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Stock Option and Purchase Plans - Fair Value for Options Granted under Employee Stock Purchase Plan (Detail)
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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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| Employee Stock Ownership Plan (ESOP) Disclosures [Line Items] | |||
| Dividend Yield | 0.00%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate | 0.00%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate | 0.00%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate |
| Employee Stock [Member] | |||
| Employee Stock Ownership Plan (ESOP) Disclosures [Line Items] | |||
| Risk-free Interest Rate |
0.10%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate / us-gaap_SubsidiarySaleOfStockAxis = us-gaap_EmployeeStockMember |
0.10%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate / us-gaap_SubsidiarySaleOfStockAxis = us-gaap_EmployeeStockMember |
0.17%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate / us-gaap_SubsidiarySaleOfStockAxis = us-gaap_EmployeeStockMember |
| Dividend Yield |
0.00%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate / us-gaap_SubsidiarySaleOfStockAxis = us-gaap_EmployeeStockMember |
0.00%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate / us-gaap_SubsidiarySaleOfStockAxis = us-gaap_EmployeeStockMember |
0.00%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate / us-gaap_SubsidiarySaleOfStockAxis = us-gaap_EmployeeStockMember |
| Volatility Factor |
0.42%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate / us-gaap_SubsidiarySaleOfStockAxis = us-gaap_EmployeeStockMember |
0.37%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate / us-gaap_SubsidiarySaleOfStockAxis = us-gaap_EmployeeStockMember |
0.37%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate / us-gaap_SubsidiarySaleOfStockAxis = us-gaap_EmployeeStockMember |
| Expected Life in Years | 1 year | 1 year | 1 year |
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- Details
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- Definition
The estimated dividend rate (a percentage of the share price) to be paid (expected dividends) to holders of the underlying shares over the option's term. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition
Expected term of share-based compensation awards, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition
The estimated measure of the percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition
The risk-free interest rate assumption that is used in valuing an option on its own shares. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Details
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