Quarterly report pursuant to Section 13 or 15(d)

Stock Based Compensation - Weighted-Average Fair Value Valuation Assumptions (Detail)

v3.5.0.2
Stock Based Compensation - Weighted-Average Fair Value Valuation Assumptions (Detail) - $ / shares
3 Months Ended 9 Months Ended
Sep. 30, 2016
Sep. 30, 2015
Sep. 30, 2016
Sep. 30, 2015
Employee Stock Options        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Risk-free interest rate 1.60% 1.77% 1.60% 1.70%
Expected term (in years) 5 years 11 months 19 days 6 years 29 days 5 years 11 months 19 days 5 years 11 months 27 days
Dividend yield 0.00% 0.00% 0.00% 0.00%
Volatility 108.00% 79.00% 108.00% 82.00%
Weighted-average fair value of stock options granted $ 0.44 $ 2.98 $ 0.44 $ 3.08
Employee Stock Purchase Plan (ESPP)        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Risk-free interest rate 0.56% 0.45% 0.56% 0.39%
Expected term (in years) 1 year 2 months 27 days 1 year 3 months 1 year 2 months 27 days 1 year 2 months 27 days
Dividend yield 0.00% 0.00% 0.00% 0.00%
Volatility 161.00% 50.00% 161.00% 50.00%
Weighted-average fair value of ESPP purchase rights $ 0.22 $ 1.55 $ 0.22 $ 1.58