401(k) Plan (Narrative) (Detail) - USD ($)	3 Months Ended		6 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2016	Dec. 31, 2015
Napco Technologies 401 k Plan [Member]
Schedule of Deferred Compensation Plans [Line Items]
Deferred compensation plan expense	$ 27,000	$ 27,000	$ 55,000	$ 55,000