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Fair Value-Based Measurements and Weighted-Average Assumptions (Detail) (USD $) | 12 Months Ended
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Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012
Employee Stock Purchase Plan |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |
Weighted-average fair value | $ 7.45 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue / us-gaap_SubsidiarySaleOfStockAxis = us-gaap_EmployeeStockMember | $ 9.30 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue / us-gaap_SubsidiarySaleOfStockAxis = us-gaap_EmployeeStockMember | $ 35.40 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue / us-gaap_SubsidiarySaleOfStockAxis = us-gaap_EmployeeStockMember
Risk-free interest rate | 0.20%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate / us-gaap_SubsidiarySaleOfStockAxis = us-gaap_EmployeeStockMember | 0.20%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate / us-gaap_SubsidiarySaleOfStockAxis = us-gaap_EmployeeStockMember | 0.20%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate / us-gaap_SubsidiarySaleOfStockAxis = us-gaap_EmployeeStockMember
Expected life (in years) | 1 year 2 months 12 days | 1 year 3 months 18 days | 1 year 1 month 6 days
Volatility | 0.90%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate / us-gaap_SubsidiarySaleOfStockAxis = us-gaap_EmployeeStockMember | 0.80%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate / us-gaap_SubsidiarySaleOfStockAxis = us-gaap_EmployeeStockMember | 1.60%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate / us-gaap_SubsidiarySaleOfStockAxis = us-gaap_EmployeeStockMember
Stock Options |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |
Weighted-average fair value | $ 15.16 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue / us-gaap_AwardTypeAxis = us-gaap_EmployeeStockOptionMember | $ 24.15 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue / us-gaap_AwardTypeAxis = us-gaap_EmployeeStockOptionMember | $ 33.00 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue / us-gaap_AwardTypeAxis = us-gaap_EmployeeStockOptionMember
Risk-free interest rate | 1.80%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate / us-gaap_AwardTypeAxis = us-gaap_EmployeeStockOptionMember | 1.10%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate / us-gaap_AwardTypeAxis = us-gaap_EmployeeStockOptionMember | 0.50%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate / us-gaap_AwardTypeAxis = us-gaap_EmployeeStockOptionMember
Expected life (in years) | 5 years 10 months 24 days | 5 years 10 months 24 days | 4 years 2 months 12 days
Volatility | 1.40%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate / us-gaap_AwardTypeAxis = us-gaap_EmployeeStockOptionMember | 1.40%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate / us-gaap_AwardTypeAxis = us-gaap_EmployeeStockOptionMember | 1.60%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate / us-gaap_AwardTypeAxis = us-gaap_EmployeeStockOptionMember

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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. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SAB TOPIC 14.D.2) -URI http://asc.fasb.org/extlink&oid=27013229&loc=d3e301413-122809 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (f)(2)(i) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Staff Accounting Bulletin (SAB) -Number Topic 14 -Section D -Subsection 2 + Details
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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. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (f)(2)(ii) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition The risk-free interest rate assumption that is used in valuing an option on its own shares. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (f)(2)(iv) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (d)(1) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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