Summary Of Significant Accounting Policies (Narrative) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011 years	Dec. 31, 2010	Dec. 31, 2009
Summary Of Significant Accounting Policies [Abstract]
Interest cost capitalized	$ 0.4	$ 0.4	$ 0.2
Initial lease term of deferred lease, years	five
Deferred lease costs	5.1	4.7	4.0
Amortization expense	4.6	3.6	3.3
Unamortized deferred lease costs	9.9	9.4
Economic useful life of intangibles, years	15
Long-lived asset impairment charge	5.5	5.9	3.9
Asset retirement obligation	$ 5.4	$ 5.2