Summary Of Significant Accounting Policies (Narrative) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended	9 Months Ended
Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012 D	Sep. 30, 2011	Dec. 31, 2011
Summary Of Significant Accounting Policies [Abstract]
Period in which short-term investment become cash equivalents (days)			90
Assets or liabilities for uncertain tax positions	$ 0		$ 0		$ 0
Interest or penalties from uncertain tax positions	0	0	0	0
Asset retirement obligations	1.7		1.7		1.2
Interest capitalized	4.5	4.8	13.6	13.6
Compensation costs, leasing and construction activities	8.0	6.5	23.3	18.8
Cash flows from capitalized leasing costs			$ 26.5	$ 19.1

The carrying amount of a liability for an asset retirement obligation. An asset retirement obligation is a legal obligation associated with the disposal or retirement of a tangible long-lived asset that results from the acquisition, construction or development, or the normal operations of a long-lived asset, except for certain obligations of lessees.

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This element represents the total of interest expense recognized for an underpayment of income taxes computed by applying the applicable statutory rate of interest to the difference between a tax position recognized for financial reporting purposes and the amount previously taken or expected to be taken in a tax return of the entity and the amount of statutory penalties in the period in which the entity claims or expects to claim a tax position, in its tax return, that does not meet the minimum statutory threshold to avoid payment of penalties.

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