Term Receivable and Trade Accounts Receivable Balances (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Jan. 31, 2014	Jan. 31, 2013	Jan. 31, 2012	Jan. 31, 2011
Term Receivable and Trade Accounts Receivable
Trade and term receivables	$ 454,483	$ 412,245
Term receivables, long-term	270,365	250,497
Billing period	30 days
Allowance for doubtful accounts receivable, current	5,469	5,331	4,432	3,941
Provision for doubtful accounts	517	1,147	688
Net other deductions recoveries	(379)	(248)	(197)
Trade accounts receivable
Term Receivable and Trade Accounts Receivable
Trade and term receivables	179,830	178,351
Term Receivabes Current
Term Receivable and Trade Accounts Receivable
Trade and term receivables	274,653	233,894
External Credit Rating, Investment Grade
Term Receivable and Trade Accounts Receivable
Term receivables, long-term	180,113	133,773
External Credit Rating, Non Investment Grade
Term Receivable and Trade Accounts Receivable
Term receivables, long-term	29,654	45,298
External Credit Rating, Standard & Poor's
Term Receivable and Trade Accounts Receivable
Term receivables, long-term	209,767	179,071
Internal Credit Rating
Term Receivable and Trade Accounts Receivable
Term receivables, long-term	$ 60,598	$ 71,426