Debt - 2016 Convertible Notes (Details Textual) - Senior Convertible Notes 2016 $ / shares in Units, $ in Thousands	3 Months Ended	12 Months Ended
Mar. 31, 2018 USD ($) Tradingday $ / shares	Dec. 31, 2017 USD ($) $ / shares
Debt Instrument [Line Items]
Percentage of par value of convertible notes to be settled in cash	100.00%
Conversion rate of common stock	17.4951	17.4858
Convertible Notes, initial conversion of Par Value Convertible Notes to common stock \| $	$ 1	$ 1
Conversion price \| $ / shares	$ 57.16	$ 57.19
Rate of conversion price	130.00%
Debt instrument, convertible, threshold consecutive trading days	30
Debt instrument, convertible, threshold trading days	20

The percentage amount of the par value of debt that will be settled in cash.

No definition available.

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- Definition

The amount of the original debt being converted in a noncash (or part noncash) transaction. "Part noncash" refers to that portion of the transaction not resulting in cash receipts or cash payments in the period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=98513485&loc=d3e4304-108586

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=98513485&loc=d3e4332-108586

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- Definition

The price per share of the conversion feature embedded in the debt instrument.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 5
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=6928298&loc=SL6031898-161870

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- Definition

Ratio applied to the conversion of debt instrument into equity with equity shares divided by debt principal amount.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 6
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=84159872&loc=d3e21506-112644

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-Name Accounting Standards Codification
-Topic 505
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-Section 50
-Paragraph 3
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-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
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-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(5))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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- Definition

Threshold period of specified consecutive trading days within which common stock price to conversion price of convertible debt instrument must exceed threshold percentage for specified number of trading days to trigger conversion feature.

+ References

No definition available.

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- Definition

Minimum percentage of common stock price to conversion price of convertible debt instruments to determine eligibility of conversion.

+ References

No definition available.

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- Definition

Threshold number of specified trading days that common stock price to conversion price of convertible debt instruments must exceed threshold percentage within a specified consecutive trading period to trigger conversion feature.

+ References

No definition available.

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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.

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