Stockholders' Equity - Additional Information (Detail) - USD ($)			12 Months Ended
	Jul. 08, 2015	Nov. 11, 2014	Sep. 30, 2017	Sep. 30, 2015	Nov. 06, 2015	Nov. 05, 2014
Stockholders Equity [Line Items]
Common stock repurchased, Shares			196,190
Payments for repurchase of common stock			$ 4,702,000	$ 20,000,000
Stock repurchased average price per share			$ 23.97
Remaining amount available for repurchases of shares			$ 25,300,000
Accelerated Share Repurchase Program [Member]
Stockholders Equity [Line Items]
Maximum payments for repurchase of common stock					$ 20,000,000	$ 30,000,000
Common stock repurchased, Shares		847,864
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
Accelerate share repurchase program, price per share		$ 23.59
Accelerated Share Repurchase Program [Member] | Investment Bank [Member]
Stockholders Equity [Line Items]
Common stock repurchased, Shares		758,143
Fair value of common stock		$ 20,000,000
Transaction One [Member] | Accelerated Share Repurchase Program [Member]
Stockholders Equity [Line Items]
Common stock repurchased, Shares		758,143
Transaction Two [Member] | Accelerated Share Repurchase Program [Member]
Stockholders Equity [Line Items]
Common stock repurchased, Shares	89,721