Warrants and Derivative Liabilities - Schedule of Assumptions Used to Calculate the Fair Value of Exchanged Warrants (Detail) - USD ($) $ in Millions			3 Months Ended
Sep. 30, 2017	Sep. 25, 2017	Dec. 31, 2017	Sep. 30, 2017	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%	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%	0.00%
Expected volatility				77.95%	78.25%	44.12%	58.04%	70.50%	76.30%	76.76%
Term				4 days	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	$ 0.0	$ 0.1	$ 0.2	$ 0.4	$ 0.4
Hercules Warrants
Derivative [Line Items]
Risk-free interest rate			1.98%	1.56%	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%	0.00%	0.00%
Expected volatility			69.11%	63.97%	67.76%	66.51%	67.28%	67.98%	68.34%	70.25%
Term			2 years 5 months 15 days	2 years 8 months 20 days	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	$ 0.1	$ 0.1	$ 0.2	$ 0.2	$ 0.2	$ 0.3	$ 0.2
November 2014 Warrant
Derivative [Line Items]
Risk-free interest rate			1.87%	1.49%	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%	0.00%	0.00%
Expected volatility			65.86%	65.64%	67.21%	66.53%	69.31%	68.96%	70.01%	69.88%
Term			1 year 10 months 13 days	2 years 1 month 13 days	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			$ 0.4	$ 0.8	$ 0.9	$ 1.8	$ 2.3	$ 2.3	$ 3.2	$ 2.6
Acquisition contingent consideration
Derivative [Line Items]
Risk-free interest rate	1.09%	1.09%
Expected annual dividend yield	0.00%	0.00%
Expected volatility	66.54%	65.71%
Term	3 months 22 days	3 months 27 days
Fair value	$ 0.4	$ 0.6

Warrant instruments, fair value disclosure.

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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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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

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