Credit Risk Assessment for Long-term Receivables (Details) (USD $) In Thousands, unless otherwise specified	Jan. 31, 2015	Jan. 31, 2014
Accounts and Financing Receivable [Line Items]
Term receivables, long-term	$ 301,862	$ 270,365
S&P credit rating, AAA+ through BBB-
Accounts and Financing Receivable [Line Items]
Term receivables, long-term	192,430	180,113
S&P credit rating, BB+ and lower
Accounts and Financing Receivable [Line Items]
Term receivables, long-term	31,939	29,654
S&P credit rating
Accounts and Financing Receivable [Line Items]
Term receivables, long-term	224,369	209,767
Internal Credit Rating
Accounts and Financing Receivable [Line Items]
Term receivables, long-term	$ 77,493	$ 60,598