Assumptions Used to Estimate Per Share Fair Value of Stock Options Granted (Detail) (Stock Option)
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12 Months Ended | ||
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Dec. 31, 2014
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Dec. 31, 2013
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Dec. 31, 2012
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Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | |||
Dividend yield | 0.00% | 0.00% | 0.00% |
Expected life | 6 years 10 months 24 days | 6 years 6 months | |
Minimum
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Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | |||
Expected volatility | 44.00% | 44.00% | 45.00% |
Expected life | 6 years 7 months 6 days | ||
Risk-free interest rate | 1.80% | 1.00% | 0.80% |
Maximum
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Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | |||
Expected volatility | 45.00% | 47.00% | 46.00% |
Expected life | 6 years 9 months 18 days | ||
Risk-free interest rate | 2.30% | 2.40% | 1.10% |