Net Income Per Share Data - Additional Information (Detail) - USD ($)		3 Months Ended		6 Months Ended
	Nov. 11, 2014	Mar. 31, 2016	Mar. 31, 2015	Mar. 31, 2016	Mar. 31, 2015	Nov. 06, 2015	Nov. 05, 2014
Earnings Loss Per Share [Line Items]
Weighted average diluted shares outstanding excluded outstanding stock options		900,000	300,000	800,000	500,000
Common stock outstanding in additional						$ 10,000,000
Accelerated Share Repurchase Program [Member]
Earnings Loss Per Share [Line Items]
Maximum payments for repurchase of common stock						$ 20,000,000	$ 30,000,000
Fair value of common stock	$ 16,000,000
Initial payment to bank reported as reduction in retained earnings	$ 4,000,000
Common stock repurchased, Shares	847,864
Accelerate share repurchase program, price per share	$ 23.59
Accelerated Share Repurchase Program [Member] | Maximum [Member]
Earnings Loss Per Share [Line Items]
Reduction in common stock	$ 100,000
Reduction in additional paid-in capital	2,500,000
Reduction in retained earnings	13,500,000
Accelerated Share Repurchase Program [Member] | Investment Bank [Member]
Earnings Loss Per Share [Line Items]
Fair value of common stock	$ 20,000,000
Common stock repurchased, Shares	758,143