Stock-Based Compensation Plans - Schedule of Stock Option Activity (Detail) - $ / shares	12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2013
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Number of Shares Outstanding, Beginning balance	1,210,619	1,368,984	1,325,438
Number of Shares, Granted	164,401	138,837	178,924
Number of Shares, Exercised	(166,422)	(190,434)	(10,273)
Number of Shares, Forfeited	(90,590)	(106,768)	(125,105)
Number of Shares Outstanding, Ending balance	1,118,008	1,210,619	1,368,984
Number of Shares, Exercisable	797,045
Weighted Average Exercise Price, Beginning Balance	$ 20.35	$ 20.13	$ 21.25
Weighted Average Exercise Price, Granted	21.24	22.71	20.85
Weighted Average Exercise Price, Exercised	14.54	14.42	14.40
Weighted Average Exercise Price, Forfeited	35.35	31.26	33.47
Weighted Average Exercise Price, Ending balance	20.10	$ 20.35	$ 20.13
Weighted Average Exercise Price, Exercisable	$ 20.04