Warrants and Derivative Liabilities - Schedule of Assumptions Used to Calculate the Fair Value of Exchanged Warrants (Detail) - USD ($) $ in Millions			3 Months Ended
Dec. 19, 2014	Nov. 13, 2014	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014
Senior Convertible Note Warrant
Derivative [Line Items]
Risk-free interest rate			0.96%	0.64%	0.74%	0.73%	1.00%	1.07%	0.98%	1.11%
Expected volatility			76.68%	73.39%	71.61%	70.42%	72.38%	76.20%	83.50%	80.99%
Term (years)			1 year 9 months 4 days	2 years 4 days	2 years 3 months 4 days	2 years 6 months 4 days	2 years 9 months 4 days	3 years 4 days	3 years 3 months 4 days	3 years 6 months 4 days
Fair value			$ 0.1	$ 0.1	$ 0.2	$ 0.3	$ 0.5	$ 1.5	$ 2.3	$ 2.2
Senior Secured Term Loan New Warrant
Derivative [Line Items]
Risk-free interest rate	1.74%		1.65%	1.31%	1.63%	1.41%	1.73%
Expected volatility	70.26%		73.57%	75.32%	72.57%	74.60%	77.43%
Term (years)	5 years 6 months 11 days		4 years 6 months	4 years 9 months	5 years	5 years 3 months	5 years 6 months
Fair value	$ 0.2		$ 3.1	$ 0.1	$ 0.2	$ 0.2	$ 0.2
November 2014 Warrant
Derivative [Line Items]
Risk-free interest rate		1.64%	1.51%	1.17%	1.44%	1.28%	1.61%
Expected volatility		72.86%	70.02%	73.02%	74.18%	75.96%	78.00%
Term (years)		5 years	3 years 10 months 13 days	4 years 1 month 13 days	4 years 4 months 13 days	4 years 7 months 13 days	4 years 10 months 13 days
Fair value		$ 4.3	$ 2.1	$ 1.3	$ 1.8	$ 2.5	$ 3.2

Warrant instruments, fair value disclosure.

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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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- 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

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (e)
-URI http://asc.fasb.org/extlink&oid=36462937&loc=d3e19207-110258

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

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- Definition

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

+ References

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