Stock-based Compensation Plans - Schedule of Stock Option Activity (Detail) - $ / shares	12 Months Ended
Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Number of Options Outstanding, Beginning balance	871,000	711,000	1,002,000
Number of Options, Granted	299,000	179,000	270,000
Number of Options, Exercised	(125,000)	(13,000)	(450,000)
Number of Options, Forfeited and expired	(105,000)	(6,000)	(111,000)
Number of Options Outstanding, Ending balance	940,000	871,000	711,000
Number of Options, vested and exercisable	472,000
Weighted Average Exercise Price, Beginning Balance	$ 32.18	$ 26.28	$ 21.54
Weighted Average Exercise Price, Granted	41.06	55.09	34.08
Weighted Average Exercise Price, Exercised	22.89	22.03	19.46
Weighted Average Exercise Price, Forfeited and expired	41.69	42.28	30.18
Weighted Average Exercise Price, Ending balance	35.18	$ 32.18	$ 26.28
Weighted Average Exercise Price, vested and exercisable	$ 28.65

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The number of shares into which fully or partially vested stock options outstanding as of the balance sheet date can be currently converted under the option plan.

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The weighted-average price as of the balance sheet date at which grantees can acquire the shares reserved for issuance on vested portions of options outstanding and currently exercisable under the stock option plan.

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For presentations that combine terminations, the number of shares under options that were cancelled during the reporting period as a result of occurrence of a terminating event specified in contractual agreements pertaining to the stock option plan or that expired.

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Weighted average price of options that were either forfeited or expired.

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Gross number of share options (or share units) granted during the period.

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Number of options outstanding, including both vested and non-vested options.

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Weighted average price at which grantees can acquire the shares reserved for issuance under the stock option plan.

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Weighted average price at which option holders acquired shares when converting their stock options into shares.

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Weighted average per share amount at which grantees can acquire shares of common stock by exercise of options.

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Number of share options (or share units) exercised during the current period.

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