Summary of Significant Accounting Policies (Narrative) (Details)	3 Months Ended		12 Months Ended
	Mar. 31, 2016 USD ($) segment	Mar. 31, 2015 USD ($)	Dec. 31, 2015 USD ($)
Summary Of Significant Accounting Policies [Line Items]
Period in which short-term investment become cash equivalents (in days)	90 days
Interest capitalized	$ 3,800,000	$ 4,300,000
Compensation costs, leasing and construction activities	16,700,000	12,300,000
Cash flows from capitalized leasing costs	10,400,000	13,700,000
Goodwill	$ 330,664,000		$ 330,664,000
Award vesting period	4 years
Unrecognized tax benefits	$ 0		0
Income tax penalties and interest expense	$ 0	0
Number of reportable segments | segment	1
Total operating revenues	$ 504,199,000	406,609,000
Rental property operating and maintenance	154,169,000	124,563,000
Restatement Adjustment
Summary Of Significant Accounting Policies [Line Items]
Rental property operating and maintenance		$ (1,400,000)
Global revolving credit facility
Summary Of Significant Accounting Policies [Line Items]
Deferred financing costs	13,300,000		7,600,000
Unsecured term loan
Summary Of Significant Accounting Policies [Line Items]
Deferred financing costs	$ 7,200,000		$ 1,300,000
Sales
Summary Of Significant Accounting Policies [Line Items]
Concentration risk (as a percent)	10.20%	12.30%
Long-Lived Assets
Summary Of Significant Accounting Policies [Line Items]
Concentration risk (as a percent)	18.10%		18.80%
Outside The United States
Summary Of Significant Accounting Policies [Line Items]
Total operating revenues	$ 97,900,000	$ 92,000,000
Long-lived assets	2,700,000,000		$ 2,600,000,000
United States
Summary Of Significant Accounting Policies [Line Items]
Total operating revenues	406,300,000	314,700,000
Long-lived assets	6,100,000,000		6,000,000,000
United Kingdom
Summary Of Significant Accounting Policies [Line Items]
Total operating revenues	51,600,000	$ 50,000,000
Long-lived assets	1,600,000,000		$ 1,600,000,000
Deferred Financing Costs, Net | Accounting Standards Update 2015-03
Summary Of Significant Accounting Policies [Line Items]
Deferred financing costs	(35,200,000)
Long-Term Line of Credit | Global revolving credit facility | Accounting Standards Update 2015-03
Summary Of Significant Accounting Policies [Line Items]
Deferred financing costs	7,600,000
Long-Term Line of Credit | Unsecured term loan | Accounting Standards Update 2015-03
Summary Of Significant Accounting Policies [Line Items]
Deferred financing costs	1,300,000
Unsecured Debt | Accounting Standards Update 2015-03
Summary Of Significant Accounting Policies [Line Items]
Deferred financing costs	26,000,000
Secured Debt | Accounting Standards Update 2015-03
Summary Of Significant Accounting Policies [Line Items]
Deferred financing costs	$ 300,000