Update 2015-03 | Long-Term Line of Credit | Unsecured term loan
Summary Of Significant Accounting Policies [Line Items]
Deferred financing costs					1,300,000
Accounting Standards Update 2015-03 | Unsecured Debt
Summary Of Significant Accounting Policies [Line Items]
Deferred financing costs					26,000,000
Accounting Standards Update 2015-03 | Secured Debt
Summary Of Significant Accounting Policies [Line Items]
Deferred financing costs					$ 300,000
Restatement Adjustment
Summary Of Significant Accounting Policies [Line Items]
Rental property operating and maintenance		$ (1,500,000)		$ (2,800,000)
Sales
Summary Of Significant Accounting Policies [Line Items]
Concentration risk	10.10%	13.00%	10.10%	12.70%
Long-Lived Assets
Summary Of Significant Accounting Policies [Line Items]
Concentration risk			17.20%		18.80%
Outside The United States
Summary Of Significant Accounting Policies [Line Items]
Total operating revenues	$ 101,400,000	$ 97,900,000	$ 199,300,000	$ 189,800,000
Long-lived assets	2,500,000,000		2,500,000,000		$ 2,600,000,000
United States
Summary Of Significant Accounting Policies [Line Items]
Total operating revenues	413,500,000	322,400,000	819,800,000	637,100,000
Long-lived assets	6,100,000,000		6,100,000,000		6,000,000,000
United Kingdom
Summary Of Significant Accounting Policies [Line Items]
Total operating revenues	51,800,000	$ 54,800,000	103,400,000	$ 104,900,000
Long-lived assets	$ 1,500,000,000		$ 1,500,000,000		$ 1,600,000,000