Credit Risk Assessment for Long-term Receivables (Detail) (USD $) In Thousands, unless otherwise specified	Apr. 30, 2015	Jan. 31, 2015
Accounts and Financing Receivable [Line Items]
Term receivables, long-term	$ 282,343	$ 301,862
S&P credit rating, AAA+ through BBB-
Accounts and Financing Receivable [Line Items]
Term receivables, long-term	176,171	192,430
S&P credit rating, BB+ and lower
Accounts and Financing Receivable [Line Items]
Term receivables, long-term	41,658	31,939
S&P credit rating
Accounts and Financing Receivable [Line Items]
Term receivables, long-term	217,829	224,369
Internal Credit Rating
Accounts and Financing Receivable [Line Items]
Term receivables, long-term	$ 64,514	$ 77,493