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Warrants and Derivative Liabilities - Schedule of Assumptions Used to Calculate the Fair Value of Warrants (Detail) - USD ($) $ in Millions |  | 3 Months Ended
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Dec. 19, 2014 | Mar. 31, 2017 | Dec. 31, 2016 | Sep. 30, 2016 | Jun. 30, 2016 | Mar. 31, 2016 | Dec. 31, 2015 | Sep. 30, 2015 | Jun. 30, 2015 | Mar. 31, 2015 | Dec. 31, 2014 | Sep. 30, 2014 | Jun. 30, 2014 | Mar. 31, 2014
Exchanged warrants |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Risk-free interest rate |  | 0.91% | 0.56% | 0.59% | 0.48% | 0.66% | 0.96% | 0.64% | 0.74% | 0.73% | 1.00% | 1.07% | 0.98% | 1.11%
Expected annual dividend yield |  | 0.00% | 0.00% | 0.00% | 0.00% | 0.00% | 0.00% | 0.00% | 0.00% | 0.00% | 0.00% | 0.00% | 0.00% | 0.00%
Expected volatility |  | 44.12% | 58.04% | 70.50% | 76.30% | 76.76% | 76.68% | 73.39% | 71.61% | 70.42% | 72.38% | 76.20% | 83.50% | 80.99%
Term (years) |  | 6 months 4 days | 9 months 4 days | 1 year 4 days | 1 year 3 months 4 days | 1 year 6 months 4 days | 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 |  | $ 0.0 | $ 0.1 | $ 0.2 | $ 0.4 | $ 0.4 | $ 0.3 | $ 0.1 | $ 0.2 | $ 0.3 | $ 0.5 | $ 1.5 | $ 2.3 | $ 2.2
Hercules warrants |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Risk-free interest rate | 1.74% | 1.55% | 1.57% | 0.97% | 0.86% | 1.08% | 1.65% | 1.31% | 1.63% | 1.41% | 1.73% |  |  |
Expected annual dividend yield | 0.00% | 0.00% | 0.00% | 0.00% | 0.00% | 0.00% | 0.00% | 0.00% | 0.00% | 0.00% | 0.00% |  |  |
Expected volatility | 70.26% | 66.51% | 67.28% | 67.98% | 68.34% | 70.25% | 73.57% | 75.32% | 72.57% | 74.60% | 77.43% |  |  |
Term (years) | 5 years 6 months 11 days | 3 years 3 months | 3 years 6 months | 3 years 9 months | 4 years | 4 years 3 months | 4 years 6 months | 4 years 9 months | 5 years | 5 years 3 months | 5 years 6 months |  |  |
Fair value | $ 0.2 | $ 0.2 | $ 0.2 | $ 0.2 | $ 0.3 | $ 0.2 | $ 0.2 | $ 0.1 | $ 0.2 | $ 0.2 | $ 0.2 |  |  |
November 2014 warrant |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Risk-free interest rate | 1.64% | 1.41% | 1.43% | 0.93% | 0.77% | 0.98% | 1.51% | 1.17% | 1.44% | 1.28% | 1.61% |  |  |
Expected annual dividend yield | 0.00% | 0.00% | 0.00% | 0.00% | 0.00% | 0.00% | 0.00% | 0.00% | 0.00% | 0.00% | 0.00% |  |  |
Expected volatility | 72.86% | 66.53% | 69.31% | 68.96% | 70.01% | 69.88% | 70.02% | 73.02% | 74.18% | 75.96% | 78.00% |  |  |
Term (years) | 5 years | 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 | 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 | $ 1.8 | $ 2.3 | $ 2.3 | $ 3.2 | $ 2.6 | $ 2.1 | $ 1.3 | $ 1.8 | $ 2.5 | $ 3.2 |  |  |

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