Net Income Per Share Data - Additional Information (Detail) (USD $)	0 Months Ended	3 Months Ended		6 Months Ended
	Nov. 11, 2014	Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2015	Mar. 31, 2014	Nov. 05, 2014
Earnings Loss Per Share [Line Items]
Weighted average diluted shares outstanding excluded outstanding stock options		300,000	200,000	500,000	400,000
Common stock repurchased, Shares				758,143	485,577
Common stock repurchased				$ 16,000,000	$ 11,500,000
Amount available for repurchases of shares		14,000,000		14,000,000
Common stock closing stock price	$ 21.38
Volume weighted average price per share	$ 1.00
Volume weighted average price description				For every $1.00 increase or decrease in the Company's VWAP, based on a closing stock price of $21.38 on November 11, 2014, the settlement amount will change by approximately 45,000 shares.
Stock issued for settlement	45,000
Accelerated Share Repurchase Program [Member]
Earnings Loss Per Share [Line Items]
Maximum payments for repurchase of common stock						30,000,000
Fair value of common stock	16,000,000
Shares repurchased	758,143
Initial payment to bank reported as reduction in retained earnings	4,000,000
Maximum number of shares of common stock issued	1,870,907
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
Accelerated Share Repurchase Program [Member] | Wells Fargo [Member]
Earnings Loss Per Share [Line Items]
Amount available for repurchases of shares		$ 4,000,000		$ 4,000,000