Debt - Convertible Bond Hedge, Warrant Transactions (Details) - USD ($) $ / shares in Units, $ in Thousands, shares in Millions	3 Months Ended
Mar. 31, 2018	Feb. 11, 2014
Debt Instrument [Line Items]
Remaining principal amount	$ 21,417
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	$ 21,400

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

No definition available.

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Period Type:	instant

- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-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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Period Type:	instant

- 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 the hedged item as of the balance sheet date related to the derivative. For example, the hedged balance on a debt instrument.

+ References

No definition available.

+ Details

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- Definition

Amount of long-term debt payable, sinking fund requirements, and other securities issued that are redeemable by holder at fixed or determinable prices and dates maturing in the second fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 10
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6802200&loc=d3e1835-112601

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 3
-Subparagraph (SX 210.12-04.(a))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e24072-122690

+ Details

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Balance Type:	credit
Period Type:	instant

- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 40
-Section 50
-Paragraph 5
-Subparagraph (a)(3)
-URI http://asc.fasb.org/extlink&oid=6445032&loc=d3e90205-114008

+ 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://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 480
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (f)(1)
-URI http://asc.fasb.org/extlink&oid=6940734&loc=d3e22047-110879

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

+ Details

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Balance Type:	na
Period Type:	duration

- Definition

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

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
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Period Type:	instant

- Details

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- Details

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- Details

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- Details

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