Long Term Debt (Details) (USD $) In Thousands	Jun. 30, 2011	Dec. 31, 2010
Long-Term Debt
Total	$ 1,495,707	$ 1,495,593
5.15% Senior Notes (due 2014) [Member]
Long-Term Debt
Senior notes	249,778	249,745
4.875% Senior Notes (due 2015) [Member]
Long-Term Debt
Senior notes	249,751	249,724
5.875% Senior Notes (due 2019) [Member]
Long-Term Debt
Senior notes	499,382	499,351
5.70% Senior Notes (due 2039) [Member]
Long-Term Debt
Senior notes	$ 496,796	$ 496,773

Including the current and noncurrent portions, carrying value as of the balance sheet date of Notes with the highest claim on the assets of the issuer in case of bankruptcy or liquidation (with maturities initially due after one year or beyond the operating cycle if longer). Senior note holders are paid off in full before any payments are made to junior note holders.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 03
-Paragraph 16
-Article 9

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.16)
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.16(a))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Name:	us-gaap_SeniorNotes
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant