Convertible Notes - Estimated Fair Values (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	12 Months Ended
Mar. 31, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Dividend yield	0.00%
Compounded Bifurcated Derivatives \| Binomial Lattice Model
Debt Instrument [Line Items]
Calculated aggregate value	$ 3,193	$ 3,136
Closing price per share of common stock (usd per share)	$ 0.59	$ 0.64
Contractual remaining term	8 years 5 months	8 years 8 months
Contractual interest rate	4.00%	4.00%
Volume-weighted average conversion rate (usd per share)	$ 3.40933	$ 3.40933
Dividend yield	0.00%	0.00%
Credit Spread	35.50%	36.98%
Volatility	98.10%	99.00%
Compounded Bifurcated Derivatives \| Binomial Lattice Model \| Minimum
Debt Instrument [Line Items]
Risk-free interest rate (term structure)	1.63%	1.28%
Compounded Bifurcated Derivatives \| Binomial Lattice Model \| Maximum
Debt Instrument [Line Items]
Risk-free interest rate (term structure)	2.74%	2.40%

Closing price per share of common stock.

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- Definition

Fair Value Assumptions, Volume-weighted Average Conversion Rate

+ References

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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

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- Definition

Fixed interest rate related to the interest rate derivative.

+ References

No definition available.

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- Definition

Fair value, after the effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities not subject to a master netting arrangement and not elected to be offset.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=82849420&loc=SL20226008-175313

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-Topic 825
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-Section 50
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- Definition

Expected dividends to be paid to holders of the underlying shares or financial instruments (expressed as a percentage of the share or instrument's price).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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- Definition

Period the instrument, asset or liability is expected to be outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

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- Definition

Measure of dispersion, in percentage terms (for instance, the standard deviation or variance), for a given stock price.

+ References

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- Definition

Risk-free interest rate assumption used in valuing an instrument.

+ References

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- Definition

Risk associated with risk of default, credit spread risk and downgrade risk, expressed as a percentage, used as an input to measure fair value.

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