General Information and Accounting Policies (Details 2) (USD $) In Millions, unless otherwise specified	3 Months Ended
Aug. 31, 2013	Aug. 31, 2012
Loan Sales
Obligation to repurchase loans from the purchaser, except in the case of breaches of representations and warranties	$ 0
Carrying amount of loans sold	$ 11	$ 14

Represents the amount of obligations to repurchase the loans sold from the purchaser except in case of breaches of representations and warranties.

No definition available.

Name:	nrc_ObligationToRepurchaseLoansExceptInCaseOfBreachesOfRepresentationsAndWarranties
Namespace Prefix:	nrc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant