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	3 Months Ended
Apr. 30, 2014	Apr. 30, 2013
Debt Instrument
Interest expense at the contractual interest rate	$ 4,585	$ 4,785
4.00% Debentures due 2031
Debt Instrument
Interest expense at the contractual interest rate	2,530	2,530
Amortization of debt discount	$ 1,494	$ 1,391

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

-Publisher FASB

-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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-Publisher SEC

-Name Regulation S-X (SX)

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