Long-Term Debt (Outstanding Long-Term Debt) (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Revolving Credit Facility	$ 0	$ 0
Capital leases	114	322
Total debt and capital lease obligations	1,396,099	1,095,956
Current portion of long-term debt	68	222	[1]
Long-term debt, less current portion	1,396,031	1,095,734	[1]
Senior Notes due 2021 at 4.875% [Member]
Senior notes	497,437	497,173
Senior notes, unamortized discount	2,600	2,800
Effective interest rate of the notes	4.971%
Senior Notes due 2021 at 4.625% [Member]
Senior notes	299,585	299,545
Senior notes, unamortized discount	400	500
Effective interest rate of the notes	4.649%
Senior Notes due 2022 at 3.800% [Member]
Senior notes	298,987	298,916
Senior notes, unamortized discount	1,000	1,100
Effective interest rate of the notes	3.845%
Senior Notes due 2023 at 3.850% [Member]
Senior notes	299,976	0
Senior notes, unamortized discount	$ 23
Effective interest rate of the notes	3.851%

[1] The balance sheet at December 31, 2012, 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.