Assumptions to Estimate Fair Value for Stock Options at Grant Date (Detail) - Time Vested Stock Options |
3 Months Ended | 9 Months Ended | ||
---|---|---|---|---|
Sep. 30, 2015 |
Sep. 30, 2014 |
Sep. 30, 2015 |
Sep. 30, 2014 |
|
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | ||||
Expected life (in years) | 4 years | 4 years | ||
Risk-free interest rate | 1.45% | 1.26% | ||
Risk-free interest rate, minimum | 1.15% | 1.13% | ||
Risk-free interest rate, maximum | 1.56% | 1.56% | ||
Expected volatility | 62.00% | |||
Expected volatility, minimum | 59.00% | 59.00% | 55.00% | |
Expected volatility, maximum | 60.00% | 65.00% | 62.00% | |
Expected dividend yield | 0.00% | 0.76% | 0.76% | |
Minimum | ||||
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | ||||
Expected life (in years) | 4 years | 4 years | ||
Expected dividend yield | 0.00% | |||
Maximum | ||||
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | ||||
Expected life (in years) | 6 years 3 months | 6 years 3 months | ||
Expected dividend yield | 0.36% |