Right of holders to elect company's board of directors.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Date the equity-based award expires, in CCYY-MM-DD format.

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Number of shares authorized for issuance under share-based payment arrangement.

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The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

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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.

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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 remaining contractual term for option awards outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Shareholders' Equity and Stock-Based Compensation - Additional Information (Detail) - shares	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018	Mar. 17, 2009
Class of Stock [Line Items]
Common stock options issued to employees	177,492
Number of shares, options outstanding	252,492	272,492	317,492
2009 Plan [Member]
Class of Stock [Line Items]
Common stock options issued to employees	0
Shares available for granting	0
Remaining contractual life on the options outstanding	1 year 7 months 6 days
Number of options, forfeited or cancelled	0
Common Stock [Member]
Class of Stock [Line Items]
Right of holders to elect company's board of directors	25.00%
Common Stock [Member] \| 2009 Plan [Member]
Class of Stock [Line Items]
Maximum number of shares granting of awards				800,000
Class B Stock [Member]
Class of Stock [Line Items]
Right of holders to elect company's board of directors	75.00%	75.00%
Class B Stock [Member] \| 2009 Plan [Member]
Class of Stock [Line Items]
Maximum number of shares granting of awards				160,000
Class B Stock [Member] \| 2009 Plan [Member] \| Share-based Compensation Award, Tranche One [Member]
Class of Stock [Line Items]
Number of shares, options outstanding	45,000	45,000
Share based payments, options, expiration date	Oct. 01, 2021	Oct. 01, 2021
Class B Stock [Member] \| 2009 Plan [Member] \| Share-based Compensation Award, Tranche Two [Member]
Class of Stock [Line Items]
Number of shares, options outstanding	30,000	30,000
Share based payments, options, expiration date	Sep. 26, 2026	Sep. 26, 2026