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

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Remaining amortization period for discount on the liability component of convertible debt which may be settled in cash upon conversion, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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

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

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

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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.

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Amount, after accumulated amortization, of debt discount (premium).

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Fair value as of the balance sheet date of the embedded derivative or group of embedded derivatives classified as a liability.

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Net Increase or Decrease in the fair value of the embedded derivative or group of embedded derivatives included in earnings in the period.

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Derivative Financial Instruments - 6% Convertible Promissory Notes (Additional Information) (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017	Jul. 01, 2017	Sep. 20, 2016	Sep. 10, 2016	Jan. 29, 2016	Dec. 15, 2015
Debt Instrument [Line Items]
Interest rate percentage					8.00%
6% Convertible Promissory Notes \| Convertible promissory notes
Debt Instrument [Line Items]
Interest rate percentage	6.00%	5.00%	6.00%	5.00%		6.00%
Debt face amount							$ 75,000,000	$ 75,000,000	$ 25,000,000	$ 160,000,000
Convertible stock price (in dollars per share)	$ 46.37		$ 46.37							$ 46.37
Convertible debt, stock price trigger			75.00%
Discount on convertible debt								6,300,000
Embedded derivative liability								$ 115,800,000
Accelerated amortization period			3 years
Gain (loss) on embedded derivative	$ (23,500,000)	$ (500,000)	$ 2,400,000	$ (31,000,000)