Debt (Schedule of Long-Term Debt) (Details) (USD $)	6 Months Ended
Jun. 30, 2014	Dec. 31, 2013
Debt Instrument [Line Items]
Capital lease obligations	$ 169,200,000	$ 126,000,000
Total debt	1,165,600,000	816,800,000
Less current maturities	(76,914,000)	(51,376,000)
Long-term debt	1,088,666,000	765,425,000
Capital Lease Obligations [Member]
Debt Instrument [Line Items]
Lease expiration date, range, end	Jun. 13, 2021
Notes Payable [Member] \| Equipment [Member]
Debt Instrument [Line Items]
Carrying value of debt	52,500,000	26,900,000
Debt instrument, maturity date, range, end	May 01, 2018
Unsecured Debt [Member] \| 2011 4.0% Notes [Member]
Debt Instrument [Line Items]
Debt instrument, maturity date	Jun. 15, 2014
Unsecured Debt [Member] \| 2009 4.0% Notes [Member]
Debt Instrument [Line Items]
Debt instrument, maturity date	Jun. 15, 2014
Unsecured Debt [Member] \| 4.875% Senior Notes [Member] \| Senior Notes [Member]
Debt Instrument [Line Items]
Debt instrument, maturity date	Mar. 15, 2023
Carrying value of debt	400,000,000	400,000,000
Unsecured Debt [Member] \| 2011 4.0% Notes [Member] \| Convertible Debt [Member]
Debt Instrument [Line Items]
Carrying value of debt	0	103,800,000
Unsecured Debt [Member] \| 2011 4.25% Notes [Member] \| Convertible Debt [Member]
Debt Instrument [Line Items]
Debt instrument, maturity date	Dec. 15, 2014
Carrying value of debt	95,700,000	94,500,000
Unsecured Debt [Member] \| 2009 4.0% Notes [Member] \| Convertible Debt [Member]
Debt Instrument [Line Items]
Carrying value of debt	0	9,600,000
Unsecured Debt [Member] \| 2009 4.25% Notes [Member] \| Convertible Debt [Member]
Debt Instrument [Line Items]
Debt instrument, maturity date	Dec. 15, 2014
Carrying value of debt	3,000,000	3,000,000
Credit Facility [Member]
Debt Instrument [Line Items]
Line of credit facility, maturity date	Oct. 29, 2018
Credit Facility [Member] \| Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Credit facility, amount outstanding	398,400,000	53,000,000
Other Credit Facilities [Member]
Debt Instrument [Line Items]
Line of credit facility, maturity date	Mar. 03, 2015
Other Credit Facilities [Member] \| Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Credit facility, amount outstanding	$ 46,800,000	$ 0

Amount equal to the present value (the principal) at the beginning of the lease term of minimum lease payments during the lease term (excluding that portion of the payments representing executory costs such as insurance, maintenance, and taxes to be paid by the lessor, together with any profit thereon) net of payments or other amounts applied to the principal through the balance sheet date.

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- Definition

Sum of the carrying values as of the balance sheet date of all debt, including all short-term borrowings, long-term debt, and capital lease obligations.

+ References

Reference 1: 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)

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-Publisher FASB

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-Topic 942

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- Definition

Date when the debt instrument is scheduled to be fully repaid, in CCYY-MM-DD format.

+ 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

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-Topic 210

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-Subparagraph (SX 210.5-02.22(a)(2))

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- Definition

Latest date the outstanding debt instruments are required to be repaid, in CCYY-MM-DD format.

+ References

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- Definition

Date which lease or group of leases is set to expire, in CCYY-MM-DD format.

+ References

No definition available.

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- Definition

Amount borrowed under the credit facility as of the balance sheet date.

+ References

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-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 19, 22

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- Definition

Date the credit facility terminates, in CCYY-MM-DD format.

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

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- Definition

Carrying amount of long-term debt, net of unamortized discount or premium, including current and noncurrent amounts. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

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- Definition

Amount of long-term debt and capital lease obligation due after one year or beyond the normal operating cycle, if longer.

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-Name Regulation S-X (SX)

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-Name Staff Accounting Bulletin (SAB)

-Number Topic 6

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Amount of long-term debt and capital leases due within one year or the normal operating cycle, if longer.

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