Credit Risk Assessment for Long-term Receivables (Detail) (USD $) In Thousands, unless otherwise specified	Jan. 31, 2012	Jan. 31, 2011
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term receivables, long-term	$ 220,355	$ 167,425
S&P credit rating, AAA+ through BBB-
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term receivables, long-term	130,545	84,685
S&P credit rating, BB+ and lower
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term receivables, long-term	15,161	19,473
S&P credit rating
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term receivables, long-term	145,706	104,158
Internal credit assessment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term receivables, long-term	$ 74,649	$ 63,267