Stock-Based Compensation Plans - Schedule of Stock Option Activity (Detail) - $ / shares	12 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2014
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Number of Shares Outstanding, Beginning balance	1,118,008	1,210,619	1,368,984
Number of Shares, Granted	241,582	164,401	138,837
Number of Shares, Exercised	(437,850)	(166,422)	(190,434)
Number of Shares, Forfeited and expired	(94,415)	(90,590)	(106,768)
Number of Shares Outstanding, Ending balance	827,325	1,118,008	1,210,619
Number of Shares, Exercisable	434,876
Weighted Average Exercise Price, Beginning Balance	$ 20.10	$ 20.35	$ 20.13
Weighted Average Exercise Price, Granted	20.63	21.24	22.71
Weighted Average Exercise Price, Exercised	15.68	14.54	14.42
Weighted Average Exercise Price, Forfeited and expired	31.52	35.35	31.26
Weighted Average Exercise Price, Ending balance	21.30	$ 20.10	$ 20.35
Weighted Average Exercise Price, Exercisable	$ 21.50