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		6 Months Ended
	Jul. 31, 2012	Jul. 31, 2011	Jul. 31, 2012	Jul. 31, 2011
Debt Instrument [Line Items]
Interest expense at the contractual interest rate	$ 4,737	$ 4,634	$ 9,331	$ 22,074
6.25% Debentures due 2026, issued 2006
Debt Instrument [Line Items]
Interest expense at the contractual interest rate	0	0	0	2,900
Amortization of debt discount	$ 0	$ 0	$ 0	$ 793