Long-Term Debt (Schedule Of Long-term Debt Instruments) (Details) (USD $) In Thousands	Jun. 30, 2011	Dec. 31, 2010
Credit facility
Senior notes	72,000	72,000
Long-term debt including current and non-current	722,000	722,000
Less current maturities	(18,000)	(18,000)
Total long-term debt	704,000	704,000
Series A [Member]
Senior notes	205,000	205,000
Series B [Member]
Senior notes	145,000	145,000
Term Loan [Member]
Long-term debt including current and non-current	$ 300,000	$ 300,000