Credit Risk Assessment for Long-term Receivables (Detail) (USD $) In Thousands, unless otherwise specified	Apr. 30, 2012	Jan. 31, 2012
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term receivables, long-term	$ 212,665	$ 220,355
S&P credit rating, AAA+ through BBB-
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term receivables, long-term	134,324	130,545
S&P credit rating, BB+ and lower
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term receivables, long-term	18,211	15,161
S&P credit rating
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term receivables, long-term	152,535	145,706
Internal credit assessment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term receivables, long-term	$ 60,130	$ 74,649