Term Receivable and Trade Accounts Receivable Balances (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Jan. 31, 2013	Jan. 31, 2012	Jan. 31, 2011	Jan. 31, 2010
Accounts, Notes, Loans and Financing Receivable [Line Items]
Trade and term receivables	$ 412,245	$ 354,924
Term receivables, long-term	250,497	220,355
Billing Period	30 days
Allowance for Doubtful Accounts Receivable, Current	5,331	4,432	3,941	3,607
Provision for Doubtful Accounts	1,147	688	369
Net Deductions Recoveries	(248)	(197)	(35)
Proceeds from Sale of Finance Receivables	20,198	29,146	51,601
External Credit Rating, Investment Grade [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term receivables, long-term	133,773	130,545
External Credit Rating, Non Investment Grade [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term receivables, long-term	45,298	15,161
External Credit Rating, Standard & Poor's [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term receivables, long-term	179,071	145,706
Internal Credit Rating [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term receivables, long-term	71,426	74,649
Trade accounts receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Trade and term receivables	178,351	133,494
Term Receivabes Current [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Trade and term receivables	$ 233,894	$ 221,430