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Stock-Based Compensation - Summary of Option Activity under Stock-Based Compensation Plan (Detail) - 2009 Plan [Member] - $ / shares	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Shares, Options exercised	(122,508)	(43,750)
Number of Shares, Options outstanding	317,492	440,000	483,750
Average Exercise Price Per Share, Options exercised	$ 5.104	$ 5.126
Average Exercise Price Per Share, Options outstanding	$ 5.984	$ 5.739	$ 5.684

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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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