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	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			1.56%	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%
Expected volatility			63.97%	67.76%	66.51%	67.28%	67.98%	68.34%	70.25%
Term			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	$ 0.2	$ 0.2	$ 0.2	$ 0.3	$ 0.2
November 2014 Warrant
Derivative [Line Items]
Risk-free interest rate			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%
Expected volatility			65.64%	67.21%	66.53%	69.31%	68.96%	70.01%	69.88%
Term			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			$ 0.8	$ 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