Defined Benefit Pension Plan - Additional information (Detail)	Sep. 30, 2012 Y
Defined Contribution Plan Disclosure [Line Items]
Years prior to retirement used to determine employee benefit under defined benefit pension plan	5

The period of service used in calculating an employee's benefit under a defined benefit pension plan.

No definition available.

Name:	naii_NumberOfYearsCompensationUsedForBenefitObligationAssumptions
Namespace Prefix:	naii_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant