Notes Payable - Recognized Amounts in Interest Expense in the Condensed Consolidated Statement of Operations Related to the 6.25% Debentures (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Apr. 30, 2012	Apr. 30, 2011
Debt Instrument [Line Items]
Interest expense at the contractual interest rate	$ 4,594	$ 17,440
6.25% Debentures due 2026, issued 2006
Debt Instrument [Line Items]
Interest expense at the contractual interest rate	0	2,900
Amortization of debt discount	$ 0	$ 793