Long-Term Debt (Outstanding Long-Term Debt) (Details) (USD $)	Mar. 31, 2012		Dec. 31, 2011
Revolving Credit Facility	$ 0		$ 0
Capital leases	1,072,000		1,257,000
Total debt and capital lease obligations	797,488,000		797,574,000
Current portion of long-term debt	625,000		662,000	[1]
Long-term debt, less current portion	796,863,000		796,912,000	[1]
Senior Notes due 2021 at 4.875% [Member]
Senior notes	496,910,000	[2]	496,824,000
Senior notes, unamortized discount	3,100,000
Effective interest rate of the notes	4.945%
Senior Notes due 2021 at 4.625% [Member]
Senior notes	299,506,000	[3]	299,493,000
Senior notes, unamortized discount	$ 500,000
Effective interest rate of the notes	4.642%

[1] Note: The balance sheet at December 31, 2011, has been derived from the audited consolidated financial statements at that date, but does not include all of the information and footnotes required by accounting principles generally accepted in the United States for complete financial statements.

[2] Net of unamortized original issuance discount of $3.1 million

[3] Net of unamortized original issuance discount of $0.5 million