Warrants and Derivative Liabilities - Schedule of Assumptions Used to Calculate the Fair Value of Exchanged Warrants (Detail) - USD ($) $ in Millions	3 Months Ended
Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016
Exchanged Warrants
Derivative [Line Items]
Risk-free interest rate	1.05%	0.91%	0.56%	0.59%	0.48%	0.66%
Expected annual dividend yield	0.00%	0.00%	0.00%	0.00%	0.00%	0.00%
Expected volatility	78.25%	44.12%	58.04%	70.50%	76.30%	76.76%
Term	3 months 4 days	6 months 4 days	9 months 4 days	1 year 4 days	1 year 3 months 4 days	1 year 6 months 4 days
Fair value	$ 0.0	$ 0.0	$ 0.1	$ 0.2	$ 0.4	$ 0.4
Hercules Warrants
Derivative [Line Items]
Risk-free interest rate	1.58%	1.55%	1.57%	0.97%	0.86%	1.08%
Expected annual dividend yield	0.00%	0.00%	0.00%	0.00%	0.00%	0.00%
Expected volatility	67.76%	66.51%	67.28%	67.98%	68.34%	70.25%
Term	2 years 11 months 20 days	3 years 3 months	3 years 6 months	3 years 9 months	4 years	4 years 3 months
Fair value	$ 0.1	$ 0.2	$ 0.2	$ 0.2	$ 0.3	$ 0.2
November 2014 Warrant
Derivative [Line Items]
Risk-free interest rate	1.44%	1.41%	1.43%	0.93%	0.77%	0.98%
Expected annual dividend yield	0.00%	0.00%	0.00%	0.00%	0.00%	0.00%
Expected volatility	67.21%	66.53%	69.31%	68.96%	70.01%	69.88%
Term	2 years 4 months 13 days	2 years 7 months 13 days	2 years 10 months 13 days	3 years 1 month 13 days	3 years 4 months 13 days	3 years 7 months 13 days
Fair value	$ 0.9	$ 1.8	$ 2.3	$ 2.3	$ 3.2	$ 2.6

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

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
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (bbb)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258

+ Details

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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.

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