Commitments - Additional Information (Detail) (Letter of Credit, USD $) In Millions, unless otherwise specified	6 Months Ended
Jul. 31, 2013
Letter of Credit
Debt Instrument [Line Items]
Value of outstanding letters of credit	$ 57.2
Letters of credit expiration dates	December 2030

The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

No definition available.

Name:	us-gaap_LettersOfCreditOutstandingAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant