Debt - Convertible Bond Hedge, Warrant Transactions (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	6 Months Ended
Jun. 30, 2018	Feb. 11, 2014
Debt Instrument [Line Items]
Exercise price (in dollars per share)	$ 27.09
Initial exercise price (in dollars per share)	$ 34.12
Exercise price above last reported sale price of common stock	70.00%
Sale price of common stock (in dollars per share)		$ 20.07
Bond Option
Debt Instrument [Line Items]
Common stock covered under convertible bond hedge/warrants (in shares)	0.8
Warrants
Debt Instrument [Line Items]
Common stock covered under convertible bond hedge/warrants (in shares)	1.0
Convertible Notes due 2019 \| Convertible Debt
Debt Instrument [Line Items]
Amount of hedged item	$ 21.4

Represents the percentage of exercise price above last reported sale price of the entity's common stock.

No definition available.

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- Definition

Exercise price per share or per unit of warrants or rights outstanding.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(i)(4))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

+ Details

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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- Definition

Amount of hedged item in hedging relationship. Excludes hedged asset or liability.

+ References

No definition available.

+ Details

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Balance Type:	na
Period Type:	instant

- Definition

The number of issuer's shares to which the option contract is indexed.

+ References

+ Details

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Period Type:	instant

- Definition

Exercise or strike price stated in the contract for options indexed to the issuer's equity shares.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 40
-Section 50
-Paragraph 5
-Subparagraph (a)(2)
-URI http://asc.fasb.org/extlink&oid=6445032&loc=d3e90205-114008

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 480
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (f)(1)
-URI http://asc.fasb.org/extlink&oid=109262807&loc=d3e22047-110879

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- Definition

Price of a single share of a number of saleable stocks of a company.

+ References

No definition available.

+ Details

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- Details

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- Details

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- Details

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