Notes Payable - Recognized Amounts in Interest Expense in the Condensed Consolidated Statement of Operations Related to the 4.00% Debentures (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Jan. 31, 2014	Jan. 31, 2013	Jan. 31, 2012
Debt Instrument
Interest expense at the contractual interest rate	$ 19,452	$ 18,866	$ 31,444
4.00% Debentures due 2031
Debt Instrument
Interest expense at the contractual interest rate	10,120	10,120	8,349
Amortization of debt discount	$ 5,715	$ 5,322	$ 4,154

Amount of noncash expense included in interest expense to amortize debt discount and premium associated with the related debt instruments. Excludes amortization of financing costs. Alternate captions include noncash interest expense.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 835

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-Section 45

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Reference 2: http://www.xbrl.org/2003/role/presentationRef

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-Name Accounting Standards Codification

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Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

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