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Summary of Other Information Related to Stock Options (Detail) (USD $)
In Thousands, except Per Share data, unless otherwise specified
12 Months Ended
Jan. 31, 2015
Jan. 31, 2014
Jan. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Net cash proceeds from the exercise of stock options $ 10,693us-gaap_ProceedsFromStockOptionsExercised $ 35,218us-gaap_ProceedsFromStockOptionsExercised $ 30,671us-gaap_ProceedsFromStockOptionsExercised
Stock Options      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Weighted-average grant date fair value-per share $ 7.02us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
$ 9.67us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
$ 7.71us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
Intrinsic value of awards exercised 4,852us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
30,450us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
19,544us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
Net cash proceeds from the exercise of stock options $ 10,693us-gaap_ProceedsFromStockOptionsExercised
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
$ 35,218us-gaap_ProceedsFromStockOptionsExercised
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
$ 30,671us-gaap_ProceedsFromStockOptionsExercised
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember