Long-Term Debt (Outstanding Long-Term Debt) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Revolving Credit Facility	$ 0	$ 0
Capital leases	80	98
Total debt and capital lease obligation	1,396,316	1,396,208
Current portion of long-term debt	74	67	[1]
Long-term debt, less current portion	1,396,242	1,396,141	[1]
Senior Notes due 2021 at 4.875% [Member]
Senior notes	497,613	497,525
Senior notes, unamortized discount	2,400	2,500
Effective interest rate	4.969%
Senior Notes due 2021 at 4.625% [Member]
Senior notes	299,611	299,598
Senior notes, unamortized discount	400	400
Effective interest rate	4.648%
Senior Notes due 2022 at 3.800% [Member]
Senior notes	299,035	299,011
Senior notes, unamortized discount	1,000	1,000
Effective interest rate	3.845%
Senior Notes due 2023 at 3.850% [Member]
Senior notes	299,977	299,976
Senior notes, unamortized discount	$ 22	$ 23
Effective interest rate	3.851%

[1] The balance sheet at December 31, 2013, 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.