Net Income Per Share Data - Additional Information (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Nov. 05, 2014
Earnings Loss Per Share [Line Items]
Weighted average diluted shares outstanding excluded outstanding stock options	100,000	300,000	100,000	200,000
Common stock repurchased, shares	169,868
Stock repurchased average price per share	$ 23.78
Common stock repurchased	$ 4,000,000
Amount available for future repurchases under the current authorization	$ 26,000,000		$ 26,000,000
Accelerated Share Repurchase Program [Member]
Earnings Loss Per Share [Line Items]
Maximum payments for repurchase of common stock					$ 30,000,000