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Notes Payable - Principal Amount, Unamortized Debt Discount, Net Carrying Amount of the Liability Component, and Carrying Amount of the Equity Component of the 4.00% Debentures (Details) (4.00% Debentures due 2031, USD $)
In Thousands, unless otherwise specified
Jan. 31, 2015
Jan. 31, 2014
4.00% Debentures due 2031
    
Debt Instrument    
Principal amount $ 253,000us-gaap_DebtInstrumentCarryingAmount
/ us-gaap_DebtInstrumentAxis
= ment_Debentures4PercentDue2031Member		 $ 253,000us-gaap_DebtInstrumentCarryingAmount
/ us-gaap_DebtInstrumentAxis
= ment_Debentures4PercentDue2031Member
Unamortized debt discount (22,600)us-gaap_DebtInstrumentUnamortizedDiscount
/ us-gaap_DebtInstrumentAxis
= ment_Debentures4PercentDue2031Member		 (28,739)us-gaap_DebtInstrumentUnamortizedDiscount
/ us-gaap_DebtInstrumentAxis
= ment_Debentures4PercentDue2031Member
Net carrying amount of the liability component 230,400us-gaap_NotesPayable
/ us-gaap_DebtInstrumentAxis
= ment_Debentures4PercentDue2031Member		 224,261us-gaap_NotesPayable
/ us-gaap_DebtInstrumentAxis
= ment_Debentures4PercentDue2031Member
Equity component $ 43,930us-gaap_DebtInstrumentConvertibleCarryingAmountOfTheEquityComponent
/ us-gaap_DebtInstrumentAxis
= ment_Debentures4PercentDue2031Member		 $ 43,930us-gaap_DebtInstrumentConvertibleCarryingAmountOfTheEquityComponent
/ us-gaap_DebtInstrumentAxis
= ment_Debentures4PercentDue2031Member