Summary of Significant Accounting Policies (Narrative) (Details)	3 Months Ended								12 Months Ended
	Dec. 31, 2016 USD ($)	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Sep. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)	Mar. 31, 2015 USD ($)	Dec. 31, 2016 USD ($) segment	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Summary Of Significant Accounting Policies [Line Items]
Period in which short-term investment become cash equivalents									90 days
Goodwill	$ 752,970,000				$ 330,664,000				$ 752,970,000	$ 330,664,000
Interest capitalized									16,300,000	12,900,000	$ 20,400,000
Compensation costs, leasing and construction activities									68,900,000	56,800,000	50,100,000
Cash flows from capitalized leasing costs									47,300,000	49,900,000	49,000,000
Deferred leasing costs, net	253,700,000				236,000,000				253,700,000	236,000,000
Gain (loss) on cash flow hedge ineffectiveness									(3,100,000)	(1,600,000)	800,000
Assets or liabilities for uncertain tax positions	0				0				0	0
Interest or penalties from uncertain tax positions									0	0	0
Non-cash gain on lease termination	29,200,000								0	14,355,000	0
Asset retirement obligations	5,700,000				1,300,000				$ 5,700,000	1,300,000
Number of reportable segments | segment									1
Operating revenue	576,787,000	$ 546,293,000	$ 514,934,000	$ 504,199,000	500,443,000	$ 435,989,000	$ 420,295,000	$ 406,609,000	$ 2,142,213,000	1,763,336,000	1,616,438,000
Restricted cash	11,508,000				18,009,000				11,508,000	18,009,000
Global revolving credit facility
Summary Of Significant Accounting Policies [Line Items]
Deferred financing costs	10,900,000				7,600,000				10,900,000	7,600,000
Unsecured term loan
Summary Of Significant Accounting Policies [Line Items]
Deferred financing costs	6,100,000				1,300,000				$ 6,100,000	1,300,000
Accounting Standards Update 2015-03 [Member] | Deferred Financing Costs, Net
Summary Of Significant Accounting Policies [Line Items]
Deferred financing costs					(35,200,000)					(35,200,000)
Accounting Standards Update 2015-03 [Member] | Long-Term Line of Credit | Global revolving credit facility
Summary Of Significant Accounting Policies [Line Items]
Deferred financing costs					7,600,000					7,600,000
Accounting Standards Update 2015-03 [Member] | Long-Term Line of Credit | Unsecured term loan
Summary Of Significant Accounting Policies [Line Items]
Deferred financing costs					1,300,000					1,300,000
Accounting Standards Update 2015-03 [Member] | Unsecured Debt
Summary Of Significant Accounting Policies [Line Items]
Deferred financing costs					26,000,000					26,000,000
Accounting Standards Update 2015-03 [Member] | Secured Debt
Summary Of Significant Accounting Policies [Line Items]
Deferred financing costs					300,000					300,000
Minimum
Summary Of Significant Accounting Policies [Line Items]
MSA term									1 year
Maximum
Summary Of Significant Accounting Policies [Line Items]
MSA term									3 years
Buildings and improvements | Minimum
Summary Of Significant Accounting Policies [Line Items]
Building and improvements, useful life									5 years
Buildings and improvements | Maximum
Summary Of Significant Accounting Policies [Line Items]
Building and improvements, useful life									39 years
Machinery and equipment | Minimum
Summary Of Significant Accounting Policies [Line Items]
Building and improvements, useful life									7 years
Machinery and equipment | Maximum
Summary Of Significant Accounting Policies [Line Items]
Building and improvements, useful life									15 years
Furniture and Fixtures | Minimum
Summary Of Significant Accounting Policies [Line Items]
Building and improvements, useful life									3 years
Furniture and Fixtures | Maximum
Summary Of Significant Accounting Policies [Line Items]
Building and improvements, useful life									5 years
United States
Summary Of Significant Accounting Policies [Line Items]
Operating revenue									$ 1,700,000,000	1,400,000,000	1,200,000,000
Long-lived assets	6,300,000,000				6,100,000,000				6,300,000,000	6,100,000,000	5,400,000,000
Non-US
Summary Of Significant Accounting Policies [Line Items]
Operating revenue									400,000,000	400,000,000	400,000,000
Long-lived assets	2,600,000,000				2,600,000,000				2,600,000,000	2,600,000,000	2,700,000,000
United Kingdom
Summary Of Significant Accounting Policies [Line Items]
Operating revenue									200,000,000	200,000,000	200,000,000
Long-lived assets	$ 1,500,000,000				$ 1,600,000,000				$ 1,500,000,000	$ 1,600,000,000	$ 1,700,000,000
United Kingdom | Sales
Summary Of Significant Accounting Policies [Line Items]
Concentration risk									11.10%	12.30%	13.30%
United Kingdom | Long-Lived Assets
Summary Of Significant Accounting Policies [Line Items]
Concentration risk									16.60%	18.80%	21.30%