Credit Risk Assessment for Long-term Receivables (Detail) (USD $) In Thousands	Jul. 31, 2011	Jan. 31, 2011
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term receivables, long-term	$ 186,483	$ 167,425
S&P credit rating, AAA+ through BBB-
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term receivables, long-term	105,575	84,685
S&P credit rating, BB+ and lower
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term receivables, long-term	10,360	19,473
S&P credit rating
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term receivables, long-term	115,935	104,158
Internal credit assessment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term receivables, long-term	$ 70,548	$ 63,267