Credit Risk Assessment for Long-term Receivables (Detail) (USD $) In Thousands, unless otherwise specified	Jul. 31, 2012	Jan. 31, 2012
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term receivables, long-term	$ 217,338	$ 220,355
S&P credit rating, AAA+ through BBB-
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term receivables, long-term	130,519	130,545
S&P credit rating, BB+ and lower
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term receivables, long-term	28,164	15,161
S&P credit rating
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term receivables, long-term	158,683	145,706
Internal Credit Rating [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term receivables, long-term	$ 58,655	$ 74,649