Equity Incentive Plans - Fair Value of Each Stock Option Granted Weighted-Average Assumptions (Detail) - $ / shares |
12 Months Ended | |
|---|---|---|
Dec. 31, 2015 |
Dec. 31, 2014 |
|
| Disclosure Of Compensation Related Costs Sharebased Payments [Abstract] | ||
| Fair value of options granted | $ 4.10 | $ 3.26 |
| Expected volatility | 84.00% | 117.00% |
| Risk-free interest rate | 1.60% | 2.00% |
| Expected lives | 6 years | 6 years 1 month 6 days |
| Dividend rate | 1.60% | 2.30% |