Long Term Debt (Details Textual)	12 Months Ended
Dec. 31, 2011
Long Term Debt (Textual) [Abstract]
Notice period for redemption of notes	15 to 60 days
5.70% Senior Notes [Member]
Long Term Debt (Textual) [Abstract]
Interest rate of senior notes	5.70%
5.875% Senior Notes [Member]
Long Term Debt (Textual) [Abstract]
Interest rate of senior notes	5.875%
4.875% Senior Notes [Member]
Long Term Debt (Textual) [Abstract]
Interest rate of senior notes	4.875%
5.15% Senior Notes [Member]
Long Term Debt (Textual) [Abstract]
Interest rate of senior notes	5.15%

Interest rate stated in the contractual debt agreement.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 22

-Article 5

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.22(a)(1))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Name:	us-gaap_DebtInstrumentInterestRateStatedPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant