Fair Value Measurements (Schedule Of Fair Value Of Senior Notes) (Details) (USD $)	Mar. 31, 2012	Dec. 31, 2011	Mar. 26, 2011
Senior Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Aggregate principal amount of senior notes	$ 400,000,000
Senior Secured Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Aggregate principal amount of senior notes	250,000,000
Carrying Value [Member] | Senior Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
$400 million senior notes	150,027,000	399,953,000	400,032,000
Carrying Value [Member] | Senior Secured Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
$250 million senior secured notes	250,000,000
Fair Value [Member] | Senior Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
$400 million senior notes	155,637,000	381,067,000	404,800,000
Fair Value [Member] | Senior Secured Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
$250 million senior secured notes	$ 259,379,000