Summary Of Significant Accounting Policies (Narrative) (Details) (USD $)	3 Months Ended		6 Months Ended			3 Months Ended		6 Months Ended			3 Months Ended		6 Months Ended			3 Months Ended		6 Months Ended			3 Months Ended		6 Months Ended			12 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013 segment	Jun. 30, 2012	Dec. 31, 2012	Jun. 30, 2013 United States [Member]	Jun. 30, 2012 United States [Member]	Jun. 30, 2013 United States [Member]	Jun. 30, 2012 United States [Member]	Dec. 31, 2012 United States [Member]	Jun. 30, 2013 Outside The United States [Member]	Jun. 30, 2012 Outside The United States [Member]	Jun. 30, 2013 Outside The United States [Member]	Jun. 30, 2012 Outside The United States [Member]	Dec. 31, 2012 Outside The United States [Member]	Jun. 30, 2013 England [Member]	Jun. 30, 2012 England [Member]	Jun. 30, 2013 England [Member]	Jun. 30, 2012 England [Member]	Dec. 31, 2012 England [Member]	Jun. 30, 2013 Sales [Member] England [Member]	Jun. 30, 2012 Sales [Member] England [Member]	Jun. 30, 2013 Sales [Member] England [Member]	Jun. 30, 2012 Sales [Member] England [Member]	Jun. 30, 2013 Long-Lived Assets [Member] England [Member]	Dec. 31, 2012 Long-Lived Assets [Member] England [Member]
Summary Of Significant Accounting Policies [Line Items]
Period in which short-term investment become cash equivalents			90 days
Interest capitalized	$ 6,600,000	$ 4,600,000	$ 12,000,000	$ 9,100,000
Compensation costs, leasing and construction activities	9,600,000	7,400,000	19,700,000	15,300,000
Cash flows from capitalized leasing costs			21,000,000	14,700,000
Assets or liabilities for uncertain tax positions	0		0		0
Interest or penalties from uncertain tax positions	0	0	0	0
Asset retirement obligations	1,700,000		1,700,000		1,700,000
Number of reportable segments			1
Total operating revenues	363,502,000	303,704,000	721,872,000	586,852,000		276,900,000	263,200,000	550,900,000	508,200,000		86,600,000	40,500,000	171,000,000	78,700,000		48,600,000	12,600,000	95,900,000	24,800,000
Long-lived assets						$ 5,500,000,000		$ 5,500,000,000		$ 5,000,000,000	$ 2,400,000,000		$ 2,400,000,000		$ 2,500,000,000	$ 1,600,000,000		$ 1,600,000,000		$ 1,700,000,000
Concentration risk																					13.40%	4.10%	13.30%	4.20%	20.00%	22.30%