Credit Risk Assessment for Long-term Receivables (Detail) (USD $) In Thousands, unless otherwise specified	Apr. 30, 2013	Jan. 31, 2013
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term receivables, long-term	$ 228,425	$ 250,497
S&P credit rating, AAA+ through BBB-
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term receivables, long-term	131,007	133,773
S&P credit rating, BB+ and lower
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term receivables, long-term	35,275	45,298
S&P credit rating
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term receivables, long-term	166,282	179,071
Internal Credit Rating [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term receivables, long-term	$ 62,143	$ 71,426