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Short-Term Borrowings - Additional Information (Detail) (USD $)
In Thousands, unless otherwise specified
3 Months Ended
Apr. 30, 2015
Apr. 30, 2014
Line of Credit Facility [Line Items]    
Amount outstanding $ 0us-gaap_LineOfCredit $ 0us-gaap_LineOfCredit
Revolving credit facility    
Line of Credit Facility [Line Items]    
Termination date for senior, unsecured revolving credit facility Jan. 09, 2020  
Revolving credit facility, maximum borrowing capacity 125,000us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
/ us-gaap_CreditFacilityAxis
= us-gaap_RevolvingCreditFacilityMember
 
Credit facility limits, aggregate amount available for dividend and repurchase of stock $ 50,000ment_MaximumAmountAvailableForDividendsAndStockRepurchaseDollarLimit
/ us-gaap_CreditFacilityAxis
= us-gaap_RevolvingCreditFacilityMember
 
Credit facility limits, aggregate amount available for dividend and repurchase of stock, percentage of cumulative net income 70.00%ment_AmountAvailableForDividendDistributionPercentOfCumulativeNetIncome
/ us-gaap_CreditFacilityAxis
= us-gaap_RevolvingCreditFacilityMember
 
Minimum | Revolving credit facility    
Line of Credit Facility [Line Items]    
Commitment fee percentage on unused line of credit 0.30%us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage
/ us-gaap_CreditFacilityAxis
= us-gaap_RevolvingCreditFacilityMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
 
Minimum | LIBOR | Revolving credit facility    
Line of Credit Facility [Line Items]    
Basis spread 2.00%us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
/ us-gaap_CreditFacilityAxis
= us-gaap_RevolvingCreditFacilityMember
/ us-gaap_DebtInstrumentAxis
= ment_LIBORMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
 
Minimum | Base rate | Revolving credit facility    
Line of Credit Facility [Line Items]    
Basis spread 1.00%us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
/ us-gaap_CreditFacilityAxis
= us-gaap_RevolvingCreditFacilityMember
/ us-gaap_DebtInstrumentAxis
= us-gaap_BaseRateMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
 
Maximum | Revolving credit facility    
Line of Credit Facility [Line Items]    
Commitment fee percentage on unused line of credit 0.40%us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage
/ us-gaap_CreditFacilityAxis
= us-gaap_RevolvingCreditFacilityMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
 
Maximum | LIBOR | Revolving credit facility    
Line of Credit Facility [Line Items]    
Basis spread 2.50%us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
/ us-gaap_CreditFacilityAxis
= us-gaap_RevolvingCreditFacilityMember
/ us-gaap_DebtInstrumentAxis
= ment_LIBORMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
 
Maximum | Base rate | Revolving credit facility    
Line of Credit Facility [Line Items]    
Basis spread 1.50%us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
/ us-gaap_CreditFacilityAxis
= us-gaap_RevolvingCreditFacilityMember
/ us-gaap_DebtInstrumentAxis
= us-gaap_BaseRateMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember