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Stock-Based Compensation - Summary of Option Activity under Stock-Based Compensation Plan (Detail) - $ / shares | 12 Months Ended |
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Sep. 30, 2017 | Sep. 30, 2016 | Sep. 30, 2015 | Sep. 30, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Number of Shares, Options granted | 365,000 |  |  |
2009 Plan [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Number of Shares, Options granted | 0 | 75,000 |  |
Number of Shares, Options exercised | (43,750) | (37,875) | (28,125) |
Number of Shares, Options outstanding | 440,000 | 483,750 | 446,625 | 474,750
Average Exercise Price Per Share, Options granted |  | $ 8.760 |  |
Average Exercise Price Per Share, Options exercised | $ 5.126 | 5.126 | $ 4.839 |
Average Exercise Price Per Share, Options outstanding | $ 5.739 | $ 5.684 | $ 5.120 | $ 5.103
1997 Plan [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Number of Shares, Options exercised |  | (30,000) |  |
Number of Shares, Options expired |  | (11,250) |  |
Number of Shares, Options outstanding | 0 |  | 41,250 | 41,250
Average Exercise Price Per Share, Options exercised |  | $ 6.213 |  |
Average Exercise Price Per Share, Options expired |  | $ 6.213 |  |
Average Exercise Price Per Share, Options outstanding |  |  | $ 6.213 | $ 6.213

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- Definition Number of options or other stock instruments for which the right to exercise has lapsed under the terms of the plan agreements. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(1)(iv)(4) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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- Definition Number of options outstanding, including both vested and non-vested options. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(1)(i)-(ii) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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