Stock-Based Compensation - Options Granted under Company's Stock Incentive Plans, Valuation Assumptions and Fair Values (Detail) - Stock Options [Member] - $ / shares |
3 Months Ended | 9 Months Ended | ||
---|---|---|---|---|
Sep. 30, 2018 |
Sep. 30, 2017 |
Sep. 30, 2018 |
Sep. 30, 2017 |
|
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | ||||
Average risk-free interest rate | 2.89% | 1.56% | 2.50% | 1.52% |
Expected dividend yield | 0.00% | 0.00% | 0.00% | 0.00% |
Expected life | 3 years 6 months | 3 years 6 months | 3 years 6 months | 3 years 6 months |
Expected volatility | 61.20% | |||
Weighted average exercise price | $ 2.91 | $ 4.28 | $ 3.08 | $ 4.39 |
Weighted average fair value | $ 1.34 | $ 2.02 | $ 1.41 | $ 2.12 |
Minimum [Member] | ||||
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | ||||
Expected volatility | 64.20% | 60.80% | 64.20% | |
Maximum [Member] | ||||
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | ||||
Expected volatility | 67.00% | 61.60% | 72.00% |