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Income Taxes - Reconciliation of Statutory Federal Income Tax to Effective Tax (Detail) (USD $)
In Thousands, unless otherwise specified
3 Months Ended 12 Months Ended
Jan. 31, 2015
Oct. 31, 2014
Jul. 31, 2014
Apr. 30, 2014
Jan. 31, 2014
Oct. 31, 2013
Jul. 31, 2013
Apr. 30, 2013
Jan. 31, 2015
Jan. 31, 2014
Jan. 31, 2013
Income Tax Disclosure [Abstract]                      
Federal tax statutory tax rate                 $ 23,470us-gaap_IncomeTaxReconciliationIncomeTaxExpenseBenefitAtFederalStatutoryIncomeTaxRate $ 13,475us-gaap_IncomeTaxReconciliationIncomeTaxExpenseBenefitAtFederalStatutoryIncomeTaxRate $ 10,182us-gaap_IncomeTaxReconciliationIncomeTaxExpenseBenefitAtFederalStatutoryIncomeTaxRate
State taxes                 1,429us-gaap_IncomeTaxReconciliationStateAndLocalIncomeTaxes 904us-gaap_IncomeTaxReconciliationStateAndLocalIncomeTaxes 880us-gaap_IncomeTaxReconciliationStateAndLocalIncomeTaxes
Nondeductible expenses                 140us-gaap_IncomeTaxReconciliationNondeductibleExpense 55us-gaap_IncomeTaxReconciliationNondeductibleExpense 80us-gaap_IncomeTaxReconciliationNondeductibleExpense
Research and development credit                 (2,028)us-gaap_IncomeTaxReconciliationTaxCreditsResearch (880)us-gaap_IncomeTaxReconciliationTaxCreditsResearch (351)us-gaap_IncomeTaxReconciliationTaxCreditsResearch
Domestic manufacturing deduction                 (431)us-gaap_IncomeTaxReconciliationDeductions (1,124)us-gaap_IncomeTaxReconciliationDeductions (699)us-gaap_IncomeTaxReconciliationDeductions
Stock-based compensation                 2,506us-gaap_IncomeTaxReconciliationNondeductibleExpenseShareBasedCompensationCost 1,802us-gaap_IncomeTaxReconciliationNondeductibleExpenseShareBasedCompensationCost 231us-gaap_IncomeTaxReconciliationNondeductibleExpenseShareBasedCompensationCost
Foreign rate differential                 1,101us-gaap_IncomeTaxReconciliationForeignIncomeTaxRateDifferential (164)us-gaap_IncomeTaxReconciliationForeignIncomeTaxRateDifferential (50)us-gaap_IncomeTaxReconciliationForeignIncomeTaxRateDifferential
Valuation allowance                 1,589us-gaap_IncomeTaxReconciliationChangeInDeferredTaxAssetsValuationAllowance 512us-gaap_IncomeTaxReconciliationChangeInDeferredTaxAssetsValuationAllowance (52)us-gaap_IncomeTaxReconciliationChangeInDeferredTaxAssetsValuationAllowance
Others                 (973)us-gaap_IncomeTaxReconciliationOtherReconcilingItems 305us-gaap_IncomeTaxReconciliationOtherReconcilingItems 89us-gaap_IncomeTaxReconciliationOtherReconcilingItems
Provision for income taxes $ 5,697us-gaap_IncomeTaxExpenseBenefit $ 8,694us-gaap_IncomeTaxExpenseBenefit $ 7,106us-gaap_IncomeTaxExpenseBenefit $ 5,306us-gaap_IncomeTaxExpenseBenefit $ 4,696us-gaap_IncomeTaxExpenseBenefit $ 3,585us-gaap_IncomeTaxExpenseBenefit $ 3,775us-gaap_IncomeTaxExpenseBenefit $ 2,829us-gaap_IncomeTaxExpenseBenefit $ 26,803us-gaap_IncomeTaxExpenseBenefit $ 14,885us-gaap_IncomeTaxExpenseBenefit $ 10,310us-gaap_IncomeTaxExpenseBenefit