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Senior Notes (Details) (USD $)	12 Months Ended
	Dec. 31, 2013 senior_note	Dec. 31, 2012	Dec. 31, 2013 2022 Senior Notes [Member]	Dec. 31, 2013 2042 Senior Notes [Member]	Feb. 11, 2014 2024 Senior Notes [Member] Subsequent Event [Member]
Debt Disclosure [Abstract]
Number of senior notes outstanding	2
Deb Instrument [Line Items]
Par value	$ 730,800,000	$ 730,800,000	$ 140,000,000	$ 200,000,000	$ 400,000,000.0
Interest rate			5.25%	6.375%	4.25%

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- Definition

Represents the number of debt instruments outstanding during the period.

+ References

No definition available.

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- Definition

Face (par) amount of debt instrument at time of issuance.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 835

-SubTopic 30

-Section 45

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6451184&loc=d3e28551-108399



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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 835

-SubTopic 30

-Section 55

-Paragraph 8

-URI http://asc.fasb.org/extlink&oid=6584090&loc=d3e28878-108400

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- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

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

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