Annual report pursuant to Section 13 and 15(d)

Equity Incentive Plans and Stock Based Compensation - Weighted-Average Fair Value Valuation Assumptions (Detail)

v3.7.0.1
Equity Incentive Plans and Stock Based Compensation - Weighted-Average Fair Value Valuation Assumptions (Detail) - $ / shares
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Employee Stock Options      
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Risk-free interest rate 1.60% 1.70% 1.83%
Expected life (in years) 5 years 11 months 19 days 5 years 11 months 27 days 5 years 11 months 23 days
Dividend yield 0.00% 0.00% 0.00%
Volatility 108.00% 83.00% 94.00%
Weighted-average fair value of stock options granted $ 0.44 $ 3.06 $ 2.89
Employee Stock Purchase Plan (ESPP)      
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Risk-free interest rate 0.56% 0.39% 0.20%
Expected life (in years) 1 year 2 months 27 days 1 year 2 months 27 days 1 year 2 months 27 days
Dividend yield 0.00% 0.00% 0.00%
Volatility 161.00% 50.00% 49.00%
Weighted-average fair value of ESPP purchase rights $ 0.22 $ 1.58 $ 1.60