Stockholders' Equity - Additional Information (Detail) - USD ($)					12 Months Ended
	Jul. 08, 2015	Nov. 11, 2014	Sep. 30, 2013	Jun. 30, 2013	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2013	Nov. 06, 2015	Nov. 05, 2014	Jul. 29, 2013	Jan. 28, 2013
Stockholders Equity [Line Items]
Common stock repurchased					$ 20,000,000	$ 11,541,000	$ 18,809,000
Number of cumulative shares repurchased				405,290
Stock repurchased average price per share				$ 25.47		$ 23.77
Common stock repurchased, Shares						485,777	795,643
Subsequent Event [Member]
Stockholders Equity [Line Items]
Stock repurchase program authorized amount								$ 20,000,000
Remaining amount available for repurchases of shares								$ 30,000,000
January 2013 authorization plan [Member]
Stockholders Equity [Line Items]
Stock repurchase program authorized amount											$ 10,000,000
Previous authorization plan [Member]
Stockholders Equity [Line Items]
Common stock repurchased				$ 300,000
July 2013 authorization plan [Member]
Stockholders Equity [Line Items]
Stock repurchase program authorized amount										$ 20,000,000
Stock repurchased average price per share			$ 21.71
Amount available for repurchases of shares			$ 11,500,000				$ 11,500,000
Common stock repurchased, Shares			390,353
Open Market Share Repurchase Program [Member]
Stockholders Equity [Line Items]
Common stock repurchased							$ 1,000,000
Accelerated Share Repurchase Program [Member]
Stockholders Equity [Line Items]
Stock repurchase program authorized amount									$ 30,000,000
Common stock repurchased, Shares	89,721	758,143
Remaining amount available for repurchases of shares									$ 10,000,000
Accelerated Share Repurchase Program [Member] | Investment Bank [Member]
Stockholders Equity [Line Items]
Stock repurchased average price per share		$ 23.59
Common stock repurchased, Shares		847,864
Payments for repurchase of common stock		$ 20,000,000
Fair value of common stock		16,000,000
Reduction in common stock		100,000
Reduction in additional paid-in capital		(2,500,000)
Reduction in retained earnings		13,500,000
Initial payment to bank reported as reduction in retained earnings		$ 4,000,000